Vacuum leak? Marc has me confused now!

[KILLSHOTS]

Hey guys,

My vacuum pump (under the pass. headlight) cycles on for a moment every 4 to 5 seconds, when the ignition is on with the car not running. I've come to understand that this indicates a vacuum leak somewhere under the plenum. A no-brainer, right?

BUT, on page 19 of the latest HOTB, Marc says in his troubleshooting tips:

"If the pump cycles on and off the vacuum connections up to the secondary port solenoid are tight. As long as the pump will turn off for one second, the secondary port throttles will operate normally. If the pump shuts off for longer than five seconds it indicates that the vacuum system connections are tighter than average."

So, according to Marc, my vacuum system connections are tight? Am I misunderstanding what I've just read? Anybody willing to help confuse me further?

Thanks!
Chris

[KILLSHOTS]

Also, forgot to mention that my car idles normally...no high idle.

[Racinfan83]

Mine cycles like yours. Runs for 2-3 seconds, off for 4-5 seconds. I took my car to Marc last fall for injectors, coils, radiator clean, and tuning - he said mine was perfectly normal. He drove it with his laptop hooked up to it as well - and all was good....

[JohnG]

Mine does the same. I also thought I had a leak. Glad to know otherwise.

[KILLSHOTS]

WOW, I'm kinda shocked...lots of views but not many replies. Anybody have any thoughts on this?

[KILLSHOTS]

Mine cycles like yours. Runs for 2-3 seconds, off for 4-5 seconds. I took my car to Marc last fall for injectors, coils, radiator clean, and tuning - he said mine was perfectly normal. He drove it with his laptop hooked up to it as well - and all was good....
Thanks Racinfan, good to know Marc gave yours his seal of approval!

[Blue Flame Restorations]

A good working secondary system is a good setup. My 95 works fine...for now. My 91 has no secondary hardware and will never have a leak from that area.

[KILLSHOTS]

A good working secondary system is a good setup. My 95 works fine...for now. My 91 has no secondary hardware and will never have a leak from that area.
Thanks for getting back, Brett! But my question for you and the rest of our brothers is this:

The conventional wisdom (or my rookie understanding of it) is that a cycling pump means an under-the-plenum vacuum leak. Is that correct? Does my cycling pump mean that I have a vacuum leak? Or do I understand what I read from Marc correctly? If so, John and Racinfan and I don't have leaks. What are your thoughts?

Everybody?

[Blue Flame Restorations]

Honestly, I'm not the person with that specific knowledge. I trust in Marc and Pete. I truly wish I was the expert to give you the answer.

Sincerely
Brett

[KILLSHOTS]

Thanks Brett. I'm with you on trusting Marc. I woke up today thinking I had a leak. Now I don't and I didn't have to pull the plenum...I'd call that a good day! LOL

Great night all!
Chris

[PhillipsLT5]

Can you @ 3k feel the secondaries opening? A burst of power?
I think you are OK, but in the future just remove this stuff, no confusion just + 10 RWHP with tune

[XfireZ51]

The point of the secondary pump is to make certain there's enough vacuum to open the secondaries. It is not the main source of vacuum, the motor is. So w motor OFF, the pump becomes the primary source. It's normal for it to cycle. As Marc has said, all motors have some level of vacuum leak but most not enough to make a difference.

[KILLSHOTS]

The point of the secondary pump is to make certain there's enough vacuum to open the secondaries. It is not the main source of vacuum, the motor is. So w motor OFF, the pump becomes the primary source. It's normal for it to cycle. As Marc has said, all motors have some level of vacuum leak but most not enough to make a difference.
Thanks XFire, makes sense to me.

[KILLSHOTS]

Can you @ 3k feel the secondaries opening? A burst of power?
I think you are OK, but in the future just remove this stuff, no confusion just + 10 RWHP with tune
Hey Phillip!

Oh yeah, it's VERY strong. The fury on mine starts at more like 4000, due to the stock gearing, but I certainly never thought I was giving up any horsepower to a vacuum leak, that's for sure! And I agree, at some point I'll just remove it.

[Hog]

Hey Phillip!

Oh yeah, it's VERY strong. The fury on mine starts at more like 4000, due to the stock gearing, but I certainly never thought I was giving up any horsepower to a vacuum leak, that's for sure! And I agree, at some point I'll just remove it.

The gearing of your rearend wont affect the rpm at which your engine begins to pull. Only engine mods will affect that.

[KILLSHOTS]

The gearing of your rearend wont affect the rpm at which your engine begins to pull. Only engine mods will affect that.
Hey Hog,

I was referring mainly to the PERCEPTION of when the big power comes on. As Marc says, with a 4:10 upgrade, "the really useful area begins at 3000 instead of 4000 RPM."

Chris

[Hib Halverson]

The point of the secondary pump is to make certain there's enough vacuum to open the secondaries. It is not the main source of vacuum, the motor is. (snip)

Not.

The engine is the source of vacuum which opens the SPTs but once MAP continues to rise, as it undoubtedly will do as the the engine enters high-part throttle and reaches wide open throttle, the pressure in the intake tract is too high (or the vacuum is too low) to keep the SPTs open.

Remember, WOT means low/no vacuum but the SPT actuators need vacuum to work.

[Hib Halverson]

Reading this thread again, got me thinking...

As a rule, I agree with Marc Haibeck on most significant issues relating to LT5 performance/drivability, but on the Secondary Port Throttle vacuum system, if Marc feels that as long as the auxiliary vacuum pump will shut off for a second or so, the port throttles will work properly, I disagree.

Key parts of the port throttle system are the vacuum motors which open and close the SPTs, a small vacuum reservoir, the auxiliary vacuum pump, various controlling/sensing devices and the plumbing. The system is controlled by the ECM and can be disabled with the "power switch" or "valet switch".

Once the power key is on and the ECM decides the port throttles should open, engine manifold absolute pressure, which is below atmospheric at the time the port throttles are to be opened, is fed to the port throttle actuators and the SPTs open. Manifold vacuum also is also fed to a small "vacuum" reservoir down under the intake plenum.

