Failed secondary system? Where to start?

[Athens91ZR1]

Hello all,

I am new to this forum and am helping a family friend (original owner) get their 91 ZR-1 ready to sell. The car only has 24k original miles and is 100% stock.

Current Situation:

The car drives beautifully in the Normal engine mode but when turning the key to the Full engine mode, it falls flat on its face and it feels as though the ECU is more or less preventing the car from accelerating at all (too lean or too rich of an air/fuel mixture I am guessing). I am aware of the injector issues that the early years had due to ethanol content and the owners are saying that they had the injectors replaced about 10 years ago. But I am still skeptical about how good of a job the previous mechanic did installing them.

Where should I start to diagnose this issue? (I am mechanically inclined and have an E85 converted 3000GT VR-4 that people say is a hard car to work on so am not afraid to take off the plenum if need be and/or take on a new challenge to fix this ZR-1 for its next rightful owner).

Thank you for all the help and tips, in advance! Oh and if anyone in Colorado is looking for a great condition ZR-1, then message me to come check out the car.

Jordan

[Z51JEFF]

First check to see if the vacuum pump for the secondary’s is working,with the car off turn the key on to power the pump,you will hear it run for a short cycle then go off,this will repeat. You can also unplug the vacuum pump line at the connector by the ALTERNATOR,it will run constant. What type of injectors were used for the replacement?

[dredgeguy]

What are the colors or the car? Suggest you post up with some pics in the for sale section as people are always looking and might be interested in it as is.
Good luck

[Paul Workman]

"Jeff" is spot-on.

And, a good place to start is Marc Haibeck's (http://www.zr1specialist.com/) troubleshooting article(s) on his ZR1 Specialist web site. It is quite comprehensive.

That said, usually, secondary port throttle (SPT) operation failure is easy to run down. Most of the problems stem from age of the vacuum harness components. And, the good news is ALL of the stuff is available from Jerry's Gaskets (http://www.jerrysgaskets.com/).

And, then there's fuel pressure* to consider: 45 psi at light throttle to 53-55 psi at WOT. Check for normal [4-5 amperes each for 8-10 amperes total] current to the diagnostic connector (with the ignition switched OFF).

*NOTE: If the fuel filter (next to the frame rail behind the right front tire) is partially blocked, it may not affect normal driving (i.e., lo throttle %). Only when going to WOT does fuel pressure fall way below the 53-55 psi range.

Fuel pressure regulator affects pressure too, but unlikely considering the mileage being so low. Just "tuck" that away for now.

NEVER ASSUME! TRUST ME.... Just because something was replaced, that in and of itself is no proof of normalcy. I'm speaking from experience with regard to those injectors: you'll need to verify uniform resistance across them when at normal operating temperatures. (A reading of either 12Ω ± 1 or 14Ω ± 1 is normal. But, a reading beginning at 10Ω is indicative of impending doom. A reading of 8Ω or less assures failure is well on its way and the entire lot needs to be replaced.

We can get into more specifics if needed. But, first getting some of the preliminary fundamental stuff (AIR-FUEL-SPARK) evaluated will point in the direction for the in depth stuff.

[Athens91ZR1]

The car is Polo Green Metallic and I believe it is called saddle leather interior (kind of a beige). What do you guys feel is a fair listing price, based on the low mileage (24k miles)?

I should be able to post photos by next week.

[Ccmano]

Here you go... this will walk you though it.
http://www.zr1specialist.com/HAT%20Web/articles/Are%20The%20Secondaries%20Working.pdf

As noted could also be a bad secondary fuel pump.
H
:cheers:

[Athens91ZR1]

Thank you, H!

I will verify all the steps you and others have provided, starting this weekend. Since it is a 91, the Full Power lamp should still be showing up on the driver's information panel if it is working, correct?

I think I remember only seeing the green light lighting up near the valet key...

[Z51JEFF]

Thank you, H!

I will verify all the steps you and others have provided, starting this weekend. Since it is a 91, the Full Power lamp should still be showing up on the driver's information panel if it is working, correct?

I think I remember only seeing the green light lighting up near the valet key...

90 was the only year with the full power showing in the panel,91 only has the small green light by the switch.

[Athens91ZR1]

Are the spark plugs easy to check while I am in under the hood? Any tips from experts or special extensions/special tools needed?

