90 FWD, 4EAT suddenly not going up past 2nd gear

[Skube]

163k on this car, which I have been told should go twice this far. Tranny was recently swapped for a lesser mileage, 94 4EAT. All was going fine for a few months, but yesterday on the way home from a 20 mile trip it wouldn't go into 4th, and the speedometer was no longer working.

I let it rest an hour then went back out and it wouldn't go up to 3rd! Starts in 1st and goes to 2nd just fine. Won't budge from there. Fluid level is fine.

I think it's electrical since there was no indication of slipping, or odd noises, or anything like that. Also, the guy that put this tranny in had a similar problem at first, and claimed the 'manual' button caused it. He messed with wires, but I couldn't duplicate the problem by pressing the manual button or not. It seemed to work the way it should. Therefore, I think this problem showed up for him and went away 'magically' or accidentally.

Also, I ran the codes on the tranny and it comes up normal. I get the flashing 'Power' light after going through the shift/manual/on/off, press the accelerator, sequence as the manual shows. The Power light flashes 1/4 second continuously.

I tested the inhibitor switch and it is working properly. The TPS is good, I can't see the speed sensor to check it's connections. Any idea where to look for this thing? Could it be causing the problem?

I fiddled with the AT control unit, pulled the wires and opened the box looking for obvious problems but saw none.

All I can think to do is check connectors for good electrical contact, (if I can find the connectors!)

Prior to the problem the tranny was shifting hard from 2nd to 3rd, and not slipping into 4th reliably. Also, at highway speeds when I romped it, it shifted back and forth rapidly from 4 to 3 to 4 a couple times, (sticky valves). I wanted to get it flushed but no shop would do it for me. A couple mechanics told me about Lucas so I put in 24 ounces of the stuff after taking out 24 ounces of the old fluid. It really helped a lot! Smoothed out the 2 to 3 shift and into 4th the way it should. Downshifting for passing was suddenly smooth as silk. Very nice! That was a couple weeks ago. I took a 300 mile trip on it since then and still had it stick and not go up to 4 a couple times. When I stopped and started up again, it went up to 4th just fine. (I'm thinking some bit of trash might be in there?).

Anyway, if you guys can help me sort this out it would be great. If I get it running smooth without paying an arm and a leg I'd like to see how far this car can take me! 30 MPG is very nice.

Thanks in advance for any suggestions.

~ S

[tahiti350]

The main trans connections are right by the aft engine torque link between the engine and firewall. 2 Big square plugs. I know this because I just pulled a trans at the wrecking yard for my '92....

[Skube]

Yeah, I pulled the passenger side connector apart to check the inhibitor switch operation. I haven't pulled the driver's side yet. I'll do that next.

Any idea where the front speed sensor is?

[tahoe.ss]

skube, any news on what it could be???

i've got similar trans problems that maybe "go away" and come back also.

[Skube]

My speedometer cable broke, and when I replaced it the problem went away. I later found out the vehicle speed sensor is in the speedometer! Makes sense. The TCU needed that input to tell the tranny to shift up from 2nd. I guess 2nd is "limp home" mode?

~ S