As the main throttle continues to open and load on the engine increases, manifold pressure increases to nearly atmospheric. Of course, that's not enough to continue to overcome the return springs in the SPT actuators, so...what holds the SPTs open? For a short period, the lower pressure level in the vacuum reservoir.

Ok...riddle me this: what happens during a period of high part throttle or wide open throttle operation long enough for the pressure in the vacuum reservoir to begin to rise towards MAP. What keeps the SPTs open, then?

Well, that's why GM added an auxiliary vacuum pump to the system. Once pressure in the SPT system goes rises above 61-kPa (or, drops below 41-kPa vacuum), the pump kicks on to keep the pressure in the SPT system low enough to overcome the SPT actuators' spring pressure and hold the port throttles open.

Now, what happens when the system leakage is enough that aux. vac. pump cannot maintain a low enough pressure to hold the port throttles open? If the SPTS are commanded open and MAP rises above 80.3-kPa (or, drops below 21-kPa vacuum) for more than two seconds, the ECM sets DTC61, turns the MIL on and sets the rev limit to 3000 RPM.

So when can a leaking SPT system set DTC61, try climbing a long hill at 80 mph and at higher altitude–say 4000 feet or above. Or try a long acceleration in fifth gear.

The bigger the leak in the system, the sooner that code will set and the pump running once every second seems like a pretty big leak or a weak pump to me.

Bottom line, if your secondary port throttle system leaks or the vacuum pump is too weak to hold a pressure low enough to turn off, for not just one second, but 15 seconds or so, repair the system. The instructions on troubleshooting and repairing the SPTs are in the Service Manual.

SPT fun fact: Peel off the label from the vacuum reservoir under the plenum and you'll find a Ford part number.

[scottfab]

Reading this thread again, got me thinking...

As a rule, I agree with Marc Haibeck on most significant issues relating to LT5 performance/drivability, but on the Secondary Port Throttle vacuum system, if Marc feels that as long as the auxiliary vacuum pump will shut off for a second or so, the port throttles will work properly, I disagree.

....snip...


Bingo. You can now give yourself the "beacon of reality" award ;)

I have voice this opposing view in the past also. Along with what Hib mentions about ability to hold the secondaries in, to me a 1sec cycle time is both an indication of a worsening issue AND ages the crap out of the pump (key on motor off)

Hib, conventional thinking in the 90s was that 10sec was the limit as to "better fix it" but 15 is good also. I keep mine at 30sec. When it goes below that I investigate. That way I don't find myself piss-whine and moaning about secondary failures. [-X

PS it is less fashionable nowadays to "disagree" on the forum but
I think done correctly it's just fine.

[XfireZ51]

Here's a page from the FSM. The secondary pump is considered a "crutch" to any lack of vacuum. Don't forget, there's a reservoir and a solenoid involved. However, the secondary pump is not the primary source of vacuum at WOT.

No offense Hib, I appreciate your writing but I'll go with the guy that has worked on LT-5s for over 15 years. This issue came up just a week ago regarding a 95.
Marc was there to describe the operation of the secondaries. Of course, my ZR is bastardized since it doesn't have secondaries any more.


http://i187.photobucket.com/albums/x198/Z51Xfire/c6300dbb506dbe07969d02c139dc2120_zpse4c2b39b.jpg

[mike100]

The secondary vacuum pump runs to first charge the mini reservoir which you hear with ign on. This is just a reserve to prevent a delayed response of the secondary diaphragms.

The vacuum pump will also turn on when you step on it and open the throttle blades enough for the manifold vacuum to drop or whenever the ecm sees appropriate engine load and minimum rpm etc to open secondary ports. The vacuum pump runs at about 13" of vacuum as long as it needs to sustain the secondary high power mode. Once you back off of it, the manifold vacuum rises anyways. The pump turns off once the mini reservoir is again 'charged'.

I observed this when I hooked up a vacuum gauge to my secondary diagnostic map sensor and watched it as I drove around.

[mike100]

It is kind of dumbed-down and runs even though there is enough vacuum to hold the diaphragms open indefinitely. I guess they assumed a leaky system and provided enough pump oomph to make it work with a minor vacuum seal issue. They also could have used another 1-way check valve, but just decided to keep the pump on until vacuum was no longer needed. it just keeps running when you are at full throttle. I saw the vac gauge needed pulsing the entire duration of full power with the pump so I know this is the case.

[KILLSHOTS]

It is kind of dumbed-down and runs even though there is enough vacuum to hold the diaphragms open indefinitely. I guess they assumed a leaky system and provided enough pump oomph to make it work with a minor vacuum seal issue. They also could have used another 1-way check valve, but just decided to keep the pump on until vacuum was no longer needed. it just keeps running when you are at full throttle. I saw the vac gauge needed pulsing the entire duration of full power with the pump so I know this is the case.
So you're saying the secondary pump always runs at full throttle, even when you don't have any vacuum leaks? Interesting.

[XfireZ51]

Mike,

The point is the pump is a supplement not the primary. Why bother w the rest if the pump was able to support the secondaries on its own?
HERE's a question for Hib. On the 24 hour run, was there a secondary pump in use?

[mike100]

So you're saying the secondary pump always runs at full throttle, even when you don't have any vacuum leaks? Interesting.

I thought about that...Maybe mine leaks?, but I doubt it because it was all good a couple of years ago when I tested each line chasing vacuum leaks. My test runs were only for a few seconds because I was just tooling around town in 2nd and 3rd gear.

Also note that the secondaries stay open until you let off the pedal all the way so during those light cruise conditions, the manifold vacuum keeps 'em open via the 1-way check valve that is in circuit.

[KILLSHOTS]

Mike,

The point is the pump is a supplement not the primary. Why bother w the rest if the pump was able to support the secondaries on its own?
HERE's a question for Hib. On the 24 hour run, was there a secondary pump in use?
Could that pump have handled running nearly non-stop for 24 hours?

