Secondary Vacumm Pump question???

[Roadster]

I have noticed that the Secondary vacumm pump under the right headlight assembly has been disconnected. Therefore the pump was never running. When I plugged it back in, the piump runs continuously. So with that thought in mind:
1-why and would the seconandaries operate?
2- is it safe to assume that the pump needs replacement, or am I missing something here in the way the system functions ?

Again, the engine runs great, and that first complete WOT was nothing short of amazing. And I would also assume that the secondaries are operational, as there is no reason to believe that they were ever disconnected, unless that was performed when GM Engineering owned the Vette for the first 2 years.
From my research on previous owners, it seems that not too many parts were replaced. And the latest fuel filter and spark plugs were changed within the last two thousand miles.

PS....I don't have any stumble or hesitation what-so-ever, when you press down on the accelerator, it is an instant response throughout the gears.

Still learning about everything, so any thoughts or info is appreciated.
Thanks...........................

[Dynomite]

Secondary Functional Test and Reconditioning the Secondary Actuators TIPS (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-4.html#post1581665189)

Sounds like you have your secondary system removed. Someone then just disconnected the pump. Look down between the runners of the Plenum as shown in in the link and you should be able to see the secondary actuator arms (one each side). Also...do you see a vacuum line leading from the vacuum pump up and under the Plenum on the passenger front of the engine?

It seems to me that you would loose vacuum at Wide Open Throttle as Plenum Vacuum would drop and the secondaries would then close if they existed given the vacuum pump is disconnected. If you have the secondaries intact, and a complete vacuum system, you definitely have a BIG vacuum leak under the Plenum. The Secondary Functional Test would FAIL under the conditions you have unless the vacuum pump is JUST able to maintain Secondary Vacuum by running constantly.

Is the Vacuum Connection between the two runners on the Drivers Side of the Plenum blocked? If so...that would also indicate the Secondaries have been removed.

If you have a BIG leak in the Vacuum system you are out of luck under ALL conditions operating the secondaries. There is a vacuum check valve under the Plenum which holds vacuum provided by the pump when plenum vacuum is low...that check valve does not function the other way...holding vacuum when the vacuum pump is non functional.

Vacuum provided by the Drivers Side of the Plenum will allow the Secondaries to function under some conditions but once Plenum Vacuum drops you are out of luck with the Secondary Operation.....I am thinking.

[Roadster]

Cliff, thank you for your link, will try to get that done by the end of the day.:)

[efnfast]

Does the engine rev to 7K?

[Roadster]

Does the engine rev to 7K?

Yes it sure does, and mighty quickly at that. It seems like it wants to climb the rpm range forever.......:-D

And again, no stumbles or anything like that and when you pull a shift, it just climbs where it left off......

I am very satisfied with the way that it runs, that WOT really made my eyeballs bigger......it was like I never imagined the full power this motor has....

[efnfast]

I'm no expert here, but I don't think the secondaries will open at all without the vacuum pump. And if it's revving to 7K, we can assume the secondaries aren't there?

[Kevin]

I'm no expert here, but I don't think the secondaries will open at all without the vacuum pump. And if it's revving to 7K, we can assume the secondaries aren't there?

sounds like a logical assumption. If you're running fine without them don't put them back in

[Roadster]

I'm no expert here, but I don't think the secondaries will open at all without the vacuum pump. And if it's revving to 7K, we can assume the secondaries aren't there?

sounds like a logical assumption. If you're running fine without them don't put them back in

It all makes sense, I am going out to the garage right now and check out some of the items Cliff pointed out in his post.
I guess I woiuld be totally surprised if they are removed......

Ok, I know alot of owners have removed the secondaries, does the engine run that much better with them eliminated? Just curious on that!!!

[Roadster]

Secondary Functional Test and Reconditioning the Secondary Actuators TIPS (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-4.html#post1581665189)

Sounds like you have your secondary system removed. Someone then just disconnected the pump. Look down between the runners of the Plenum as shown in in the link and you should be able to see the secondary actuator arms (one each side). Also...do you see a vacuum line leading from the vacuum pump up and under the Plenum on the passenger front of the engine?