[Ccmano]

The plugs are all relatively easy with various extensions except #8 (pass side at firewall). With the right combination of socket and extensions it’s not too bad. A magnetic spark plug socket with an intergral swivel and wobble extensions makes it easy without removing the blower cover. There is also a good write up here.
H

http://www.zr1.net/forum/showthread.php?t=27581&highlight=spark+plug


http://a65.tinypic.com/2imb2py.jpg

[lfalzarano]

It’s easy as he said with the right flex connections. Before removing each plug, with an air compressor, blow out any potential debris before removing the plug .


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[Top Toy]

It likely still has the accordion bellows in the air intake. These get soft with age and will collapse at WOT. If it feels soft, remove it for a test run to see if that makes a difference.

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[Paul Workman]

It likely still has the accordion bellows in the air intake. These get soft with age and will collapse at WOT. If it feels soft, remove it for a test run to see if that makes a difference.

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Good catch! Shoulda mentioned that.:thumbsup:

[Mystic ZR-1]

Bellows get soft with age?
I’m sure age doesn’t help, but I remember
seeing ZR-1s at the dragstrip in 1990 with
these hoses collapsing...
Marc has the solution.

[Athens91ZR1]

It likely still has the accordion bellows in the air intake. These get soft with age and will collapse at WOT. If it feels soft, remove it for a test run to see if that makes a difference.

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Any chance you have a picture of this accordion bellows? Is it easy to access?

[A26B]

It is located between front of the Throttle Body Extension (Air Horn) & the black, plastic air filter housing. Clamps on each end.

https://cdn10.bigcommerce.com/s-nkg90o/products/858/images/1980/14104557-NOS__55864.1463459748.1280.1280.jpg?c=2

[Athens91ZR1]

Update from today:

1) All 8 spark plugs replaced with AC Delco coppers and gapped to 0.042" (car starts and idles much better now)
2) Verified that the secondary port vacuum pump is working as designed
3) Used handheld vacuum pump and found no leak on the pump side of the inline connector but a very small leak appears to be present on the connector side (maybe a tiny leak under the plenum?)
4) Shorted pins A and B on the OBD connector with a paper clip and found code 61 present
5) Accordion bellows seems to be in fine shape (not soft and doesn't feel like it would be collapsing)

Questions:

1) Should I do the ECM check that Marc outlines by grounding connector C17 to test the secondary throttle actuators or pull the plenum now?
2) Where is the ECM located (I am assuming under the dash somewhere?)?
3) Anything special I need to know about removing the plenum? Do I need to drain any fluids first?

Thank you!
Jordan

[Dynomite]

ECM is under hood right in front of driver.
Yes.....drain coolant to a level below injector housings.
You will need two Plenum gaskets from Jerry :thumbsup:

Left click on items in my signature for Plenum Pull :thumbsup:
Second item has several Plenum Removals described in detail.
If you have not pulled Plenum before, I would leave it be as the Secondaries will function perfectly even with a small vacuum leak.

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[Athens91ZR1]

ECM is under hood right in front of driver.
Yes.....drain coolant to a level below injector housings.
You will need two Plenum gaskets from Jerry :thumbsup:

Left click on items in my signature for Plenum Pull :thumbsup:
Second item has several Plenum Removals described in detail.
If you have not pulled Plenum before, I would leave it be as the Secondaries will function perfectly even with a small vacuum leak.

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Hell...YES! Thank you very much for the in-depth write up!

If you had to guess, how much coolant should I have to drain out before pulling the plenum?

[Dynomite]

Hell...YES! Thank you very much for the in-depth write up!

If you had to guess, how much coolant should I have to drain out before pulling the plenum?

A gallon more or less......as you lift the plenum if there is any coolant around....drain a bit more coolant. The less coolant drained the better as you will not create air pockets the less coolant you drain.

[Athens91ZR1]

Please correct me if I am wrong, but at this point, I will absolutely have to pull the plenum since I am throwing a code 61 and no vacuum leaks are present outside of the plenum, correct?

According to Marc's write up, the only thing left that it can be is the secondary vacuum actuators not receiving enough vacuum (< 6 in. Hg) right?

[Dynomite]

Please correct me if I am wrong, but at this point, I will absolutely have to pull the plenum since I am throwing a code 61 and no vacuum leaks are present outside of the plenum, correct?