[XfireZ51]

Could that pump have handled running nearly non-stop for 24 hours?

Well if it's the primary source for the secondaries, it would need to be, no?

[KILLSHOTS]

I thought about that...Maybe mine leaks?, but I doubt it because it was all good a couple of years ago when I tested each line chasing vacuum leaks. My test runs were only for a few seconds because I was just tooling around town in 2nd and 3rd gear.

Also note that the secondaries stay open until you let off the pedal all the way so during those light cruise conditions, the manifold vacuum keeps 'em open via the 1-way check valve that is in circuit.
Maybe yours leaks a little, which is what I think mine is doing, but it doesn't seem like it must be a big deal, especially since we aren't idling high. I definitely value Hib's input and frankly, what he's saying make a lot of sense, even to my non-engineer mind. But if I parse his expert advice with Marc's expert advice, it seems like I have an issue but not one that I should be pulling the plenum tomorrow to correct.

[XfireZ51]

I thought about that...Maybe mine leaks?, but I doubt it because it was all good a couple of years ago when I tested each line chasing vacuum leaks. My test runs were only for a few seconds because I was just tooling around town in 2nd and 3rd gear.

Also note that the secondaries stay open until you let off the pedal all the way so during those light cruise conditions, the manifold vacuum keeps 'em open via the 1-way check valve that is in circuit.

Marc said EVERY LT-5 leaks to one extent or another. That's why there's a pump.

[KILLSHOTS]

Marc said EVERY LT-5 leaks to one extent or another. That's why there's a pump.
Aha, grasshoppa!

Pump not there to reveal problem, pump there to help fix problem!

[XfireZ51]

Pump is there to make up for problem.

[Paul Workman]

Reading this thread again, got me thinking...

As a rule, I agree with Marc Haibeck on most significant issues relating to LT5 performance/drivability, but on the Secondary Port Throttle vacuum system, if Marc feels that as long as the auxiliary vacuum pump will shut off for a second or so, the port throttles will work properly, I disagree.

Key parts of the port throttle system are the vacuum motors which open and close the SPTs, a small vacuum reservoir, the auxiliary vacuum pump, various controlling/sensing devices and the plumbing. The system is controlled by the ECM and can be disabled with the "power switch" or "valet switch".

Once the power key is on and the ECM decides the port throttles should open, engine manifold absolute pressure, which is below atmospheric at the time the port throttles are to be opened, is fed to the port throttle actuators and the SPTs open. Manifold vacuum also is also fed to a small "vacuum" reservoir down under the intake plenum.

As the main throttle continues to open and load on the engine increases, manifold pressure increases to nearly atmospheric. Of course, that's not enough to continue to overcome the return springs in the SPT actuators, so...what holds the SPTs open? For a short period, the lower pressure level in the vacuum reservoir.

Ok...riddle me this: what happens during a period of high part throttle or wide open throttle operation long enough for the pressure in the vacuum reservoir to begin to rise towards MAP. What keeps the SPTs open, then?

Well, that's why GM added an auxiliary vacuum pump to the system. Once pressure in the SPT system goes rises above 61-kPa (or, drops below 41-kPa vacuum), the pump kicks on to keep the pressure in the SPT system low enough to overcome the SPT actuators' spring pressure and hold the port throttles open.

Now, what happens when the system leakage is enough that aux. vac. pump cannot maintain a low enough pressure to hold the port throttles open? If the SPTS are commanded open and MAP rises above 80.3-kPa (or, drops below 21-kPa vacuum) for more than two seconds, the ECM sets DTC61, turns the MIL on and sets the rev limit to 3000 RPM.

So when can a leaking SPT system set DTC61, try climbing a long hill at 80 mph and at higher altitude–say 4000 feet or above. Or try a long acceleration in fifth gear.

The bigger the leak in the system, the sooner that code will set and the pump running once every second seems like a pretty big leak or a weak pump to me.

Bottom line, if your secondary port throttle system leaks or the vacuum pump is too weak to hold a pressure low enough to turn off, for not just one second, but 15 seconds or so, repair the system. The instructions on troubleshooting and repairing the SPTs are in the Service Manual.

SPT fun fact: Peel off the label from the vacuum reservoir under the plenum and you'll find a Ford part number.

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/plenumvacuumcircuitsLT5LargeLarge.jpg (http://s185.photobucket.com/user/6PPC_bucket/media/tech%20files/plenumvacuumcircuitsLT5LargeLarge.jpg.html)

Marc should correct me if I'm wrong, but I don't believe he's saying a short "OFF" cycle doesn't need attention, but rather if the leak is small enough that the vacuum pump can attain sufficient vacuum to reach pump cut-off threshold, then the the SPTs actuators will not be inhibited for lack of vacuum (provided code 61 is not triggered). (Referring to the diagram above)

The SPT circuit is divided into two parts, partitioned by the SECONDARY PORT THROTTLE VALVE (switch):


The pump and the engine vacuum charge the reservoir side of the (VALVE) and
the other half of the circuit connects the (valve) to the vacuum actuators.


So, IF the vacuum pump will cycle OFF - for even a second, then sufficient vacuum exists to operate the SPT actuators, at least up to the SPT VALVE (valve). Now, however, if the circuit on the actuator side of the (valve) is severely compromised to the point of triggering code 61 when the ECM calls for the secondaries to open, we know the actuator side of the circuit is what is severely compromised.

Back to Scottfab's point about the short "OFF" cycling and pump longevity:

If a pump is short (off) cycling, I wouldn't argue there isn't an issue to be attended to. However, most of the time the engine provides the vacuum sufficient to charge and maintain the reservoir side of the (valve). The pump doesn't run at all until there is a sustained load to raise air pressure above the point the pump is triggered "ON". This significantly mitigates the concern for pump being over-worked (but I'd want to run that down at the earliest convenience). But, then again, during the 24 hour run, I would think the pump ran (ed. as needed) majority of the time, especially at/near WOT!

