# Help with 1991 Auto Trans problem!!!



## burchs (Dec 4, 2004)

I have a 1990 240SX automatic. My problem is this. It will not upshift until the engine RPM gets to about 4500 and free-wheels when I let off of the gas. Once in OD, it does not free-wheel, but if I get the RPMs lower than 2700, it downshifts and the issue is there again. I have checked to trans fluid and everything looks good. Has anyone had this problem before? I sure would like to drive it again, but it is too much work when friving in traffic.

Thanks in advance.

Skip
__________________
67 Stang
1990 Nissan 240SX


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## aradapilot (May 29, 2007)

I'm having this problem right now...trying to figure it out...might be electrical? what sensors assist the trans?


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## rbo1577186 (Jan 16, 2005)

Band adustment?


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## rogoman (Dec 16, 2004)

Check the TPS harness connector for oxidized pins. If the TPS is not in the circuit, then the A/T will shift hard and at much higher RPMs.


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## aradapilot (May 29, 2007)

tps looked alright, and threw no codes...
heres a copy of a post i made to anothers suggestion of the rev sensor:

I've been having a problem like this recently...I had the car off the road for a while as my camshaft snapped (yes, snapped in two) and finding another was a pain, and now that I swapped the new one in and went for a drive she wouldnt shift until near redline. It seemed electrical...as the tranny had been fine up until then and a few connectors had to be taken apart to do the timing work, including the tps. When I'm home from work tonight I'll try undoing the rev sensor...hopefully it's that, maybe hurt from sitting not running for a while during a heat wave...you'll hear back from me soon.

And a note, I read this whole thread and it's been immensely helpful - would've taken me forever to test all that by myself. Thanks all! Hopefully this will get linked in a sticky or something as it seems to be a common problem.
Okay...same problem with it unclipped (the top connector with 3 prongs next to the relay box, right?). So, trying to figure out what it is. More details:
shifts 1-2 at redline. shifts 2-3 at about 5500-6000. haven't gotten to 4 yet, as i'd need to go about 80 to redline it in 3rd and I don't want to go far from home to a nice highway or anything until I work this out...
also, when it finally does shift, if i let off the gas the rpms drop down to about 1k even if the engine should be held higher by the trans...not sure whats causing this. I can get back up to a normal range easily and the torque kicks right back in.
note: having gears 1,2, and 3 means all solenoids fire. I tried disconnecting the kickdown switch too...no luck there.
Could this be a problem with the tps? what other inputs are used? It seems like the rev sensor disconnect worked for everyone but me...though my problem sounds identical.


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## aradapilot (May 29, 2007)

It's the TPS. was throwing 2.68V at closed throttle as opposed to the 0.4 expected. Just got a replacement, gonna swap it in a little later, I'm tired as hell.
And driving with the bad tps disconnected was fine. Obviously it shifted based on the charts in the fsm rather than pedal pressure, but otherwise performed beautifully.


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