Supra hesitates

[damone]

hey guys/gals, kinda new to the forums.. I have a 90' Supra turbo.. pretty much stock from top to bottem (upgraded turbo, and intake) Im havin' a problem with it.. well, im ALWAYS havin problems with it, but this one I cant figure out...

It started a couple days ago, while accelerating sometimes it will hesitate real bad.. before I could just feel a slight hesitation in the gas peddle, now the whole car jerks.. And I also noticed that a couple times the tach needle kept jumping around after the hesitation stopped.. it doesnt do it all the time, and it only lasts for a couple minutes or so, then goes away..

The car isnt throwing any codes, fixed a few vacuum leaks, cleaned the TB and ISC.. hasnt helped at all..

Did a search, come up with possible TPS problems??

Anyone else have any ideas of where to start??

this problem is

[Jeeves]

TPS alignment can correct many issues, it's a pain in the ass, but can solve some stuttering and stalling issues. Never quite heard of a TPS causing all out jerking.

My list of things to check:
1) Fuel Filter (depending on mileage)
2) Spark Plugs
3) Plug Wires (I found a taped together #2 plug wire on my own car from the prev. owner)
4) TPS Alignment (I'll post the procedure when I get home, I'm on the road ATM)


On the other hand. What all do you have done? Boost controller? Fuel Control (afc)? What is the upgraded turbo (60-1?) Aftermarket Exhaust? Etc.

[TcmaBoy]

You mentioned that the tach jumps arround after the hesitation stops. Dose the engine rev up and down, or is it just the tach acting crazy while the engine runs normal? I had a problem like what your are describing. My engine would stumble both under hard and eazy acceleration. Then it would catch and go. The tach would go crazy! I couldn't figure it out untill I drove at night. It did the same thing, but this time it wasn't just the engine stumbling and the tach going nuts. All the lights started flickering as well. I poped the hood and started looking. I found one of the ingition wires had grounded out and was droping voltage into the body. The igniter wasn't getting power to the plugs, and all that stray voltage was messing with the tach signal. So check for any loose grounds, or broken wires that could be dropping voltage into the engine block or the body.

[damone]

yeah the 14y/o wiring in the car is gettin prety crappy.. I just changed the plugs about a month ago, along with fuel filter.. new MSD superconductor plug wires about 8000kms ago..

the car would hesitate and jerk, and the tach would reflect this.. But after the jerking had stopped and the car smoothed out and drove normally, I noticed the tach bounced around two or three more times before correcting.. So this leads me to believe I have a short or wiring problem..

Your other question, theres no mods on the car right now except for the MSD wires and a 57-1 turbo upgrade..and an intake.. the exhaust is still factory.. I have a BIC 3" downpipe and elbow that hasnt been installed yet, and im gonna get full 3" piping and possibly magna-flow muffler.. And i Dont want to install my boost controller until I get a better exhaust...

Is it true that the ECU stops getting responce from the TPS at WOT? Cuz I checked last night, and it will still hesitate under wide open throttle and I know that a few sensors stop responding at WOT

[damone]

I noticed that the small harness going to the 3 coil packs is in pretty rough shape.. i'll pull that out and have a look

[toyocamry]

I think ur best bet is to check the spark plugs and spark plug wires. My 92 4 cyl camry had that problem wen i got it....and after my moms mechanic changed those things, it ran much smoother. Hope that helps ur problem

[damone]

well I pulled some of the engine harness out today to get a better look and it was pretty bad.. I had to put all new wire in to the coil pack harness, the CPS connector was chopped up pretty bad, as was the ISC connector.. fixed them all.. drove back into the city, and the car hasnt acted up at all yet, but its still too soon to tell if ive fixed it or not...

i'll keep you posted..
thanx for all the replys!

[Jeeves]

Coil Pack, CPS, and ISC. Those would be a weirddddd cause for your symptoms. Possible, but quite odd.

[damone]

ahh dont say that.. your gonna jinx it..

I woulda thought that if the coil harness was grounding out, than the coil wouldnt fire those two cylinders properly, causing the hesitation and jerking??? im sure the CPS or ISC are not to blame, but I just didnt want to have any future problems with them..

[TcmaBoy]

Originally posted by Jeeves
Coil Pack, CPS, and ISC. Those would be a weirddddd cause for your symptoms. Possible, but quite odd.

Its not the parts but the wires going to the parts. Like I said earlier. With the voltage for the coil packs dropping onto the body there isn't enough power to fire the engine. The tach uses a voltage reference from the clynder firing to determine RPM. If you have stray voltage going through your car the tach will pick it up and give an eratic reading. You should give the car a good once over though. Wires grounding out can damage other electrical components. In my case it fried my ignition coil. I hope your problem is fixed. Nobody likes being in the garage when they can be out on the road.

[damone]

well i took her for another spin today.. no jerking, no tach fluctuating *crosses fingers* maybe I fixed it?

I can still feel a slight hesitation once and a while (probably the plugs or wires) but no more out right jerking..

[wambus]

I am experiencing something similar. I have had a problem that only occured when at that point just between accelleration and decelleration - the car would buck. Recently it would do it a little bit while cruising at a constant speed. Now it does it a lot, but only after the car is warm. I will check these items - I just replaced the cap and rotor, and plan to replace the plugs soon. In my post about this I note that the coolant temp sensor is bad, so I capped off both ends of the hose that is related to it. I have not checked the TPS as of yet.