Of course one could perform the secondary delete mod and NEVER worry about this entire topic again...But, that is another debate.

[Hib Halverson]

Here's a page from the FSM. 'Preciate the time to shoot a pic and post it but, you didn't need to do that. I have FSMs from 1982-2012 and have read that page a number of times.No offense Hib, I appreciate your writing but I'll go with the guy that has worked on LT-5s for over 15 years.Even Marc's 15 years of experience, which I greatly respect (heck, I've had him work on my '04 and I use his cals in my '95) cannot negate the fact that when an engine like the LT5 is at WOT, there is virtually no vacuum present. If you don't believe me, connect your scan tester and go for a road test. Pick third or fourth gear then accelerate at 100% TPS and watch the MAP reading. It will be very close to atmospheric, ie: virtually no vacuum.

With 90-92, almost all time at WOT, the SPTs are commanded open and with 93-95 it's all the time. Thus, for most of the time the SPTs are open, while vacuum may be present to open them, there's little or no vacuum to keep them open, so the primary source of vacuum is not MAP but is, first, the vacuum tank, followed afterwards, by the pump.(snip)
HERE's a question for Hib. On the 24 hour run, was there a secondary pump in use?I never saw the Record Run engine with the plenum off so I can't verify the existence of port throttles on it. Could that pump have handled running nearly non-stop for 24 hours?Might be a moot question because for the entire run (5000-km, 24-hr and 5000-mi), the engine was never run at WOT. It had a throttle stop, so there was always some level of vacuum present. At high rpm, it may have been quite a bit of vacuum because of the restriction part throttle must have been in the intake tract. It wasn't until after they set the 5000-mi. mark that the final driver, Stu Hayner, was told to remove the throttle stop and take a few laps at WOT.

There was a so-called "touch the sky" test done during the final stages of ZR-1 development. I think it was done at the now-defunct Desert Proving Ground where a ZR-1 was run on the high-banked track at WOT for the duration of a tank of fuel so the aux. vac. pump will last at least that long in continuous use.Marc said EVERY LT-5 leaks to one extent or another. That's why there's a pump.

That is NOT why there is a pump.

HIB, your post was moderated for "some" of its content. PM sent.

[scottfab]

Marc should correct me if I'm wrong, but I don't believe he's saying a short "OFF" cycle doesn't need attention, but rather if the leak is small enough that the vacuum pump can attain sufficient vacuum to reach pump cut-off threshold, then the the SPTs actuators will not be inhibited for lack of vacuum (provided code 61 is not triggered). (Referring to the diagram above)

My sense for it is that you are mostly correct. However, running that close to failure is not the best solution. In fact the system is on the verge of failure (code being set) and will dip in and out of failure. This is not by any means or stretch of the imagination a good approach. Why not just fix it and be done with it. To propagate the notion that 1sec between cycles is "OK" is like saying you can run your tires at 25psi and that it's ok to ignore filling the tires until the "Low Tire Pressure" light comes on. I do not recommend either.

Getting above 15sec and in fact achieving 30sec or more cycle time on the pump is not hard. Attention do detail is the key. Really going after and fixing leaks and contamination is key (if you live in a heavy dust filled and/or dirt filled environment then all bets are off)

So, IF the vacuum pump will cycle OFF - for even a second, then sufficient vacuum exists to operate the SPT actuators, at least up to the SPT VALVE (valve). Now, however, if the circuit on the actuator side of the (valve) is severely compromised to the point of triggering code 61 when the ECM calls for the secondaries to open, we know the actuator side of the circuit is what is severely compromised.

Yes, one can wait until there is total failure just as one can keep driving when the "RESERVE" notice is given on the dash. I prefer not to and would never suggest that members think it is OK to keep driving when the "RESERVE" light is lit. Similarly, a 1sec pump interval is a BIG TIME warning. AND I submit is not proven to NOT set a code at 1sec pump interval time. In fact I know positively that you'll get a roll off of power at about 4k and NOT see a code 61.
(marginal condition)

Back to Scottfab's point about the short "OFF" cycling and pump longevity:

If a pump is short (off) cycling, I wouldn't argue there isn't an issue to be attended to. However, most of the time the engine provides the vacuum sufficient to charge and maintain the reservoir side of the (valve). The pump doesn't run at all until there is a sustained load to raise air pressure above the point the pump is triggered "ON".

Agreed, most of the time if the engine is running. However, I stated
"key on engine off". Not a great concern because it is usually rare for key on engine off but it does happen. This is not a fish pump we're talking about. It is not intended to run 100% duty cycle 24/7.
If a pump is cycling every 1sec with key on engine off, just fix it.
Gezzz

This significantly mitigates the concern for pump being over-worked (but I'd want to run that down at the earliest convenience). But, then again, during the 24 hour run, I would think the pump ran majority of the time, especially at/near WOT!

Interesting, I wonder about "most of the time". My guess would be there is enough vacuum at 174mph to run the actuators with out the pump "most of the time" :)
On each curve and WOT maybe it's on. Straightaways? dunno

Of course one could perform the secondary delete mod and NEVER worry about this entire topic again...But, that is another debate.

yes that would "fix" it. But then would it be an LT5? One wonders.
I suppose it is. I mean the block is still there.

Back in 99 I came up with a solenoid actuator replacement that pulled a cable. I was convince it would be a permanent solution. However about that time I ended up
actually fixing the secondary system and it has stayed fix all of these years, save the time the rebuilt pump failed (poor selection of replacement diaphragm material) . At that time (99) I announced I would, upon another secondary system failure, put that solenoid in and make public the part numbers etc. So far it hasn't come to that.
I do still have all the parts etc in a box. I think ripping out the secondary is out of the question for me for several reasons.
eh, but then that's just me. I still keep the spare tire and the owner's manual too :)
Respectfully submitted:

[Hib Halverson]

(snip)

Interesting, I wonder about "most of the time". My guess would be there is enough vacuum at 174mph to run the actuators with out the pump "most of the time" :)
On each curve and WOT maybe it's on. Straightaways? dunno(snip)

Guys...the Record Run engine was throttle stopped so there was always vacuum present in the plenum. If that engine had port throttles, which I suspect it did because the it came right off the LT5 Line at Stillwater, it's likely the pump didn't run that much.

