1990 ZR-1 Hesitation when full Power

[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]

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.

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

[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]

Originally Posted by frantinoro

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]

Originally Posted by 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.

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


http://www.zr1specialist.com/HAT%20W...5%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