I have an '87 TPI 350. Fuel pressure is 47psi. Has new distributor, module, wires, cover, coil. MAF was cleaned. 52mm throttle body. new IAC. original TPS and ECU.

I start the car in the morning, then after running for about 5 minutes it starts this problem. WOT the car will die down then try to pick itself back up but the engine just coughs, backfires and sputters but when at a steady RPM (like holding it at 3000rpm) it runs fine and it idles fine and revs fine from idle to about 1500rpm before it starts to cough.

I checked the top 2 wires on the TPS, and there is no drop or pauses in voltage (however, i have only been able to test it when the car is running fine).

my only gueses are TPS or ECU?

 

here's some more info:

Car has sat for the last 9 years, has new engine and a whole bunch of sensors. car sat with battery connected. 8 injectors have been bench cleaned, but not the cold start injector. Injectors Ohms all read fine. I drove it for 2 days before this problem occurred.
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1 more thing:

when the problem DID occur, I pushed down on the TPS while the throttle body was at idle, and pushing the TPS down caused the problem, made it cough, etc.

 

Have you performed an EGR system function check?

 

woops forgot that too, I don't have an EGR system. I have the block off and hedman hedders

 

Do you have Tuner Pro or an multi meter? Check to see if your TPS voltage is correct and smooth in it's change as you open and close the throttle. Check the electrical connector to it. You shouldn't be able to affect a change on the engine by pushing on your tps. Is it loose? Also since it's been sitting check your fuel filter, replace it if you haven't since you got it running. Take a fuel flow test.

 

I'm sorry I just noticed you checked your tps what was the voltage from idle to WOT?

 

.57v to 3.99v

car has new fuel pump, filter, flushed lines, and gas tank was resealed with POR-15 kit. has AFPR and diaphragm looked fine.

 

ok something new, WHEN the problem occurs the voltage on the TPS (top 2 wires) is all weird, sometimes it stays at .57 and creeps to .66, and other times it will creep to a max of 3.v and drop down to .33

 

Sounds like a bad tps sensor, do you have another to swap it out with??

 

That seems like the place to start, buy a new one and see
what happens

 

3.99 is low and agreeing with the other folks, your tps is bad

 

alright, I ordered 1 tonight

I'll let you all know in about a week, thanks guys.

 

Yes don't forget to let us know how
it works out

 

I highly doubt it's the TPS

when it has the problem, it runs like crap, and still runs like crap when I unplug the TPS.
when it doesn't have the problem, it runs great, when I unplug the TPS it's still running great...

I had the problem the other day, and I pulled over, turned the engine off and sat for 30 seconds, then started it again and it ran fine...

the problem doesn't have a consistent starting time when it acts up, it varies.

 

i had the same problem you need to put the o2 sensor back into the headers. i used to have to warm my car up for about 10-15 minutes to get a good idle and even then id lose voltage at lights etc. i replaced the sensor and now it has no problem going from open loop to closed loop.

 

The sensor is hooked up, but it's located at the collector and are full length headers, so I guess I need a heated O2? How can an O2 sensor cause this problem? So the problem will persist even if I unplug the O2?

 

the computer that runs the tpi needs the o2 sensor to tell it to switch out of open loop or closed loop not sure which comes first. it does this by heating in the manifold and when it gets to a certain temp it tells the ecm to change its fuel/air mixture to normal. the reason it dies at lights is because it is not sending proper signals back to the ecm so the ecm needs to guess what kind of mixture. the result is back timing voltage drops. so id say find someone that might knows info about the wiring harness or hook the o2 sensor back up. mine just needed a new sensor but you need to get it in a spot on the manifold that gets hot enough or get a heated one.... me rambling

 

So the O2 tells the ECM what voltage to send to the TPS?

Why does my TPS voltage fluctuate when the problem occurs?

 

the o2 sensor sends data that it gathers from the exhaust temperature leaving the manifolds to the ecm. the computer calculates and adjusts for the best air fuel mixture based on how hot it gets so since your sensor is down on the long tube headers it cools down too much. giving wrong readings messes up the firing of the spark plugs.im guessing everything is tied together and react accordingly

 

basically i went checked all the stuff everyone else has told you to check i came to the o2 sensor. replacing this sensor fixed all the same problems you are having with the voltage and rpm problems. fixing this sensor kept me from selling her because of all the headaches it caused

 

alright i'll order a new O2 sensor this friday, thanks for the info dude.

and well, this sucks lol I just put the new TPS on tonight and the bottom screw snapped off in the throttle body -with minimal force-, now I gotta drill and tap. The bolts that came with it were too long.

 

Make sure you get a heated o2 sensor since you have headers.

 

yep, not the TPS. I'll a order a heated O2 sensor friday.

and the WOT voltage output is now 3.66v (I had to drill a new hole for the bottom)

 

Heated O2 sensor didn't fix it. The sensor I used was a Walker 250-23005. Do these cars have a limp mode? because that's what it almost seems like it goes into. I'll get a video of it tomorrow.

 

I unplugged the EST and it didn't fix the problem either.

here's a video
http://www.youtube.com/watch?v=vPmFtnxekeU

 

it was the MAF sensor. or more specifically, a MAF sensor that was saturated with coolant and had coolant inside of it haha. I took it apart and dried it out, so far I have had no problems