[scottfab]

Guys...the Record Run engine was throttle stopped so there was always vacuum present in the plenum. If that engine had port throttles, which I suspect it did because the it came right off the LT5 Line at Stillwater, it's likely the pump didn't run that much.

Didn't see your previous post to mine.
Do you know or suspect what the thinking was to put the stop in?

[Dynomite]

BUT, on page 19 of the latest HOTB, Marc says in his troubleshooting tips:

"If the pump cycles on and off the vacuum connections up to the secondary port solenoid are tight. As long as the pump will turn off for one second, the secondary port throttles will operate normally. If the pump shuts off for longer than five seconds it indicates that the vacuum system connections are tighter than average."

So, according to Marc, my vacuum system connections are tight? Am I misunderstanding what I've just read? Anybody willing to help confuse me further?

Thanks!
Chris

I Concur with Marc :cheers:
If the vacuum pump cycles 5, 10, 15 seconds or at all....the vacuum system is NOT TIGHT but normal and functional for the age of the vacuum system with components not replaced with NEW LINES AND NEW RUBBER (soft) CONNECTORS.

Disconnect the drivers side center plenum vacuum source and hold your finger over the rubber connector disconnected (Engine OFF but Key ON). IF THE SECONDARIES (Secondary Canisters) FUNCTION AND HOLD POSITION WHEN TESTING SECONDARIES WITH PLENUM IN PLACE (Key on) Verifying Secondary Actuator Operation with the Plenum in Place (http://www.zr1specialist.com/HAT%20Web/articles/Verifying%20Secondary%20Actuator%20Operation.pdf) END OF DISCUSSION ;)

I will think further on this but for now I am busy planting corn and beans ;)

[KILLSHOTS]

I Concur with Marc :cheers:
If the vacuum pump cycles 5, 10, 15 seconds or at all....the vacuum system is NOT TIGHT but normal and functional for the age of the vacuum system with components not replaced with NEW LINES AND NEW RUBBER (soft) CONNECTORS.

Disconnect the drivers side center plenum vacuum source and hold your finger over the rubber connector disconnected (Engine OFF but Key ON). IF THE SECONDARIES (Secondary Canisters) FUNCTION AND HOLD POSITION WHEN TESTING SECONDARIES WITH PLENUM IN PLACE (Key on) Verifying Secondary Actuator Operation with the Plenum in Place (http://www.zr1specialist.com/HAT%20Web/articles/Verifying%20Secondary%20Actuator%20Operation.pdf) END OF DISCUSSION ;)

I will think further on this but for now I am busy planting corn and beans ;)
I'll try this. Thanks!!

[scottfab]

Maybe yours leaks a little, which is what I think mine is doing, but it doesn't seem like it must be a big deal, especially since we aren't idling high. I definitely value Hib's input and frankly, what he's saying make a lot of sense, even to my non-engineer mind. But if I parse his expert advice with Marc's expert advice, it seems like I have an issue but not one that I should be pulling the plenum tomorrow to correct.

With key on and engine off how long does the pump run and how long does it stay off (approximately) ?

[KILLSHOTS]

With key on and engine off how long does the pump run and how long does it stay off (approximately) ?
It runs for only an instant...less than a second. Then, it stays off for 4 to 5 seconds. Then repeat.

[Hib Halverson]

Didn't see your previous post to mine.
Do you know or suspect what the thinking was to put the stop in?

The engine had more power than GM thought was necessary to set the record.

To ensure durability, best fuel economy at the target speed and ensure no consistent throttle opening, the engine had a throttle stop.

The durability issue was the biggest reason. In 1990, no one had ever run any production car in an attempt to set the 24-hr speed record. The previous attempts (Ford, Mercedes, Audi) were done with modified or purpose-built vehicles. No one knew if the LT5 would last. In fact, GM was so worried the attempt would fail, the Record Run was done in secrecy with few media present and only limited documentation by internal GM and sponsors.

[scottfab]

It runs for only an instant...less than a second. Then, it stays off for 4 to 5 seconds. Then repeat.

It's probably the check valve (most common) but you'd want to
find the little black hose and trace it up toward the engine.
You'll find a rubber connector about half way up. Open it.
Put you finger over the hose that runs tot he pump.
The pump should run and then stop. Keep it plugged.
The pump should not run again (wait over 60sec).
If all ok then the leak is under the plenum (check valve etc).
If the pump runs again then the leak in in the diaphragm inside
the pump. This happens when a pump has cycled too many times
and has worn out the diaphragm.

[Hib Halverson]

I'd say, you have a leak but not really a big one or the pump might have a somewhat restricted filter screen.

I just went out to the shop and checked the pump run time on my 95. After the initial run period, my aux. vac. pump runs for about a second every 15-20 seconds. I know my SPT system is in good condition. The SPT rule of thumb is, once the system is evacuated, one second every 15 seconds.

[Paul Workman]

Apples n Oranges??

When the LT5 performance is down, the question of the SPT system immediately comes under scrutiny, as it should - especially if a "61" occurs. However, for anyone following these "secondary" threads over the years, there is a tendency to proclaim AH-HA! prematurely! - pointing to the pump cycling as indicative of the problem being the SPT system when it isn't, regardless of whether it too needs to be serviced.

I think for the OP's benefit, the distinction to be made is between what is characteristic of a proper "tight" vacuum circuit vs. what the system will tolerate before causing an issue i.e., the SPTs not opening or throwing a "61" code.

Keep in mind the SPT is a closed circuit. So, if there were no leaks, even at WOT the pump wouldn't run but perhaps just long enough to replenish the initial reservoir vacuum expended to initially pull the actuators. So, barring any leaks, the pump would not run continuously - even at WOT.