According to Marc's write up, the only thing left that it can be is the secondary vacuum actuators not receiving enough vacuum (< 6 in. Hg) right?

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

[Athens91ZR1]

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


I have followed this link and that is what got me to where I am today. What would cause a code 61 to throw if no vacuum leaks appear to exist? Only the actuators under the plenum, right?

[Dynomite]

There exists several vacuum connectors under the Plenum which are usually hardened and leaking with age in addition to a vacuum reservoir and vacuum solenoid control valve and actuators.

[Athens91ZR1]

There exists several vacuum connectors under the Plenum which are usually hardened and leaking with age in addition to a vacuum reservoir and vacuum solenoid control valve and actuators.


Thank you! But all require me to remove the plenum to diagnose right?


And when I ground the C17 connector on the ECM, I should hear and see the linkage moving right? That is all that is testing?

[Dynomite]

Thank you! But all require me to remove the plenum to diagnose right? Yes


And when I ground the C17 connector on the ECM, I should hear and see the linkage moving right? That is all that is testing? Yes

Post 234 - Installation of New Secondary Port Vacuum System Lines (https://www.corvetteforum.com/forums/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-12.html#post1590759176)

[Athens91ZR1]

Your guide and write-ups are amazing and thank you for all the time and energy you put into them!

Do you have a section specifically for plenum removal by chance? I see the "Four Minute Plenum Installation" but would love it if you had a plenum removal by chance.

[Dynomite]

Post 63 - Removing Plenum (including the 10 minute Plenum Removal) (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-4.html#post1581663365)

First.....drain coolant level down a bit to level of injector housing.

[Z51JEFF]

If you do pull the plenum there are a few tips to help in the process. While unplugging-plugging the ignition module from the front,prop the plenum up with something as you will need both hands to get the plugs loose from the ignition module. At the back of the ignition module there is a multi pin connector with 2 6? MM bolts,one on each end. Cars should be taken when plugging this back in as it is very easy to bend the terminals. Upon reassembly pay close attention to the CORKSCREW shaped vacuum line that goes down into a rubber connector,it’s easily comes out and you won’t know it until you start the car and have a vacuum leak. What I’ve done with this vacuum line in I’ll seat the end of the line in the connector,wrap a piece of tape around the exposed area and watch this as I drop the plenum.

[Athens91ZR1]

If you do pull the plenum there are a few tips to help in the process. While unplugging-plugging the ignition module from the front,prop the plenum up with something as you will need both hands to get the plugs loose from the ignition module. At the back of the ignition module there is a multi pin connector with 2 6? MM bolts,one on each end. Cars should be taken when plugging this back in as it is very easy to bend the terminals. Upon reassembly pay close attention to the CORKSCREW shaped vacuum line that goes down into a rubber connector,it’s easily comes out and you won’t know it until you start the car and have a vacuum leak. What I’ve done with this vacuum line in I’ll seat the end of the line in the connector,wrap a piece of tape around the exposed area and watch this as I drop the plenum.

Thank you for the tips! Always love to hear tricks like this. I plan to start removing the plenum this weekend and will update all, along the way.

[A26B]

......................................At the back of the ignition module there is a multi pin connector with 2 6? MM bolts,one on each end. Cars should be taken when plugging this back in as it is very easy to bend the terminals. .............................................

Just so the OP doesn't go crazy looking for 2 bolts :-D for the connector on the rear of the Ignition (a/k/a DIS) module, there is only one bolt, right in the center, which is 1/4" hex size.

Jeff is right on about being careful not to bend one of the pins while reconnecting. Most of us have experienced that problem. :cheers:

[secondchance]

Just so the OP doesn't go crazy looking for 2 bolts :-D for the connector on the rear of the Ignition (a/k/a DIS) module, there is only one bolt, right in the center, which is 1/4" hex size.

Jeff is right on about being careful not to bend one of the pins while reconnecting. Most of us have experienced that problem. :cheers:

Plus, at least for later cars, another weatherpak connector left of ignition module pin connector.

[Athens91ZR1]

I finally got around to starting the diagnostic....

When I ground ECM pin C17, the secondary pump runs continuously and it sounds like air is just leaking under the plenum and can’t see the linkage moving. I’m guessing I have a leak under the plenum.

Is this a correct diagnosis?

