91 Prizm misfire post transmission replacement

geo
misfire

#1

I’ve got a 91 prizm where on a recent roadtrip the transmission went out on the freeway. While driving 75mph, i heard a quick ping sound, then a quick wheel skip followed by the sound of my transmission turning itself into gravel. We had just enough time to get off to the side, but i knew it was done.

I live in San Francisco and don’t feel like getting a new car only to get it covered in dings from all the bad drivers around here. So naturally i replaced the transmission in my 22 year old car. yikes. It needs to be stated at this point that the car has run flawlessly it’s entire lifetime and I’m the original owner - had no reason to expect otherwise after replacing the transmission.

The shop that changed it was a large shop, AAA recommended and Owner-operated. They told me the transmission was from a car from Japan where transmission replacement is standard. (I did not know this).

Now however, the car has a misfire. No perceivable misfire for the first two minutes she’s running, but then constantly misfiring every couple seconds. At stop lights, you can feel the car almost want to stop, but then step on the gas and runs ok, but can still feel the misfire until she gets up to speed. The car runs just a smidge rougher so we believe it’s still misfires while at speed, just not noticeable.

  • Timing belt only has 10,000 miles.
  • Timing is dead on.
  • Wires are good, just changed the distributor, coil and plugs. As i understand it, the throttle position sensor is integral to the distributor, so that’s new as well.
  • Fuel pressure is right on.
  • No warning lights on dash.

At this point, I can’t keep throwing money at her. The transmission was 5-6 months of a car payment for a new car. I’m hoping someone can shed some light on this matter so we can keep her.

Would there be a reason that the car would have a misfire after getting the transmission replaced?

Any help/suggestion would be appreciated to discuss with my mechanic.


#2

No, there’s no reason a misfire should show up, even if the new xmission was bad. And the new xmission works ok, right? Pulling the xmission involves undoing, removing a lot of stuff, some of which is done simply to make room and has nothing to do with the xmission, so something connected to the engine probably didn’t get hooked back up correctly.

hmm … is the check engine light on? Your car is OBDI, so there aren’t many codes, but a lot of the free places only can read OBDII. That’s probably where I’d start, reading the stored diagnostic codes. This is something you can do yourself without special tools required, but you need to find a manual for the procedure. The codes are blinked out on the dashboard.

"Could be any of a dozen things. I guess the order I’d go about it is this, after doing the DTC test above …

  • Careful visual that all vacuum lines are connected correctly (use under-hood diagram)
  • Careful visual that all electrical connectors are connected correctly and to the right gadgets.
  • General check for vacuum leaks
  • EGR test
  • O2 Sensor is connected and seems to be working
  • No leaks in Exhaust system

The throttle position sensor … no, I don’t think it is part of the distributor …
About the distributor … why did you change it? B/c of this problem? Or did the problem happen after you changed it? If so, that would be the prime suspect. I think the coil and crank angle sensor is in the distributor on your car.

Anyway, that’s where I’d start if it were my car. It may take some hours of diagnosing this, but I expect the problem will turn out to be a simple error of some kind during the buttoning up after xmission replacement. Did you consider taking the car back to the xmssion shop and asking them to double check?

Edit …

If you have access to an identical car, and want to avoid calling in a pro, that would be a good way to compare the vacuum lines and the electrical connectors were hooked up correctly.