Is the Vacuum Connection between the two runners on the Drivers Side of the Plenum blocked? If so...that would also indicate the Secondaries have been removed. [/B]

Ok after further investigation, I am now assuming that the secondaries are non-exsistent.....
1-pump was and has been disconnected. and from what I am trying to understand, is that with the pump being disconnected, there would be no way that the secondaries would be functional at all, is that a correct assumption???
2-looking down between the runners on each side, I do not see the secondary actuator arms at all. it just looks like an open space on each side.
3-the vacuum line is still connected from the pump and goes under the plenum on the passenger front of the engine, but it feels looser than it should under the plenum.
4-that vacuum connection between the two runners on both sides of the motor are still connected.
5-so I imagine that the secondaries could be eliminated, but everything was not removed in the process.....

[KILLSHOTS]

Ok after further investigation, I am now assuming that the secondaries are non-exsistent.....
1-pump was and has been disconnected. and from what I am trying to understand, is that with the pump being disconnected, there would be no way that the secondaries would be functional at all, is that a correct assumption???
2-looking down between the runners on each side, I do not see the secondary actuator arms at all. it just looks like an open space on each side.
3-the vacuum line is still connected from the pump and goes under the plenum on the passenger front of the engine, but it feels looser than it should under the plenum.
4-that vacuum connection between the two runners on both sides of the motor are still connected.
5-so I imagine that the secondaries could be eliminated, but everything was not removed in the process.....
If you can redline the car with the pump disconnected, then your secondaries are removed. If they were intact, you'd have a hard time revving past 5000. Just turned off my key and confirmed that about an hour ago.

[Schrade]

Some 2nd vac pump breakdown / diags snappics here, starting post #346 http://www.zr1.net/forum/showthread.php?t=21439&page=9

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

[Dynomite]

I'm no expert here, but I don't think the secondaries will open at all without the vacuum pump. And if it's revving to 7K, we can assume the secondaries aren't there?

You get vacuum from two sources for secondary operation (Vacuum pump and Plenum). There is a check valve that opens when plenum vacuum takes over. When the Vacuum pump is working that check valve is closed such that the Vacuum pump does not start evacuating the Plenum.

Secondary port vacuum diagnosis TIPS (http://www.corvetteactioncenter.com/forums/c4-corvette-zr-1/14272-1990-1995-zr-1-secondary-port-vacuum-diagnosis.html)

http://www.corvetteactioncenter.com/tech/c4/zr1/images/lt5graph.jpg

[Roadster]

If you can redline the car with the pump disconnected, then your secondaries are removed. If they were intact, you'd have a hard time revving past 5000. Just turned off my key and confirmed that about an hour ago.

Hey, Chris, thanks for the confirmation on that.....:-D
Still in the learning process with all of this, had no idea or reason to believe that the secondaries could or would be eliminated on my 94. And yes as stated before it does make sense that if the secondaries were in tact and the pump disconnected that the engine would not run as good as it does.
Now I need to find out who removed them and when.....hmmmmm!!!

[Dynomite]

Hey, Chris, thanks for the confirmation on that.....:-D
Still in the learning process with all of this, had no idea or reason to believe that the secondaries could or would be eliminated on my 94. And yes as stated before it does make sense that if the secondaries were in tact and the pump disconnected that the engine would not run as good as it does.
Now I need to find out who removed them and when.....hmmmmm!!!

No.....you need to find out who clobbered up the Secondary removal and remove the plenum and do it right :D
Also.....you might have a modified chip to account for secondary removal......;)

If you can redline the car with the pump disconnected, then your secondaries are removed. If they were intact, you'd have a hard time revving past 5000. Just turned off my key and confirmed that about an hour ago.

It appears that you do not have functional secondaries....and possibly someone removed the secondary function without removing the whole secondary system (tying the secondaries open for example and leaving all the vacuum lines in place).

