Hello all
I recently got a 87 XJ with the automatic trans and 240k miles for $500 that was running great until I power washed the engine bay while the engine was running. After the power wash I took it for a drive and about 2 minutes in it started behaving like a slipping clutch would, revs would increase but no power was being transmitted to the wheels. This was occuring at about 50 mph in 4th gear. And then it just wouldn't shift from 2nd gear. I looked through the forum and noticed other people had a similar issue and when they replaced the TPS it would resolve itself. I replaced the TPS with one from oreillys and adjusted it via cruiser54's method. Backprobed the input voltage of 4.66v and set the output to 3.87v. It now shifts but shifts into 4th gear way too early and can't handle any load without shaking and shuddering like there's no tomorrow. Even with full throttle it won't switch down into a lower gear. The transmission kickback cable has been adjusted and I can shift thru the gears while driving if I remove the fuse to the TCM. I also cleaned the ground connection by the dipstick and verified the vacuum lines were connected and intact. Transmission fluid is at the correct level and I have taken the connectors apart and cleaned them/sprayed with electrical contact cleaner. I'm at my wits end!!

 

See Tip 10 on my website.

 

I did that one too, it seems like the TCU is not getting the signal from the TPS and is shifting based purely on rpm and not load. When I check the output voltage from the TPS is it supposed to change when the throttle is modulated? Which wire on the TCU is the TPS signal?

 

Ah yes, death by pressure washer. The TPS really doesn't like having water injected into it.

An 87 has the dual output TPS with 2 connectors. The square connector is the one feeds the transmission computer and hence the shifting. The signal runs backward from the other flat connector used for the engine computer. Looking at an 88 wiring diagram, the black wire is ground, the gray wire is +5 volts, and the blue wire is the one that should change roughly 4-> 0.8 volts. See Cruisers tip 8 for more details on testing. http://cruiser54.com/?p=54

 

I generally disconnect the IAC and TPS, then stuff a large ziplock bag around them (including the sensors) to keep them dry when cleaning the engine bay. Avoid direct pressure around the TB.

 

I never use a power washer on a vehicle, it can be destructive, gets in electric bits, can damage paint, blows past seals, etc.... ugh..... Maybe to clean my concrete driveway, but not the jeep ever. Plus they are oft so freaking noisy. A regular garden hose spray noozle, a bit of dish soap, bucket and a rag powered by elbow grease*, so much nicer, much easier to use, less danger of destruction. That said, next time use the hose and cover the electric bits with plastic bags, tie or tape shut, and avoid directing water in such areas. The water pressure and flow from your garden hose usually is plenty for a good clean. And you can listen to music while washing, or the birds chirp, rather than having to wear hearing protection as with a power washer,

* if you got grease and oils to remove from engine or underside, then use a solvent like "Engine Bright or such, spray solvent on, let soak, wipe off excess with paper towels, then rinse with garden hose.

We didnt have these power washer things back in the day, and got by just fine, with less troubles.

good luck.

 

Yes, the voltage should change with the sweep.
Blue goes to TCU input from TPS