High rpm hesitation - is this detonation?
 

88 TII

This is problem that suddenly started to occur. The car pulls hard as normal until I get to around 5500 to 6000 rpms and then the engine starts to hesitate. It is actually sort of a smooth hesitation (certainly not fuel cut). The only thing I can relate this hesitation to is clutch slipage, because that is kind of what it feels like. But there is no way it could be slipping because I installed all new clutch components 2 years ago (including new pressure plate and flywheel) and I hardly ever let the clutch fly.

So what could be causing this? From searching, I've seen some situations which could be the same, in which grounding problems were suggested. Also vacuum leaks could be a problem or something happening with the turbo.

Any suggestions? thanks

Help please?

well being that it is happening around 5500-6000rpm i would say that is the limit of the power curve on a stock s4 t2. Do you have mods? And it very well could be a fuel cut, because thats what the ecu is doing to not let teh motor rev any higher.

Whats the temperature while this is happening? Sometimes mine will do the same when its muggy or like in the high 80's or 90's. And i do have a fcd. Just my opinion.

No, this is a problem that just started to happen. I know what my car normally feels like when it is pulling hard, and this hesitation is certainly not normal. I have a fcd installed so I know this is not fuel cut, besides when the ECU cuts fuel it is like hitting a brick wall, and this hesitation is nowhere near that drastic. This is also something that occurs no matter what the temperature. I have a feeling that it is something to do with vacuum, maybe at the turbo or another connection, but I'm not certain of anything. Any one know about this problem??

any other suggestions

im no mechanical expert and have no idea if its detonation. but if it was detonation try changin to a higher octane fuel
(providing you arent already using the highest) and see if it goes away

my last t2 has a high rpm hesitation, it sorta skipped over 6500, new plug wires fixed it.

misfires/hesitations can be lots of things, but spark is easy (fc only has plugs and wires)

Check your plugs.... if you've done anything to the car to add fuel in a rudimentary way like a pressure regulator or a set of big secondary injectors, it's quite possible that you just gunked up your plugs with fuel. Some call it "The fouling".

Both dr. ifter and j9fd3s posted very good concerns. Both plugs and gas could be a good reason for the ''cutting out''. But if you feel like this might be a detonation, you might wanna consider laying off the throttle so much. How many times are you running that high of a rpm? Gas is expensive bro..........take it easy.

just get a fcd(fuel cut defender) your probly boosting too high, computer automaticly cuts boost to rear rotor if it too high. did you recently put an intake or exaust on your car?

read the thread before putting your .02 in please!

umm, fuel cut feels like you just slammed into a brick wall.

so it's not that.

if your car still runs, it's not detonation either.
Are you using 91 octane?

Check for boost leaks, loose AFM connection, exhaust leaks before the turbo.

Reset your ECU, this has cleared up issues like this for me before.

Most times, detonation sounds like the Keebler elf just jumped into your engine bay and attacked your motor with a ball peen hammer. Your problem sounds like you are going rich due to what I believe (and others on the thread too) to be bad spark pluts. Once you get around the torque peak of the motor, those old plugs just cant light that mix. Throwing hi-test fuel to it will only serve to exacerbate the prob.


Rat

*edit*

Terrh.. Its an S4 ECU. it doesnt store crap..

I know it's an S4 ECU... maybe it was just that one time in particular, but my car had a misfire and the exhaust note sounded a little funny, I pulled the ground cable and put it back on, and it cleared up and was fine.

my car is giving me the same problems.. instead it doesnt start 2 act gay at that high RPMs.. im cruisin at like 25k and it starts choking and backfiring.. i now realize how stupid i am cuz im going crazy tryin 2 figure out wats wrong with the car and i just remembered that i havent changed my spark plugs for like 2 years lmfao0o0

how much boost are you running and what fuel mods do u have besides the FCD?? also check your TPS, see if when in full throttle the ohms reading is between 4-6K ohms

Hey everyone, this is the original poster. I haven't checked this thread for a while because I wasn't getting any responses, now I see there is a lot. Okay, here is the full story...

This problem first started about three months ago, and I instantly got scared that it was detonation I removed my fuel cut defenser as a precautionary measure. Anyway, I haven't been boosting much since then, however now that the weather is nice and warm I decided to put the fcd back in and see if it would hesitate at all. Surprisingly, it boosted better than ever with no hesitation!! Since then I have been doing some searches and found that bad grounding can result is hesitations due to low voltage through the ignition system, so that is what I think was the problem. Maybe now that it is warmer outside the electrical connections are more efficient, resulting in enough voltage. This makes more and more sense because I have always noticed that my headlights get dimmer at idle and many of my electrical components don't work during the winter time but then work fine in the summer.

...Long story short, I am currently considering rewiring the major electrical connections like the grounds, from what I read this can improve the electrical system greatly.

Any additional comments?

Thanks for the posts

I have the exact same problem in my car but it only really starts at 5000+ in 3rd gear. I know I have a small exhaust leak but would that cause a serious hesitation? I'v heard that at really high rpm's it's usually an electrical problem.

i've been having high boost/high rpm hestiations for quite some time now. not a hard fuel cut hesitation. the first time it happened to me i was running way too much boost and the TMIC got too hot. even though i have more fuel and am running less boost, it still does it sometimes.

Maybe its an electrical problem for you guys as well? I won't know if this is the problem or not until I do the rewiring, and I don't think I'll have the time to do it for a while, plus I've got to figure out the whole process. I hear Landers has a good write up at rotaryresurection.com, I'll check that out.

If couldn't see having an exhaust leak causing hesitation unless it was at the manifolds, after the turbo its just a noise issue.

Mine is actually doing something very similar. I recently made a repair to my TID and connected everything back together. At almost exactly 5500 RPM's my boost literally drops to 0 psi. I think it might have something to do with the hairline crack running down part of the hose that connects my BOV to the intake manifold, but I'll check the grounds along with repairing the hose to see if it corrects the issue.

#1 problem of high rpm performance are plug WIRES, not the plugs themselves... easy way to test is unplug a wire while car is idling and DONT ground it to anything, just grip it in your hand... if u feel any discomfort, the insulation is failing

plug wires are too often overlooked

i have new wires....although, they're the cheapy advance auto brand. but it did it when i had magnecor wires too.

although, my turbo to BOV pipe connector is very hard. maybe it's leaking enough to cause issues.

im getting the same prob as well. its at the 6k mark but only at full boost. like its hitting a fuel cut cause it keeps backfiring on and off like fuel cut. this is a 91 S5 turbo installed in an FB. i was thinking i could be missing the low millage sensor causing the car to cut fuel so i dont "hurt the new engine?" that and my o2 sensor is not plugged in either and i have to look at my temp sensor i think it might be bad. if it is bad i think that could solve the prob