1991 ZR1 engine knocking on idle

[evski]

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.

[Mikey]

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?

[lfalzarano]

Get an automotive stethoscope to isolate the noise.


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[Z51JEFF]

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

[Young1]

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

[Z51JEFF]

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

[Hib Halverson]

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.

[evski]

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.
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.

[RHanselman]

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

[A26B]

Here is an update................................

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

What brand poduced yellow coils for ZR1?
Accel brand

[XfireZ51]

I had a spark knock issue which was at least partially caused by ignition coils that presented cracked housings. You can see carbon tracking on the coil surface.
Since you are going to the trouble of a plenum pull, I would also recommend having the injectors flow tested and rebalance the fuel delivery by matching up the injectors properly. You?ll be pleasantly surprised at how much smoother the engine runs.

[WARP TEN]

I had a spark knock issue which was at least partially caused by ignition coils that presented cracked housings. You can see carbon tracking on the coil surface.
Since you are going to the trouble of a plenum pull, I would also recommend having the injectors flow tested and rebalance the fuel delivery by matching up the injectors properly. You?ll be pleasantly surprised at how much smoother the engine runs.

I'll toss out a thought from a long, long, long time ago. Back in the late '60s or early '70s, I had an intermittent miss on my '68 HEMI Roadrunner that I could not diagnose. Late one afternoon, in a fairly dark place, I had the hood up and the engine running. Jiggled the plug wires a bit and saw lots of arcing from the wires to the engine block when they got close to it. Could not see the arcing in bright daylight. OEM wires about 3 years old. Replaced them and everything was fine. I see you replaced your plug wires about a decade ago; maybe a possible culprit by now? --Bob

[XfireZ51]

Did that one also Bob on my 72 Coupe.

[evski]

I pulled the plenum and have few more questions.
What could be that black powder that came out from the vacuum line on the passenger side?
18139
Should I be concerned with the amount of oil on the case ventilation cover?
18140
Why I don't have a temperature senson on my throttle body extension? Is it a common mod?
18141

[WARP TEN]

I pulled the plenum and have few more questions.
What could be that black powder that came out from the vacuum line on the passenger side?
18139
Should I be concerned with the amount of oil on the case ventilation cover?
18140
Why I don't have a temperature senson on my throttle body extension? Is it a common mod?
18141

Boy, the black powder looks like coal from a Lionel train set! No idea what it is, but others likely will. Also not sure about oil but as I recall not uncommon. The temp sensor is commonly moved from the throttle body (which gets hot) to lower down in the air stream. I did that on both my Zs (mounted them in the air cleaner housing) and I think Marc locates them down in the grille opening. As noted, others more currently versed in the ZR-1s will undoubtedly have better ideas. --Bob

[Z51JEFF]

I pulled the plenum and have few more questions.
What could be that black powder that came out from the vacuum line on the passenger side?
18139
Should I be concerned with the amount of oil on the case ventilation cover?
18140
Why I don't have a temperature senson on my throttle body extension? Is it a common mod?
18141

Might be pellets from the charcoal canister.

[Young1]

Yes charcoal pellets from the charcoal evap canister behind the RR tire. The whole line will have to be blown out, the canister replaced, the vaccuum actuator at the canister replaced, and the under plenum solenoid replaced. The canister is ruined by gas getting to it when filling the gas tank to the brim. I have done it all on Quasar.

[evski]

Thank you guys for all your inputs. I just assembled the engine after replacing the coils and wires. Now it's finally running smooth:). I also blocked TB coolant by the way.
What about the charcoal in the vacuum line, I disconnected the vacuum line behind front right wheel, opened the purge solenoid by grounding the ECM pin and sucked all the charcoal from under the plenum. Then blocked the vacuum line, and left the charcoal canister side of the line open. This is temporary solution for the time I get a new charcoal canister. Can anything bad happen with that solution except of fuel smell?