1991 ZR1 engine knocking on idle
 

Hi, after almost 3 months shipping in a container the engine started knocking on idle. I assume it's misfire so clutch cnocking is just a result of it. About my car:
-43k miles
-Haibeck chip
-FIC injectors, coils, plug wires and plugs replaced in 2011
-injector resistance on cold engine 15.2 +/-0.2 ohm.
-replaced clutch
-fuel pressure before start goes to about 50 psi (I wasn't able to check FP on idle because I bought the cheapest tester. I'll try to fix it and check FP on a working engine)

Now my plan is to change plugs, because that's the only thing I can do by myself before going to service. Maybe O2 sensor? I also purchased LiquiMoly Injector Reiniger. I read that could solve the knocking problem.

https://youtu.be/MhHxa_B8J8w idle sound
https://youtube.com/shorts/1snaGeQkXD4?feature=share

I will appreciate all your inputs.

Re: 1991 ZR1 engine knocking on idle
 

That doesn't really sound like misfire to me, but hard to tell with audio quality. Sounds more like very excessive valvetrain noise. So maybe misfire, but not in the sense of spark problem, more like valve problem possibly.

how is the oil pressure?

Re: 1991 ZR1 engine knocking on idle
 

Get an automotive stethoscope to isolate the noise.


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Re: 1991 ZR1 engine knocking on idle
 

I could tell the car had a miss the instant it started,that knock is a combination of flywheel,cam chains.

Re: 1991 ZR1 engine knocking on idle
 

Perform a thorough Italian Tune Up. That will do it.

Re: 1991 ZR1 engine knocking on idle
 

Keep in mind one of the O2 sensors is a real hassle to change. The knock is caused by injectors or spark.

Re: 1991 ZR1 engine knocking on idle
 

It's too bad the mic was not down lower closer to the exhaust and also closer to the engine. That is...two different recordings.

I've played that footage a couple of times. Once with the volume as loud as my computer could go. It's really hard to tell but I think I could hear a "dead miss" in the exhaust in sync with that bad rattle from the engine.

Without better audio or a stethoscope session, I'll make a wild-assed guess that a valve lifter(s) have failed. The engine has a stuck, bent or broken valve.

It would be great to find out of the rattle is coming from the engine or the clutch housing and if from the engine, which bank.

Re: 1991 ZR1 engine knocking on idle
 

Here is an update. I changed the plugs and #8 plug seemed to be different than others (wet). New plugs didn't change anything. Then I checked spark on each cylinder using spark gap tool. No spark on #8 cylinder but nice long blue spark on #5. Also pulling #8 wire made no difference on idle roughness unlike pulling the others.
Attachment 17987
I checked resistance on wires 5/8 1/6 2/3 4/7 and all measured 8.1-8.3 kOhm so there is an electrical connection from #8 plug to 5/8 coil. I'm aware of a high voltage there so my measure doesn't eliminate connection as a posiible cause.

Also I read a different opinions whether it's possible or not to have no spark on only one cylinder caused by the coil in a wasted spark system. Any experience with that?

What brand poduced yellow coils for ZR1?

Now I'm preparing for plenum pull, already got new coils and wires prepared and new gaskets from Jerry are on the way to Poland.

Re: 1991 ZR1 engine knocking on idle
 

The dual-mass flywheel will sound like an engine knock if the engine is not running correctly.

Re: 1991 ZR1 engine knocking on idle
 

Yes, it can happen. Replacing the coil will correct the miss.

Accel brand