Weird stuttering issue

[Mikey]

Originally Posted by Pete

Try this.
And do not over gap plugs.
They're some expensive spark plugs that our cars do not like.
Try some cheap AC Delco #41-602 $20 gap at .035.

Pete

Good advice. I only use copper plugs, none of those fancy platinum or iridium types which foul out easy if the coating on the tip comes off. Plus copper is a better conductor anyway. Just have to change them out every 10,000 miles on high performance motors. I will definitely do the plugs now. Not sure why I didn't pull them yet and inspect. I guess moving last year and losing my shop has really thrown off my routine!

[XfireZ51]

Originally Posted by Mikey

Situation:
Bought a '91 368 Corey Henderson built Z with 25K miles a few months ago. Drove it home from WI to FL. Behaved the whole way.
Once in FL I had opportunity to do a WOT run to 7100 rpm in 2nd gear. It hard stumbled (coughed) once for a split second around 3200rpm but otherwise pulled strong. Repeatable event.
Moved from FL to TN drove the car up and behaved all the way.
This morning it was 38 degrees. Leaving neighborhood in 1st gear 20-30% throttle the engine exhibited a 2hz stutter as if I was on/off throttle in the 3000-3500 rpm range. About 6 or 7 "coughs" in a row. Cleared up above 3500 rpm. Was able to repeat it immediately after but no more. Car seemed fine afterwards except for the single cough/shudder that is fairly repeatable as described above.
Seems only to do it in 1st or 2nd. Not 3rd or 4th.

I've put 3,000 miles on it with no other issues.

Thoughts?

Does this happen when easing into the throttle at that point or with a more rapidly increased amount of throttle(ie jump on it)? Is the issue worse with colder ambient temps? Where is the MAT sensor located?
3000rpm w ~ 20% TPS is where ECM goes into PE mode. I had a similar issue a couple of years ago. Crossing into 3000rpm it would seem to breakup a bit then go on. It would act like a miss.

[Mikey]

Update:
Had read a story some months back about early LT5 engine failures and the discovery of a female at the plant who cold started every ZR-1 with her foot on the floor. The article didn't say anything about a cold engine rev limiter but I suspected maybe the ecu had one implemented after engineering witnessed this crazy abuse.

I had lunch with the assistant chief engineer for the C8 LT2 engine in April (I grew up with him, friends since 5yo) and neither he or his boss knew for sure about possible 2nd rev limiter back in that era. And of course my car was too warm still after lunch to replicate the cold performance symptoms.

Watch this video. At 13:30 he discusses the story I had read about and confirms indeed a second rev limiter was implemented!

https://www.youtube.com/watch?v=6Vs2tdR-9C8&t=810s

[HAWAIIZR-1]

Some believe you will have engine failure if you do not use AMSOIL!


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[XfireZ51]

I don?t think there is any limiter based on coolant C vs rpm in the calibration other than fuel and SA cutoff. May be that?s what he is referring to. I believe there are limiters based on oil temps but that would be for use of secondaries. Need to revisit the calibration Mask IDs to determine for certain.