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%20W...%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.




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[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]

Originally Posted by 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.

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]

Originally Posted by 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.

wow! really?..haha