[Roadster]

No.....you need to find out who clobbered up the Secondary removal and remove the plenum and do it right :D
Also.....you might have a modified chip to account for secondary removal......;)

I kow that some day I will have to pull the plenum and yes, do it right....

If you might remember I had the Tim Holland Chip in there from the early GM engineering days of ownership. I then ordered a chip from Marc, and of course at the time had no idea that my secondaries might be eliminated. The main reason I went with the chip was to get the fans to come on & off at the lower temps. So Marc's chip that is in there now, does not have any provisions for secondary removal. And I know I keep repeating myself, but it runs great.....
I have noticed some oil around a Torx screw or two, especially around number 1 cylinder, so I need to snug those down.
Actually I need to retire to keep up with my vehicles, but I am a few years away from that. I'll just wait until the colder weather before I do a pull, did receive my DVD from Marc and with your links and people who have done it already, hopefully it won't be complicated once I get into it.
And being in the area of the WAZOO gang, maybe I can hook-up with them sometime in the future whenever they do a Plenum pull day.......:-D

[Roadster]

Some 2nd vac pump breakdown / diags snappics here, starting post #346 http://www.zr1.net/forum/showthread.php?t=21439&page=9

Thanks for the pic and link, some serious reading there for sure, it is bookmarked for future use......:-D

[Roadster]

If you can redline the car with the pump disconnected, then your secondaries are removed. If they were intact, you'd have a hard time revving past 5000. Just turned off my key and confirmed that about an hour ago.

Ok Chris, you got me in the mood, did my second complete WOT minutes ago (deserted road, no one around) out of 1st gear on a slight roll, looks like I shifted around 7200 r's just slightly above the 7k marking on the tach. Just unbelievable, I could do that all day long. Not a hiccup, just pure LT5 engine power....Coolant Temp @ 204* Oil Temp @ 208* fully warmed up motor....vacuum pump disconnected as usual, apparently no secondaries to be found......:dancing

[KILLSHOTS]

Ok Chris, you got me in the mood, did my second complete WOT minutes ago (deserted road, no one around) out of 1st gear on a slight roll, looks like I shifted around 7200 r's just slightly above the 7k marking on the tach. Just unbelievable, I could do that all day long. Not a hiccup, just pure LT5 engine power....Coolant Temp @ 204* Oil Temp @ 208* fully warmed up motor....vacuum pump disconnected as usual, apparently no secondaries to be found......:dancing
There's the Permagrin!

[Roadster]

There's the Permagrin!

You got that right......:-D:-D:-D

[weldbead]

No.....you need to find out who clobbered up the Secondary removal and remove the plenum and do it right :D
Also.....you might have a modified chip to account for secondary removal......;)



It appears that you do not have functional secondaries....and possibly someone removed the secondary function without removing the whole secondary system (tying the secondaries open for example and leaving all the vacuum lines in place).

what would be the down side of physically tying the butterlies open but leaving the the ailing vacuum system alone?

[Dynomite]

what would be the down side of physically tying the butterlies open but leaving the the ailing vacuum system alone?

Not much except removing the secondary butterflies gives you totally unrestricted air. And the logic for secondary
Injector firing should be changed. I have no clue why one would leave stuff not used in the valley.

[Roadster]

what would be the down side of physically tying the butterlies open but leaving the the ailing vacuum system alone?

Not much except removing the secondary buttrrflies gives you totally unrestricted air. And the logic for secondary
Injector firing should be changed. I have no clue why one would leave stuff not used in the valley.

Other that what Cliff has mentioned above, it seems like they were just lazy with that particular function. On a side note, the PO did mention that this was the best running ZR-1 that he owned. He add 2 others before this one, a 91 and I think a 95, he really liked the way it performed, but he was hot on the trail for a Cobra Replica car, so the 94 had to go.

[Hog]

I would be interested to see the complete torque curve difference between installed but non-functioning port throttles compared to completley dissected port throttles.