Need help - 3.6 strange problems persists??

[ecm911]

Its a 93 3.6 with several mods:

But Engine stock; Fuel cell,
B&B headers, w/ Cyntex custom chip/

Problem - when engine is hot and under load it appears as thoughth it hits the rev limiter about 5K rpm. Gets worse if you continue to drive - starts @ 4K . Also backfires on shift and decel.
Car runs great at idle and normal driving, when pushed ( on track) the problem becomes evident. Note: Problem cannot be replicated on dyno- tried for two hours.


We are at our wits end - what has been done todate:

NO ERROR CODES - at anytime. Check by Porsche mech
Replaced complete Brain - with stock chip,
New Distributor,
New Barndoor,
replaced o2 sensor,
ran w/o o2 sensor,
new spark plugs,
new fuel pump,
adjusted timing sensor,
checked cylinder head temp sensor,
new coils,
check fuel cell for proper venting,
check by pro for vacuum leaks.
Several P-car mech have taken at shot - to no avail.

All have not effect on problem - HELP?ht is to replace the knock sensor and/or fuel cell issues?

Any advice is GREATLY Appreciated.

Our latest thought - replace knock sensors and fuel cell issues. But we are getting to the end of our rope.!!!!

[ecm911]

Sorry for the typos.

Also the fuel filter was changed.
Also car has light weight flywheel.

TIA,

Earl

[Jeff Alton]

There has been some problems reported lately about he Cyntex chip, try a search and you should find plenty of answers!

Jeff

[ischmitz]

Have you checked the fuel pressure?

[Porsche Doc]

Check for a broken outer valve spring.
If none of the above.

[Mike Feinstein]

Stop spending money! It's the chip. I have the same problem. Cyntex is aware of it and Dr. Timmins is aware of it. Supposedly they're working on a fix, but that's been the story for about 6 months now.

It's intermittent and there's no way to pinpoint the cause. Mine does it pretty consistently at 6k rpms. Suggest you contact Cyntex or the distributor who supplied the chip. If you do so, please let us know the results. I've not had much luck getting definitive answers.

[ischmitz]

Mike, you are referring to a 993 VRAM chip that Cyntex has problems with. Earls motor is a 964. That's a completely different animal. Furthermore, he stated that he swapped the stock chip back in and that didn't fix it.

I think the valve spring could be a good guess once fuel starvation has been ruled out.

[Tinker]

He mentions that he replaced the brain and tried a stock chip.

Have you tried swapping the ignition control modules? I have heard when one goes bad it can cause all sorts of strange problems.

Or how about a voltage or alternator problem?

Tinker

[Mike Feinstein]

Originally posted by ischmitz
Mike, you are referring to a 993 VRAM chip that Cyntex has problems with. Earls motor is a 964. That's a completely different animal. Furthermore, he stated that he swapped the stock chip back in and that didn't fix it.

Ingo, you're right....I saw the symptoms and the Cyntex chip and drew a hasty conclusion. If he substituted a stock chip and the problem persists, guess it makes sense to look elsewhere.

[ecm911]

Thanks all for the replies.

Its not the chip, we swapped out the entire Brain with a stock chip.

New fuel pump and filter and pressure was checked by mech.

Will check out the outer valve spring- would this be an intermittent problem? I believe it its heat related in some way. It can be driven hard for about 20-25 minutes with no problem.

What about the fuel cell? Any problems with these?

Thanks again!!!!!!

Earl

[johnsjmc]

It sounds like fuel moving away from the pickup in the tank to me. The diff. between dyno and track is the actual foreward and back movement of the vehicle. Backfire or popping suggests mixture changes as well.Can you rig a pressure guage to moniter the fuel press when running on the track? I have seen a broken valve spring but it would cause a missfire above a certain RPM (valve floating)regardless of temp.

[ecm911]

Thanks that is an idea - to rig a fuel gauge for track! may give it try.

Thanks for the input on the valve spring, also.

Does the fact that it backfire indictae mixture is too rich or too lean? Or could it be ether?


Thanks
Earl

[ecm911]

Although we tested the cyl head temp sensor, many have posted problems with this. Any comments on this? How difficult to replace?

Anyone have any comments on the knock sensor?

Thanks,

[Speedster94]

head temp sensor , than the car would start very bad when Cold and idle poor . I guess something with the Fuel supply , to monitor it while on the track is a good idea .
Harald

[rdane]

Sounds a little like my '95 when I am bingo fuel in the cell at the track.

[ecm911]

Thanks, Going to pull the fuel cell!

For the record, the tank was checked for gas !