1990 ZR-1 Hesitation when full Power

[frantinoro]

List of replaced parts:
Both fuel pumps
Spark plugs
o2 sensors

Hello,
Been chasing an issue with my new 1990 ZR-1. When I first bought it the full power key did nothing, and I found out I had an intake gasket leak, which filled 2 of the secondaries with coolant. Once that was fixed, I was having a misfire, and found that out to be a hefty sized vacuum leak, and then driving the car got gradually better. According to the PO, coils have been replaced, injectors, plug wires, and the accordion with a solid one.

Now, when in full power mode ONLY, the car vibrates like crazy and noticeably loses power until around 3-4k rpm (I am assuming - the tach is innacurate), and even then, the vibration just minimizes - it still feels like it has more power left. It has a "tune" apparently, I have no information on it, so I ordered a tune from ZR1specialists just for peace of mind. Any suggestions on what to test?
Thanks,
Francesco

[Young1]

Has the function of the secondaries been tested? I suspect they are not opening smoothly and fully. This can cause a rich condition for lack of air to mix with the fuel. Also the injectors may have been compromised by the coolant that filled the 2 secondaries. The following is an article on Marc Hiebeck's website. http://www.zr1specialist.com/HAT%20Web/articles/Are%20The%20Secondaries%20Working.pdf

Also the plug wires and the coils need to be tested. Just because their new doesn't mean they're good. I believe a plenum pull shall be necessary to fully test and diagnose.




Sent from my iPhone using ZR-1 Net Registry (http://r.tapatalk.com/byo?rid=90383)

[frantinoro]

Alright, I will pull the plenum this week. Can I test all the injectors without removing them, or should I remove them due to the coolant? I will test the secondaries for smooth opening, injectors, as well as coils and plug wires. Anything else?

[Young1]

Marc's site has an article for testing injectors and operation of secondaries. His CD video presentation is great for plenum removal. Put clamps or zip ties on all vacuum and emission hoses. Pull coil tray and pull starter to shine up the solenoid copper contacts while you are in there. Test the electric solenoid vacuum valve. I had it go bad. Read everything on ZR1specialist site. I really think your secondaries are not functioning properly. Are they opening at the same time? Are they smooth and not jerky jerky. Are they opening 100 percent?
Keep in touch. Search and read the stickies here on the forum too.

[dcarroll95]

Ditch the secondaries - they will fail one way or another and if you ditch them no more secondary issues. You'll need a chip from Marc Haibeck to reprogram the car to split injector duty, but then you get a known tune.

While you're doing that test the injectors. Test the coils by measuring resistance between the two plug wires that share a coil. I had one at 30k and the other 3 were 18-20k. The 30k is bad.

Check out the "secondary remove guide" post that I recently commented on. It has instructions that I followed and wasn't too bad. Maybe you'll get lucky like me and find out the heads and plenum were already ported by a previous owner.

[frantinoro]

I JUST ordered a chip, I supposed I could return it. Another hint is my MPG is much lower than what everyone else is registering - maybe that will clue someone towards a potential problem.

[Paul Workman]

I JUST ordered a chip, I supposed I could return it. Another hint is my MPG is much lower than what everyone else is registering - maybe that will clue someone towards a potential problem.

The fuel mpg issue would have me forming a mental list of items to check:

O2 dynamic operation (you'd need access to an OBD-i scanner or equiv. (On two occasions since 2002 I experienced excessive fuel consumption. Both times I had issues with O2 sensors - verified with the scanner.)

I'd want to be sure the resistance linearity of the TB did not have any glitches across its entire rage of operation (throttle position).

dynamic fuel pressure: mid 40s (around 45-50 mhp, as I recall), and 53-55 psi at WOT (pressure gauge taped to the windshield)

Are your fuel injectors OE? If so, they need to be replaced with new alcohol tolerant ones - asap, w/o fail! (I experienced a burnt valve on the same cylinder occupied with an affected (bad) injector.)

After several maintenance items over the past 16 years of Corvette ownership, I can't say enough about the importance of a scanner or the ability to do so (software/laptop) far as diagnosing and troubleshooting these cars. In no time at all, with the help gleaned from the FSM and the ability to scan the computer and sensors, you can become far better able to assess and correct problems as they arise - waaay beyond that which you will find at most car dealerships (or the like)! Just a thought!

