Weird stuttering issue

[TX '90 ZR1]

Originally Posted by 32valvZ

I dunno, but with the 80 plus vehicles that have gone through my hands, I would never drive them hard until mostly or fully warmed up. I suppose Im old school, but and engine, is an engine, is an engine.... regardless of modern computer aided fuel systems making the engine "seem" like its ready to be driven under any circumstances, the engine is still made of metals which need some time to warm up before flogging... Oil needs a chance to warm up as well as coolant.... Like I said, maybe Im just old school, ya, I am... LOL.... but none the less, letting my autos and trucks warm up, I believe is good practice.

Amen to this practice! Any engine should be brought to operating temps before putting a load on it.

[Mikey]

Originally Posted by 32valvZ

I dunno, but with the 80 plus vehicles that have gone through my hands, I would never drive them hard until mostly or fully warmed up. I suppose Im old school, but and engine, is an engine, is an engine.... regardless of modern computer aided fuel systems making the engine "seem" like its ready to be driven under any circumstances, the engine is still made of metals which need some time to warm up before flogging... Oil needs a chance to warm up as well as coolant.... Like I said, maybe Im just old school, ya, I am... LOL.... but none the less, letting my autos and trucks warm up, I believe is good practice.

I?ll put any of my cars up against anyone else for best cared for and maintained. The cold engine rev limiter has nothing to do with ?flogging it? per se. Even in the driveway in neutral at 5% throttle the rev limiter still kicks in at 3400 rpm. The Engine is not loaded.

[32valvZ]

Originally Posted by Mikey

I?ll put any of my cars up against anyone else for best cared for and maintained. The cold engine rev limiter has nothing to do with ?flogging it? per se. Even in the driveway in neutral at 5% throttle the rev limiter still kicks in at 3400 rpm. The Engine is not loaded.

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?

Your post above says you hit the rev limiter on a 38 degree morning... the car wasnt fully warmed up, thats why it cleared up eventually and you couldnt repeat it. Thats not what I would call cared for... JMO though...

Furthermore... Why rev a cold engine to 3400 rpm in the first place? Im not seeing the reasoning for that... Fully warmed, sure... maybe for emissions testing procedure or some kind of troubleshooting. Other than that, I see no reason to rev up an engine ESPECIALLY knowing its a cold engine.

Again, just my opinion....your car, do what you like...

[XfireZ51]

I?m up here in Chicagoland, and whenever I start my motor, I always do a warmup to about 60C before putting it in gear. By the time I leave my development, its usually in the 75C to 80C water temp. Still don?t beat on it till oil temp gets a bit higher.

[Pete]

Just because full power is always active and secondaries removed does not mean they are working.
Just because you dont have CEL does not mean you have no codes.
Check codes n get back.
Shuttering at 3500 sounds like secondary is shutting down.

Pete

[Mikey]

Guys I really don?t care if you believe me or not but anyone who knows me knows that my cars are not abused beyond what the engineers who designed them for intended. Maybe you will be less confused if you understand that I have 4.10 gears in the rear so hitting 3500 RPM in first gear is not moving that fast or trying very hard.

Pete, thanks for your reply that is interesting and I did not know that. I will investigate if I have time over the holidays. Cheers!

[32valvesftw]

Change your spark plugs and see what happens. It's easy and cheap. I had a little stumble on mine a couple of years ago and it cleared up with new plugs.

[Pete]

Originally Posted by 32valvesftw

Change your spark plugs and see what happens. It's easy and cheap. I had a little stumble on mine a couple of years ago and it cleared up with new plugs.

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

[rkreigh]

Hey Pete thanks!!


I tested and dynoed some of the fancy plugs and sure enough these did just as well if not better. Pete love to hear more about your engine and suspension tuning tricks on the Z.


You've squeezed impressive performance out of the stock block and tested more stuff than anyone I know.


Thanks!@!

[Pete]

Thank you Ron
I'll be testing new custom induction/TB set up hoping to squeeze a few more out of my 441
Will keep you guys posted.

Pete

Originally Posted by rkreigh

Hey Pete thanks!!


I tested and dynoed some of the fancy plugs and sure enough these did just as well if not better. Pete love to hear more about your engine and suspension tuning tricks on the Z.


You've squeezed impressive performance out of the stock block and tested more stuff than anyone I know.


Thanks!@!