coolwind57 Posted 23 hours ago Share Posted 23 hours ago I've had limited time to look into this so far but I'd like to go ahead and toss this at you guys to see if I can quickly remedy this with your experience and knowledge for the next time I can afford a few minutes. My 89 AW-4 Automatic (paired with 4.0L) began shifting erratically and within a few minutes stopped messing around and refused to budge past 1st gear. I had to drive 3 miles back home in 1st. This occurred only 2-3 minutes into the drive. I parked and didn't look into it for a few weeks. Today, I got into it and ran it. Same thing, worked great for a couple minutes and began shifting funny--like it was searching or something, then it lost it's ability to leave 1st gear. I got home and reset the transmission shift cable (using that little button reset method found near the throttle body). I checked the fuse that likely goes to the TCU--yellow wires, in-line 10amp fuse at passenger foot well. The fuse and wiring looked great, btw. Next thing I did was pull the fuse and attempted to drive. Without fuse, it reeeeaaaalllly didn't want to move at 1st gear and the truck crept along. I replaced the fuse and it moved via 1st gear normally. What's the next check? Maybe TPS? Should I swap in a new one? Any other troubleshooting you can think of to narrow this down? Sound like a bad TCU maybe? It's my understanding that the AW-4 is overall pretty hearty. Appreciate your thoughts. Link to comment Share on other sites More sharing options...
coolwind57 Posted 2 hours ago Author Share Posted 2 hours ago I've got a Standard Motor Products TH67 (not the inferior TH67T) TPS on order that I found at a great price, so that's what I'll replace next to see if that'll take care of the problem. Maybe I'll find some time in a few days to go test the old one. If this is not the issue, then at least I'll have a backup TPS on hand for the future. just an update for those interested in following this issue with me. Link to comment Share on other sites More sharing options...
llhat Posted 1 hour ago Share Posted 1 hour ago (edited) 22 hours ago, coolwind57 said: Next thing I did was pull the fuse and attempted to drive. Without fuse, it reeeeaaaalllly didn't want to move at 1st gear and the truck crept along. I replaced the fuse and it moved via 1st gear normally. What's the next check? Maybe TPS? Should I swap in a new one? Any other troubleshooting you can think of to narrow this down? Sound like a bad TCU maybe? It's my understanding that the AW-4 is overall pretty hearty. Appreciate your thoughts. with the fuse pulled you 'should' have been able to manually shift the transmission to 1, then move toward D (it skips 2nd and goes to 3rd) you will not have overdrive or TC lockup... I drove mine around for a good while manually shifting [it would try to start off in 3rd gear, then would 'go' when i moved the lever to 1] According to a recent thread just down the way, read it even though the title of the thread seems not related... The TPS may be a decent trial, but you 'can' test the output ( I think analog meter is preferred to see sweep and any dropoffs) otherwise look at an older thread i started..(it is about 7 pages back !) it had a LOT of tips from Ohm and tests to wiring.... Ultimately 'my' issue was the TCU, but there were a LOT of red herrings along the way... including the NSS... I do wish for you expedient repairs! Edited 1 hour ago by llhat post2 Link to comment Share on other sites More sharing options...
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