OH! And, something else from the "School of Hard Knocks": Just because a part was replaced, having done so is NOT the same as verifying it is working properly. Assuming the new part is working properly is a classic troubleshooting failure!: ya gotta TEST it to verify proper operation. Never assume!!!

[dcarroll95]

What type of scanner can we get that will hook up to a laptop? Just got my ZR1 couple of months ago.

Thanks!

[tnova]

As others with more experience have guided, check all they have listed. I had stumbling secondaries on my '91. Did all the that has been listed and while it improved, didn't totally go away. Even sometimes felt weak on primaries, but mostly under hard acceleration. Was hell getting it through CA smog. Skip two years forward and I found the problem, car had 160,000 miles on it and the catalyst in the converters had collapsed. They sounded like gravel in a tin can. So, hopefully your problem resolved before you get to this possibility. My fix - moved to WA with no smog for '91 and headers with C-6 cats.

[mike100]

As others with more experience have guided, check all they have listed. I had stumbling secondaries on my '91. Did all the that has been listed and while it improved, didn't totally go away. Even sometimes felt weak on primaries, but mostly under hard acceleration. Was hell getting it through CA smog. Skip two years forward and I found the problem, car had 160,000 miles on it and the catalyst in the converters had collapsed. They sounded like gravel in a tin can. So, hopefully your problem resolved before you get to this possibility. My fix - moved to WA with no smog for '91 and headers with C-6 cats.


wow! really?..haha

[tnova]

Mike, Long time since we last talked. Yup, surprised about finding the catalyst collapsed. After all the troubleshooting we did and not getting the stumble/lag resolved, especially when real-time testing with your Tech. I only stumbled on it when shelving the old exhaust manifolds and hearing the rattling around in the cat. Looking back, it was a classic symptom of blocked exhaust.


Recently had a cousin with the same symptoms on his daily driver and he found the catalyst collapsed in the converter. Replaced it and now runs like it should.


In chasing the symptoms you and/or I validated the operation of the secondary vacuum system, the FI drivers, replaced the injectors with FIC injectors, replaced coils, replaced O2 sensors, upgraded the fuel pumps, validated the secondary and FI signals from the ECM, and the prom. Not all for not but a lot of time and money.


Again, thanks for all the help.
Tony - Tnova

[Paul Workman]

As others with more experience have guided, check all they have listed. I had stumbling secondaries on my '91. Did all the that has been listed and while it improved, didn't totally go away. Even sometimes felt weak on primaries, but mostly under hard acceleration. Was hell getting it through CA smog. Skip two years forward and I found the problem, car had 160,000 miles on it and the catalyst in the converters had collapsed. They sounded like gravel in a tin can. So, hopefully your problem resolved before you get to this possibility. My fix - moved to WA with no smog for '91 and headers with C-6 cats.

Ha! Interesting - one for the memory banks (just in case).:cheers:

[frantinoro]

Alright guys, im back. All injectors tested to be 14.7-14.8 ohms, the secondaries freely open with 10 hg pressure, the reservoir holds a vacuum, and so does the solenoid. Vacuum pumps up to 15 hg, and cycles every 15-30 seconds, no obvious vacuum leak. I read online to jump the C17 connector pink wire; but I tried to jump what I thought it was and it just sparked. Any advice on what to try next? All of the coils also gave me 5.5-5.6 ohms when set to the 20K setting.

[frantinoro]

Just tested the solenoid, jumped the C17 wire, and the secondaries are opening smoothly

[frantinoro]

So when I reassembled everything, the right bank of secondaries got caught up a bit, and I noticed that the tab leaving the vaccum thing was bent, bent it straight and it seems to be a lot smoother opening. Resealed the PCV while I was in there, and blocked off all the coolant ports.

Does the injector housing gasket need sealant on it? Torque specs on the Injector housing, and PCV cover? Also, where can I find a shop manual, as I can't find any of this stuff online.
Thanks,
Francesco

[Dynomite]

Does the injector housing gasket need sealant on it? Torque specs on the Injector housing, and PCV cover? Also, where can I find a shop manual, as I can't find any of this stuff online.
Thanks,
Francesco

Go to Post #8 in -Solutions- for bolt torque.
Since you have coolant in Injector Housing I always use a bit of Permatex on both sides of the Injector Housing Gasket.

