1990 300zx NA Automatic Transmission problems

[TerryPilling]

Just recently purchased the Z. It has been sitting for 3 years and previous owner said it ran fine when parked? Well I hauled it home, replaced blown main fuse, new spark plugs, bad fuel injector, and got it running.

Here is my problem-On my maiden voyage the transmission was slipping and shifting hard at high rpm's until I drove the car around the neighborhood for a little while. The slipping stopped, but the hard/high shifting was still happening. I read a post and adjusted the TPS to .45 ohms (was at .73) and it was a lot better at shifting, except starting off cold it still slipped up to 3~4k rpm before grabbing until warmed up-so I babied it for several blocks. So I thought a good change of the fluid & filter would help. Replaced with 4 qrts and no gears, added a quart and had gears. Took a short drive and was still experiencing the slipping when first driving until it warmed up again. So thinking it might still need a little fluid I added another quart (6 quarts total), couldn't really tell by the clear color if I was putting in too much and all the forums I found stated the vehicle holds about 7.3 quarts?

Now the poor girl didn't want to move at all really, so I assumed it was too much fluid. Sucked out the 1 quart and now it is like stuck in forward gear (PRND21) no matter where I position the selector. It still will only start in Park or Neutral, but it is in gear, as I cannot rev the engine more than a few thousand without feeling the transmission engaging. The vehicle does not want to move forward though until I get it up to 4k or more, and when I say move- it is very slight movement.

Tried to get the TCU to give me a diagnostic report, but the procedure I followed did not return any results (no flashes). The transmission light does come on at start up, and goes out after 2 seconds like the procedure stated it should.


The ECU comes back 55 (no codes) when I ran the diagnostics for it.

I am thinking a bad TCU or stuck solenoids or ????

Any advice would be greatly appreciated. The car has 145,000 miles and the transmission pan had a little sludge and very minimum amount of any metal fines/particles in it when I changed the fluid. The filter looked really clean also.

Terry

[Ace2cool]

I read a post and adjusted the TPS to .45 ohms

4.5V with the key in "run." Not 4.5 ohms.

Sounds like the TCU is dead, if you didn't get any diagnostics. Either that or a sensor is busted. Have you physically checked the linkage?

[TerryPilling]

Sorry I put ohms, meant volts. Physically checked the transmission linkage, No. I was the one who replaced the fluid and filter, and I did not touch the linkage-but I can take a peek at it. Also the car will not start in reverse or drive, so it appears the inhibitor switch is reading correctly. The rpms change pitch slightly when going though the gear selector, just slightly and it seems like neutral is my drive gear, but it won't drive....

I was just reading the manual on how to electrically troubleshoot the TCU, so I will give that a try tomorrow. I was trying to figure out the specific function of the solenoids to see if one stands out as the culprit, but not much luck with that yet. Also searching for a good site to purchase new solenoids?

Thanks for the reply.... I am all ears at this point, never encountered a problem like this??? Way too many damn electrical solenoids I tell ya...

[Ace2cool]

Yeah, that's the best option you have at this point. Unless there's something wrong with the linkage keeping it from sensing gear shift position, or if there's a problem with the OD switch or something like that.

[TerryPilling]

well didn't get to it tonight, so no new information. The overdrive switch does go on and off as i should and when I was able to drive it, it worked correctly. Again thanks for the encouragement and I will let folks know what I figure out. Hope I can figure something out an it doesn't cost me an arm/leg... Wife not real pleased at the moment on my recent purchase.

[Ace2cool]

The good news is, you can find a used auto trans for cheap, which would probably be easier to replace, as long as you're sure it's not a dead TCU.