Fouled plugs ?

[A26B]

Dry soot vs Oily soot on plugs would indicate fuel or spark issue as opposed to oil fouling from guides or rings. 4 & 8 are not paired cylinders so it would require 2 coil or 2 plug wire issues.

No fuel pressure leak-down would indicate the injectors are not at fault mechanically.

Question: is the engine missing? Have you tried a low rpm (12~1500 rpm) pull in 6th gear? Does the engine buck or does it pull smoothly/gradually? Weak spark is usually the culprit if engine acts like it has modified camshafts.

Also of note: You mentioned the ECM being replaced. What is the background on the replacement ECM? Used, reconditioned, new, known to be good by test in another ZR-1?

[onetinsoldier]

The ecm was reman from cardone for a 95 zr1 . As far as the 6th gear pull , you have to be going about 80 mph to even think about shifting to sixth , I believe this car has 2;73 gears or close to it ! My understanding is ,that's what got it to the 200 mph mark , I was told the car was tweaked , I just dont know what was changed . The front wheel pressure sensors were removed because they were causing a vibration around 190 and the handling was loose , so they lowered it by removing the factory shocks and put some orange colored ac delco shocks .

Today I did replace the plugs again with rapid fire #5 gapped at 50 , I didnt have a chance to drive it much , so tomorrow I'll test drive it and check the plugs

[secondchance]

It wasn't 2.73 gear that got the car to 200 mph. I believe it was 3.45 in 5th (ZR-1 gurus, please correct me if I'm wrong). If you have to be doing 80 to use 6th, I suspect you may have issue with secondary system. Wheel pressure sensors being removed because it caused the car to vibrate? Is this what the last owner told you or did you remove sensors because the car vibrated when you drove at 190? Where was the car driven at 190? It would have taken more than some tweaking to get to 190.
I would start with proper diagnosis to see if secondary system is operating properly and check all injectors.
Code 64, sooty plugs, blown cats leads me to suspect injector issue.
Also, if I remember correct, .05 gap was for platinum tip plugs. Rapid fire plugs were available in conventional and platinum tips. if non-platinum tip, I believe .035 gap was what was spec'ed.

[onetinsoldier]

the last owner told me the sensors were causing a vibration in the steering wheel that they didn't like , so by removing the sensors, it removed the cause of the vibration .The previous owner probably had the car at the circle track to test it , being that's what he did for a living . And you are right it would take more than tweaking to get to that speed !

[onetinsoldier]

Ok this is nuts , update I put in another set of spark plugs RF5 gapped at .50, I removed the O2 sensor cleaned it with a compressed air spark plug cleaner , drove about 40 miles . No codes were set and no miss ! I will pull the plugs to see how they look tomorrow . I can't believe these engines are that particular on spark plugs !

[onetinsoldier]

Update : I had cleaned the O2 sensor and changed the plugs to Rapid Fire 5, now there's still some soot at the base of the plug, not on the ceramic or the electrode or the ground strap . But no where near what it was , it had Bosch R6 in it , i tried a inexpensive autolite plug , to check it, then put in the RF plugs . Maybe a hotter plug ? Or new O2 sensors ? Both ?

[onetinsoldier]

Ok , update , Now that I have had some time to work on the car , I changed to a hotter sparkplug RF6 and no more sooty plugs . Now to figure out the vibration between 1st and 4th , and from 5th to 6th gear !