Now, if there are some leaks, which typically there are (the many check valves, rubber connections, cracks, etc), the pump is there to maintain the vacuum...and shuts OFF when the necessary vacuum is reached - and will come back ON when before vacuum level is depleted to the point of jeopardizing the SPT system.

Marc's quick n dirty way to sort out the SPT comes from years of hands-on experience: specifically if the vacuum pump shuts off, even for a second, then one can assume there is sufficient vacuum, at least up to the secondary port throttle valve. He also discusses how to observe the actuators to verify their operation; verifying the circuit from the valve to and including the actuators (and vacuum can be monitored during that test as well.

The fine point missed (as I see it) in this/these discussion is NOT that the secondary circuit isn't perhaps in need of service - it could very well be. But! In the quest for locating a performance issue, one may be able to put the SPT system aside for latter attention while the real culprit is ferreted out. Make sense?

[scottfab]

Apples n Oranges??

....snip...

The fine point missed (as I see it) in this/these discussion is NOT that the secondary circuit isn't perhaps in need of service - it could very well be. But! In the quest for locating a performance issue, one may be able to put the SPT system aside for latter attention while the real culprit is ferreted out. Make sense?

I don't think this is a performance issue. At least reading the OP there is no indication of loss of power. The thread is about being confused. Getting apparently different or conflicting info.

Given that we're trying to clear it all up and not likely to get a consensus I'm sure the waters are now completely muddy. Oh well.

I see this whole "vacuum" issue as this.
You either have no issue with a leaking system
or you do. If you do you either decide to fix it
or let it go until you get a code 61.
Hey, but that's just me.

[XfireZ51]

It runs for only an instant...less than a second. Then, it stays off for 4 to 5 seconds. Then repeat.

Marc would say that it's operating properly. I was with him when looking at a stock ZR-1 that exhibited the same pattern. As long as the pump shuts off, the system is holding sufficient vacuum.

[KILLSHOTS]

I don't think this is a performance issue. At least reading the OP there is no indication of loss of power. The thread is about being confused. Getting apparently different or conflicting info.

Given that we're trying to clear it all up and not likely to get a consensus I'm sure the waters are now completely muddy. Oh well.

I see this whole "vacuum" issue as this.
You either have no issue with a leaking system
or you do. If you do you either decide to fix it
or let it go until you get a code 61.
Hey, but that's just me.
Exactly, Scott. My Z pulls like a freight train and idles smoothly at 800. Just trying to figure out how bad my leak is. Thanks for "boiling it down".

[Hog]

Hey Hog,

I was referring mainly to the PERCEPTION of when the big power comes on. As Marc says, with a 4:10 upgrade, "the really useful area begins at 3000 instead of 4000 RPM."

Chris
From Mr Haibecks site: "Has a broadening effect on the useful power band for the LT5. The throttle response is as good at 3000 rpm as it is at 4000 rpm with a 3.45 gear ratio"

So basically with stock gearing a downshift to 3rd gear may have been necessary to perform a passing manouver, with 4.10's, the same manouver can be performed in 4th gear.

Swapping to a lower gear increases torque multiplication to the wheels, enabling greater vehicle acceleration while engine output remains constant.

I understand what you mean.

xxxxxx
There would have been substantial engine vacuum with the LT5 throttle stopped at 70%. In addition to durability, other reason for the stop could be:
1)fuel economy
2) drivers right leg comfort, much easier to hold a pedal on a stop than holding against throttle spring tension

I do think that durability was certainly a concern, which is further evidenced by the decision to run a higher 3.07 ring/pinion. This would aid driveshaft, transmission, front accessory and engine durability, and again would aid fuel economy.

That record run was a great accomplishment.

[We Gone]

Another reason they used a 3.07 rear gear was to keep the RPMs under 6500 as the radiator was designed to bypass at higher RPMs due to higher water pressure. They had to keep it cool!!

[Paul Workman]

Another reason they used a 3.07 rear gear was to keep the RPMs under 6500 as the radiator was designed to bypass at higher RPMs due to higher water pressure. They had to keep it cool!!

And, too: does not the coolant pump begin cavitation just north of 5500 rpm?

Also, I read a comment (in Heart Of The Beast(?)) regarding the desire of limiting the rpm to place the LT5 in its peak torque region.

[RIP]

there also is a small vacuum switch inside the secondary pump, it could be out of adjustment and not shutting the pump off when vacuum is reached.

[weldbead]

i've had my '94 for less than a month and have very little time on the road with it..point being i dont know if my engine is at full power or not.. my pump ran for several minutes without shutting off when i tried it with key on but engine not running, i turned it off because it seemed longer than any other pump in the poll..real quick it says i have a bad leak or leaks.. would appreciate yer thoughts..

[We Gone]

Weldbead, I see its your first post Welcome... do a search here on it lots of posts on what and how to check it out. Sticky at top of this section.

http://www.zr1.net/forum/showthread.php?t=16778

[RIP]

Your engine produces the most vacuum at idol, and very little at full throttle, that's when the secondary pump goes to work. With engine off, key on, take the hose off the secondary pump and hold your finger over the outlet. Pump should stop. If it doesn't pump is bad or needs adjusted. You can check the rest of the system for vacuums leaks with a hand held vacuum tester, about $30 at sears. The system is not that completed.

[scottfab]

i've had my '94 for less than a month and have very little time on the road with it..point being i dont know if my engine is at full power or not.. my pump ran for several minutes without shutting off when i tried it with key on but engine not running, i turned it off because it seemed longer than any other pump in the poll..real quick it says i have a bad leak or leaks.. would appreciate yer thoughts..

That is the exact thing that happened to me when I bought mine.
You'll REALLY feel the difference when the leak is fixed.