[-=Jeff=-]

Sound correct based on your description

[Paul Workman]

Just some tips (I found useful) on pulling the plenum and troubleshooting vacuum harness:


Have a replacement plenum gasket (from Jerry's Gaskets) on hand.

lay the new gaskets on a table (flat surface) and apply a wetting of silicon spray to the upper surface of the gasket (ONLY) before installing the gasket. (This will facilitate easy removal of the plenum w/o damaging the gasket, should you ever have to pull the plenum again. That way you can loosen the bolts and slide a thin putty knife between the plenum and the IH - thus separating the plenum so it can be lifted off. I have been able to reuse the gasket after twice more pulling the plenum w/o having to replace the gasket.)

By either bypassing the throttle body (TB) OR plugging the coolant passages to the TB "while you're in there", the next time you have to pull the plenum you won't have to drain coolant first, or replace it after. Then, removing the plenum takes under 10 minutes...FIVE if you're in a hurry!

Using a hand vacuum pump connected to the harness will lead you to the trouble quickly. Jerry's has everything you might need to overhaul the entire vacuum circuit.

Or...you might want to consider removing the entire Secondary Port Throttle (SPT) apparatus (a re-programmed chip is required to do so) and NEVER miss it...EVER! (Just sayin...) [You have the option of reversing the SPT removal, or forever eliminating it. Parts that don't exist don't break, and they don't cost much!]

[Athens91ZR1]

Just some tips (I found useful) on pulling the plenum and troubleshooting vacuum harness:

Have a replacement plenum gasket (from Jerry's Gaskets) on hand.
lay the new gaskets on a table (flat surface) and apply a wetting of silicon spray to the upper surface of the gasket (ONLY) before installing the gasket. (This will facilitate easy removal of the plenum w/o damaging the gasket, should you ever have to pull the plenum again. That way you can loosen the bolts and slide a thin putty knife between the plenum and the IH - thus separating the plenum so it can be lifted off. I have been able to reuse the gasket after twice more pulling the plenum w/o having to replace the gasket.)
By either bypassing the throttle body (TB) OR plugging the coolant passages to the TB "while you're in there", the next time you have to pull the plenum you won't have to drain coolant first, or replace it after. Then, removing the plenum takes under 10 minutes...FIVE if you're in a hurry!
Using a hand vacuum pump connected to the harness will lead you to the trouble quickly. Jerry's has everything you might need to overhaul the entire vacuum circuit.
Or...you might want to consider removing the entire Secondary Port Throttle (SPT) apparatus (a re-programmed chip is required to do so) and NEVER miss it...EVER! (Just sayin...) [You have the option of reversing the SPT removal, or forever eliminating it. Parts that don't exist don't break, and they don't cost much!]



Thank you very much for the tips! I have the handheld vacuum pump and plan to use that to isolate the leak.


As far as the gasket, do you have the link to the exact one(s) I need from Jerry's Gaskets?


Is this the correct one to get? (The car is 100% stock and still has the coolant passage to the TB).
http://www.jerrysgaskets.com/gasket-set-intake-plenum-1-32-90-95-7-5d2/

[G8nightman]

Yes that is the gasket.

[Paul Workman]

Thank you very much for the tips! I have the handheld vacuum pump and plan to use that to isolate the leak.


As far as the gasket, do you have the link to the exact one(s) I need from Jerry's Gaskets?


Is this the correct one to get? (The car is 100% stock and still has the coolant passage to the TB).
http://www.jerrysgaskets.com/gasket-set-intake-plenum-1-32-90-95-7-5d2/

You can go on-line at Jerry's Gaskets (http://www.jerrysgaskets.com/) and order a pair (or two) of plenum gaskets. Just provide the model year and Jerry will fix you up! And, if you didn't know, Jerry supplies most all of the LT5 parts, etc too: not just gaskets.

[Athens91ZR1]

Code 61 is now cleared! A semi melted plastic vacuum line was the culprit.

Unfortunately now the car is throwing a code 55 (lean condition, right?). What are the best places to start on that diagnostic?

Again, thank you so much for all the advice thus far. I cannot thank you all enough!

[A26B]

First, clear all the codes by battery disconnect for a couple of minutes. A lean code could be the result of a vacuum leak now resolved & you are seeing an old code.
After clearing stored codes, drive & see if any codes appear. If there are new codes, start with resolving the lowest numerical code first (except for 12)



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