Since you blocked coolant (at Injector Housing??) you would not have coolant through TB so I do NOT use sealant on Plenum Gasket and do not torque Plenum as much as stated in Post #8 of -Solutions-.

All of this "stuff" is in my Signature......just left click any item.

[frantinoro]

Been a while, but I'm back. Ended up picking a MT2500 snap on scanner, and here are my results, let me know if anything seems out of wack. Car seems to hunt for an idle like crazy sometimes, and has a misfire, which you can hear out of the right exhaust bank at idle.

According to the scanner, the TPS is at 0.44V and should be a couple millivolts higher. Could this cause an issue?

IAC counts at idle is 0, but when revving it it goes to 30 and stays.

It mentioned some starter test for AC voltage leak down, but I don't think I have that issue.

Other than that, everything seemed normal. Going to do a drive and see if I can get anything else to pop up. Also to the people saying cats, I smacked them and heard no rattling, and when I did my clutch it looked pretty normal to me, I'm not sure if you can notice a ruined cat vs a healthy one though.

[Ccmano]

Been a while, but I'm back. Ended up picking a MT2500 snap on scanner, and here are my results, let me know if anything seems out of wack. Car seems to hunt for an idle like crazy sometimes, and has a misfire, which you can hear out of the right exhaust bank at idle.

According to the scanner, the TPS is at 0.44V and should be a couple millivolts higher. Could this cause an issue?

IAC counts at idle is 0, but when revving it it goes to 30 and stays.

It mentioned some starter test for AC voltage leak down, but I don't think I have that issue.

Other than that, everything seemed normal. Going to do a drive and see if I can get anything else to pop up. Also to the people saying cats, I smacked them and heard no rattling, and when I did my clutch it looked pretty normal to me, I'm not sure if you can notice a ruined cat vs a healthy one though.

What mods, if any does the engine have? TPS voltage should be .54volts at rest. That’s one issue. IAC count should be ~10 at idle when fully at operating temperature. This indicates you have an intake vacuum leak somewhere. Start with the TPS and reset to .54v. Test again and see if the IACs change. If not start looking for an intake leak. Keep in mind your intake leak could be the throttle plates themselves, but more likely somewhere else.

Go through this Haibeck article on vacuum leaks before you start.
H
:cheers:

http://www.zr1specialist.com/HAT%20Web/articles/Finding%20and%20Fixing%20Vacuum%20Leaks%20on%20the %20LT5%20Engine.pdf

[frantinoro]

The secondary system was gone over, and had no leaks. I have plastic wire tied every single connection to minimize leaks. I will test it again though. For the main leak area, the IH has been resealed, and the plenum as well. Throttle body was resealed via the Jerry's Gaskets kit. PCV grommet was replaced, and the map sensor definitely isn't leaking. Are there other areas of leakage I should be concerned with?

EDIT: Everywhere I've looked the ZR-1 TPS shouldn't be adjustable. But mine looks like it is. Is it?

[Ccmano]

The TPS sensor should have slotted mounting holes. If not you have the wrong sensor. You simply loosen the mounting screws slightly and rotate the entire sensor slightly to get the right voltage. Should look like this....
H
:cheers:

http://a65.tinypic.com/34ot3yq.jpg

[frantinoro]

TPS set to 0.56V, working a little better but now it still has the hesitation, I'll look into vacuum leaks some more.

[Ccmano]

TPS set to 0.56V, working a little better but now it still has the hesitation, I'll look into vacuum leaks some more.

Cool, what’s the IAC count now?
H
:cheers:

[frantinoro]

IAC count still goes down to zero when warm and idles a little high, I'm just not sure where a leak could be.

[Ccmano]

Is it still hunting at idle?
H

[frantinoro]

Yes it still hunts at idle. It also has moments of a rougher idle, and jumps to smooth but I don't see anything in the data about it.