Here is one of many vacuum leak troubleshooting sequences.
Click on the link below
Vacuum Leak Troubleshooting (http://www.zr1netregistry.com/Information/TechNet/%5BAllArticles%5D/tabid/262/articleType/ArticleView/articleId/51/Vacuum-Leak-troubleshooting.aspx)

[Dynomite]

As others have suggested close off the vacuum line closest to the pump with your thumb (after line is disconnected) and if the pump does not stop...bad pump or bad vacuum line connection to pump (hold thumb over pump connection to determine if bad pump). You can continue to use that some process to locate the leak if pump stops (for a minute or more) with the first line block with thumb.

Disconnect the lined further along and if pump stops (or cycles less), leak is beyond that line you just disconnected. Keep going and if pump does not stop (or cycles less) when you hold thumb over end of vacuum line, you have found the leak (or one of the leaks). Fix that leak and then continue disconnecting lines for possible additional leaks if pump does not stop once that leak is repaired and reconnected.

It is usual that the leak can be found at locations where fittings are easy to disconnect (Some of those connections are nearly impossible to disconnect....go past them as it would be unlikely the leak will be at that connection). With this method you can jump in anywhere and determine which direction to go if pump stops (or cycles less) to locate additional leaks. This will also locate the leak if found at the drivers side check valve which blocks the vacuum path to the plenum when plenum vacuum is low.

Once ALL significant leaks are found, the pump will stop cycling after initial vacuum is reached for a minute or more. At that point you are in business :thumbsup:

Before you pull the Plenum, check the pump and line going under the Plenum. Also check the Drivers Side vacuum line going into the Plenum at center of Plenum. The leak could be that Plenum connection or the check valve under the Plenum.

Checking for Vacuum Leaks TIPS (http://www.zr1.net/forum/showthread.php?p=187897)

[RIP]

Keep in mind, there is a vacuum switch inside the pump that can be adjusted.

[Dynomite]

there also is a small vacuum switch inside the secondary pump, it could be out of adjustment and not shutting the pump off when vacuum is reached.

How do you adjust that pressure/vacuum switch inside the vacuum pump?

Keep in mind, there is a vacuum switch inside the pump that can be adjusted.

What do you set the vacuum pressure at for proper vacuum?

[Schrade]

i've had my '94 for less than a month and have very little time on the road with it..point being i dont know if my engine is at full power or not.. my pump ran for several minutes without shutting off when i tried it with key on but engine not running, i turned it off because it seemed longer than any other pump in the poll..real quick it says i have a bad leak or leaks.. would appreciate yer thoughts..

Welcome onto the boards there. Post snappics of your Z there.


RIP - you see the adjuster here?

I did give a passing thought to what the controller mechanism was...

https://lh4.googleusercontent.com/-DuCwpowduM8/UoftiJMsXDI/AAAAAAAAC0A/UdOAT-Yh_R4/s1280/HPIM7531.JPG

[RIP]

When you draw a vacuum the small white piston in drawn in, separating the points and shutting the pump off. With a hand operated vacuum pump you should be able to see the points open and close. You could try to use your mouth. Suck, baby, suck.

[scottfab]

When you draw a vacuum the small white piston in drawn in, separating the points and shutting the pump off. With a hand operated vacuum pump you should be able to see the points open and close. You could try to use your mouth. Suck, baby, suck.

If the contacts are corroded they can be cleaned up with alcohol and covered with dielectric grease. If the pump runs for
ever it might be that
the diaphragm (in the round section of the pump) has a void in it.
It looks like this and is repairable using a rubber from a kitchen glove.

http://zr1.net/forum/picture.php?albumid=189&pictureid=1445

[weldbead]

seems most of the system is under the plenum..can someone tell me where to get fsm's?i need diagrams etc..thx..

[John Boothby]

ebay. Three manuals.

1. Field Service manual covers both standard and ZR-1.

2. LT-5 Supplement. Covers the LT-5 engine.

3. Electrical manual. Covers electrics.

Expect to pay $100 to $150 for all 3.

[Hib Halverson]

If the contacts are corroded they can be cleaned up with alcohol and covered with dielectric grease. (snip)

Now, Scott...
:)
...don't you know alcohol is for drinking and "contact cleaner" is for cleaning electrical connections.

[Hib Halverson]

Another reason they used a 3.07 rear gear was to keep the RPMs under 6500 as the radiator was designed to bypass at higher RPMs due to higher water pressure. They had to keep it cool!!

And, too: does not the coolant pump begin cavitation just north of 5500 rpm?

Also, I read a comment (in Heart Of The Beast(?)) regarding the desire of limiting the rpm to place the LT5 in its peak torque region.


Guys, guys...maybe we're "overthinking this"?

The Record Run took place on 1-2 March 1990. Ever been to central TX in March? At night, it's freakin' cold...in the high-20s. Plus, during the 24-hr period the RR was staged, it snowed and rained. At start time on 1 March it was 35°F. Cooling was not an issue because 1) the low ambient and 2) since the engine was running at only part throttle, cooling load was reduced.

Limiting RPM to place the LT5 at peak torque, regardless of what Heart of the Beast may say, was not an issue, either. Besides, with a throttle stop, the engine was not making peak torque, anyway.

The main reasons for the throttle stop were 1) fuel mileage and range, 2) durability and 3) ensuring drivers would not exceed a TPS value which would compromise 1 and 2.

[Hib Halverson]

ebay. Three manuals.

1. Field Service manual covers both standard and ZR-1.

2. LT-5 Supplement. Covers the LT-5 engine.

3. Electrical manual. Covers electrics.

Expect to pay $100 to $150 for all 3.

I think the car in question is a 94.
The Factory Service Manual set for a '94 has only two volumes covering both VIN P and VIN J (LT5) engines. I've seen them on eBay but, also, Zip Products stocks Service Manuals, and they're the real thing not reprints or scans. In recent years, I've been getting my manuals from Zip. See this web page
(http://www.zip-corvette.com/catalog/product/view/id/7135/s/94-shop-service-manual/category/8411/)

[Paul Workman]

Guys, guys...maybe we're "overthinking this"?

