Mechanics

TRANSMISSION SHIFTING EARLY/LATE (ALSO****** WHEN SWICHING LATE)

1990 Pontiac Firebird • 186,000 miles

Ok I have a very odd problem. This happends everyday. Its a automatic transmission.

Basically, when I start my 90 firebird 3.1L, everything is great. When I go and drive around weather its in town or around town, it doesnt switch gears until around 4000 RPM which is waaay too late cause its eating up gas likes its candy. It also****** hard ****** whole car forward) when it switches in the high rpm (this is first gear going to second gear). It does this for all gears. Usualy the longer im in a high rpm (say I steady it at 3000 RPM for a good minute of driving in say 3rd or 4th gear) then it finally changes after a while. It will also change a lot sooner if I hit the gas and floor it to 4000rpm then it finally changes.

That all happens everyday while on short drives or drives where I stop alot (stop lights/signs) However if I go on a long drive say to the next town over or anything like 10 minutes of driving, then it switches too soon! So for example lets say im driving it in 4th or 5th gear going 65 or 70mph for 5 minutes straight. When I get to the stop light and I stop and wait for green light, I go and it switches at say 2000 RPM to 2500 RPM for all the gears! Now im hitting the gas and it speeds up a little but sounds like im drowning the engine with gas since its pedal to the medal and its not kicking down a gear to say pass somebody up or just go faster. I have to manually shift it down a gear to do this.

The early shifting I would prefer since I can easily manually goto gear 1-3 and then into overdrive cause at least this way I can save gas when im in town which is where im at the majority of every freak-in day!

So is it a bad transmission? A bad sensor somewhere? I have been driving it like this for a year now due to financial difficulties
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Jazzman170
November 3, 2011.




It sounds like an electrical problem. Has the check engine light ever come on? Have you ever checked it for codes? Is the trans fluid clean, full and unburnt?

Check engine light came on once when a fuel injector went out and the whole engine ran like crap cause only 3 of the 6 injectors were firing. That was the only time it ever popped on and once I fixed that, its been a month or so and it hasnt ever popped on since.

I havent checked for any codes yet. A check engine light would come on if it had any codes wouldnt it?

The fluid is perfectly clean. In fact I just put in some kinda tranny non stick fluid that helps it with this kinda stuff sapposedly lol. Made no difference.

Tiny
Jazzman170
Nov 3, 2011.
The light would come on if there is a code. Do me a favor. It has been a while since I worked on a 90. Check to see if there is a vacuum modulator mounted to the side of the transmission. It will be round and have a vacuum hose going to it. They were usually on the passanger side.

Unfortunately its pitch black outside right now and the car is so low to the ground that a toothpick will barely fit haha. Your thinking its the speed sensor? I was thinking the same due to a symptom of a bad or failing speed sensor is irregulor shifting or hard shifting and another symptom is speedometer stops working. My speedometer works fine but if its the shifting part that went bad on that sensor is that possible?

Also I checked autozone and the only sensor they have for a 90 firebird is a "Speed Sensor". I tried "Transmission Sensor" and Speed sensor is only thing that pops up so im guessing thats the same thing? Which case that would mean yes my tranny does have one of those mounted by it or into it.

Tiny
Jazzman170
Nov 3, 2011.
I asked my friend (Mechanic) about it and he said its bolted in to the tail shaft (whatever that is haha)

Tiny
Jazzman170
Nov 3, 2011.
The tail shaft is the part of the transmissions closest to the driveshaft (rear of the trans). The module that I refered to will be in front of that. As far as a speed sensor, yes it could cause a shifting issue. But, it usually affects the speedo too.

Hmmm so theres a good chance that its probably NOT the speed sensor. Im hoping to get a hold of a 91 camaro in 2 weeks for 500 bucks and it has a 5 speed manual tranny that I would love to put in my firebird. Hopefully in 2 weeks ill be able to do so and this will solve all those issues since I CHOOSE when to shift lol.

Tiny
Jazzman170
Nov 3, 2011.
That is my first choice. Transmission today have become way over engineered. There are too many things to go wrong with them.

Just to add, I looked up potential problems that can cause this issue and there is a huge list. Gov assembly sticking, TV cable broken or not adjusted. And the list goes on

Haha ya ill go with putting in a manual! Thanks for your time : P
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Tiny
Jazzman170
Nov 3, 2011.
Let me know what you find.


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