[Ccmano]

Sounds like you went through everything on Haibecks list. I’ve seen them leak at the injector o-rings, a little carb spray at each injector and see if the idle speed changes would show that. We have also see air leaks at the throttle plates. Was the throttle body around the plates cleaned with carb cleaner recently? If so the DAG sealant may have been removed causing more air to bleed by. If you haven’t already read through what member “Roadster” discovered on that subject. http://www.zr1.net/forum/showthread.php?t=27773&highlight=Throttle+body

In any case you have an air leak somewhere and if it’s hunting rather than just a high idle it’s fairly significant. Along with the hunting the zero IAC count is the telling factor of an air leak.

Will you be at the Socal meet in Fontana at the end of the month? I wouldn’t mind looking at it while I’m down there.
H
:cheers:

[frantinoro]

I'm hoping to have it fixed by then, here's another symptom. When I floor it in full power mode, the car shakes quite a bit, and its MUCH less noticeable in valet mode. I figure if the issues is a vacuum leak at the throttle plate, it wouldn't cause an issue once not at idle.

[Ccmano]

I'm hoping to have it fixed by then, here's another symptom. When I floor it in full power mode, the car shakes quite a bit, and its MUCH less noticeable in valet mode. I figure if the issues is a vacuum leak at the throttle plate, it wouldn't cause an issue once not at idle.

What year is the car? Have the injectors or fuel pumps ever been replaced? That sounds like a bad injector, coil or wire issue.
H

[frantinoro]

Injectors have been replaced, fuel pumps are new and are functioning properly according to the scanner, secondaries are opening, and the coils were ohm tested to be okay. Does it when cold or warm so I didn't think it was a break down issue with the coils.

[Ccmano]

You really have done quite a bit. Ohming the coils is not the best coil test, they can ohm good and still be going bad. Drive the car at low speed in a high gear and accelerate slowly. If it misses likely a coil is bad. I assume wires have been ohmed and plugs replaced too. Have you checked to see if the system has thrown any codes. Also what is the fuel pressure static and at full throttle. We’ve seen the Y and connectors at the fuel pumps go bad and loose pressure. Fuel filters get plugged and fuel pressure regulators go bad.

At the risk of stating the obvious are the vacuum hoses hooked up to both the MAP sensors? Something is going on and likely all related.
H

[frantinoro]

So the system JUST threw a code 55, which it has never done before. Also at the risk of sounding stupid where is the second map sensor?

[frantinoro]

So is there a good way to test the coils or just 4 new? Plugs are new and wires ohmed good.

[Ccmano]

So the system JUST threw a code 55, which it has never done before. Also at the risk of sounding stupid where is the second map sensor?

MAP sensors are at the back of the plenum, likely the one you are aware of, and under the ECM Mount. Code 55 is a “Fuel lean” code which could coincide with either a vacuum leak, fuel supply issue or both.
H

[Ccmano]

So is there a good way to test the coils or just 4 new? Plugs are new and wires ohmed good.

If the coils are original I would replace them, they are almost 30 yrs old.
H

[frantinoro]

Coils were supposedly replaced by the PO and look relatively new.

[frantinoro]

I still probably order new wires and coils to be safe as 4th gear low speed bucks quite a lot

[Ccmano]

Do you have a Factory Shop Manual? Diagnostics for code 55 can be found on pages 6E3-A-78 and 79.
H

[frantinoro]

I do not yet. I'll check eBay or something later tonight and probably order one. In the meantime do you think you could PM me the one page?

[Ccmano]

Here you go...

http://a65.tinypic.com/vzwrgn.jpg
http://a68.tinypic.com/skyj52.jpg

[frantinoro]

Okay, I'll test it later when I am out of school. One thing I did notice is my car would stay in closed loop - I assumed it would go into open loop once warm, no?
edit: i see I had it backwards. I will do this test tomororw! Thank you for the picture.

[Ccmano]

Okay, I'll test it later when I am out of school. One thing I did notice is my car would stay in closed loop - I assumed it would go into open loop once warm, no?

Its the other way round, That’s normal, starts in open loop when cold then transitions to closed loop (operating off the sensors) when hot.
H

[frantinoro]

This may sound weird, but I put some gas in the vette because it was so low, and it's not throwing the code anymore...

[Ccmano]

Fuel level should not be an issue. There something going on with fuel delivery especially given the other symptoms.
H