1991 ZR1 engine knocking on idle

[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]

Originally Posted by 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.

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?
IMG_20220708_213647.jpg
Should I be concerned with the amount of oil on the case ventilation cover?
IMG_20220708_224601.jpg
Why I don't have a temperature senson on my throttle body extension? Is it a common mod?
IMG_20220708_161914.jpg

[WARP TEN]

Originally Posted by 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?
Attachment 18139
Should I be concerned with the amount of oil on the case ventilation cover?
Attachment 18140
Why I don't have a temperature senson on my throttle body extension? Is it a common mod?
Attachment 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]

Originally Posted by 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?
Attachment 18139
Should I be concerned with the amount of oil on the case ventilation cover?
Attachment 18140
Why I don't have a temperature senson on my throttle body extension? Is it a common mod?
Attachment 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?