The Record Run took place on 1-2 March 1990. Ever been to central TX in March? At night, it's freakin' cold...in the high-20s. Plus, during the 24-hr period the RR was staged, it snowed and rained. At start time on 1 March it was 35°F. Cooling was not an issue because 1) the low ambient and 2) since the engine was running at only part throttle, cooling load was reduced.

Limiting RPM to place the LT5 at peak torque, regardless of what Heart of the Beast may say, was not an issue, either. Besides, with a throttle stop, the engine was not making peak torque, anyway.

The main reasons for the throttle stop were 1) fuel mileage and range, 2) durability and 3) ensuring drivers would not exceed a TPS value which would compromise 1 and 2.

RE: peak torque at the Record Run (RR):

Well, of course the motor wouldn't be making max torque with the throttle stop, compared to WOT. But, rather I was referring to the shape of the torque curve, i.e., where the torque azimuth occurs, assuming no significant change in the curve, regardless of throttle being at 70% vs. 100%.

I refer to one of many graphs I can produce which share the same general torque curve shape as the one (below). Notice the torque reaches azimuth around 5200 rpm for this particular motor - which forms the basis of my comment. (Note: This happens to be a modded motor, but I can produce several graphs - all having very similar curve characteristics if need be.)

http://i185.photobucket.com/albums/x220/6PPC_bucket/Dyno%20graphs/LT5ptopenvsclosed_zps79a8b9ce.jpg (http://s185.photobucket.com/user/6PPC_bucket/media/Dyno%20graphs/LT5ptopenvsclosed_zps79a8b9ce.jpg.html)

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/ZF6MPH345vs410gearratio-Haibeck_zps837f03ef.jpg (http://s185.photobucket.com/user/6PPC_bucket/media/tech%20files/ZF6MPH345vs410gearratio-Haibeck_zps837f03ef.jpg.html)

Considering the 3.07 differential affect on speed vs. rpm for a stock diff gear: 3.07/3.45 = rpm factor = 0.8899. By multiplying the rpm for a stock ZR-1 (5th gear) required for speed close to the average of the Record Run (6000 rpm ≈ 177 mph from the chart (c/o Haibeck Automotive)), the result is (6000 x .8899) = 5339 rpm w/ the 3.07 differential gear. That's purdy dang close to the peak torque value. Just a coincidence? :icon_scra If Young didn't quote someone for his "HEART OF THE BEAST", he at least did the math, I recon.;)

[Hib Halverson]

What's a "torque azimuth"?

In your calcs, did you figure tire size?

The RR speed (175.885) was an average so the speeds on the track were faster. About 190 at corner entries or about 5500RPM in fifth gear. The car had slowed to about 170 at corner exits.

[Paul Workman]

What's a "torque azimuth"?

In your calcs, did you figure tire size?

The RR speed (175.885) was an average so the speeds on the track were faster. About 190 at corner entries or about 5500RPM in fifth gear. The car had slowed to about 170 at corner exits.

Guys, guys...maybe we're "overthinking this"?
...

"Apex" would have been a better choice than azimuth, my bad; peak torque, to be clear...is the point.

With that cleared up, my point is/was choosing a 3.07 differential gear would obviously put the LT5 rpm right in the sweet spot of the torque curve; with the LT5 passing through the peak of the curve on every lap and remaining near the peak most of the time.

As for tire size, if the tires were not the stock 315x35x17 size, then the results would be skewed more or less, depending on the amount of departure the tires used on the Run were from the stock tire size. (What were the tire make/model/size used on the Run?)

So, it strikes me that choosing the 3.07 ratio for the differential, resulting in the motor operating near peak torque the whole time (in 5th gear) was not accidental, but a major consideration - along with limiting motor output for all the reasons you mentioned.

[Hib Halverson]

The tires were not stock.

They were Goodyear Racing Eagles which were made specifically for the Record Run. I can't remember the size. I'll have to do some digging to see if I still have that information.

And yeah, the 3.07 axle was selected so the car could run 190 mph in fifth gear. As for if that was the optimal ratio? Maybe not but the 3.07 was the tallest ratio available for a D44 in a Corvette. The 2.73 and 2.59 ratios for D36 gearsets.

[Paul Workman]

The tires were not stock.

They were Goodyear Racing Eagles which were made specifically for the Record Run. I can't remember the size. I'll have to do some digging to see if I still have that information.

And yeah, the 3.07 axle was selected so the car could run 190 mph in fifth gear. As for if that was the optimal ratio? Maybe not but the 3.07 was the tallest ratio available for a D44 in a Corvette. The 2.73 and 2.59 ratios for D36 gearsets.

I'm intrigued by the details, as you seem to be too... (Probably because my favorite TV program was "Mr Wizzard", or maybe because I have a 'low entertainment threshold', or as some have said ... "You're easily amused" - referring to me: never quite sure how to take that:icon_scra).

But, yeah! Actual tire metrics would be interesting, and I agree the 3.07s were available, perhaps more so than what would be exactly perfect for the "task at hand". Any way ya slice it, the RR was a fascinating moment in automotive history, regardless.

:cheers:

[Hib Halverson]

Since 1990, I've written several articles on the Record Run for different magazines and web sites.

The tires size was not in the last two stories I did, but a search of pre-2000 manuscripts and, finally, found it.

The tires were special race radial race tires done by Goodyear just for that program and the size was 25.5x12.0-17. That tire was used at all four corners on both cars.

[weldbead]

(small)progress update..my fsm's have arrived, i've done a bit of reading there and here..have opened the first connection in the pump suction line (which is just a coupling..why is it there, iwonder..) and with it thumbed off the pump stops instantly, telling me there is a leak downstream which is under the plenum unless its map hose ..so i'm starting to think i'm gotta remove the plenum..
symptomatically :key on engine off pump runs forever..there are times when i punch it and really feel a power surge at 3000 rpm or so, and there are times when i dont..also there are times when i punch it and i think the secondaries are open, and then it peters out and wont get over 5500 rpm so i guess the secondaries have gone closed as vac drops and pump cant keep up..