Here's the story (warning: long post)
Bought the truck ('91 crew cab) this past December. Supposed to have a rebuilt trans (4l80e). The torque converter would unlock on occasion on long trips, but not often. Thinking caused by a faulty brake switch.
Other than that, the truck ran fine until about a month ago. I took the truck about 1.5 hrs away with an empty trailer to pick up a suburban and some other stuff. Started home with the somewhat heavy load, keeping the trans in 3rd. About half way home I stopped to get gas. The truck was running a bit hot, but nothing I was concerned about. Pulled back onto the highway but the truck wouldn't shift out of second. Ended up getting trailered the rest of the way home.
After some research I found out the truck was going into limp mode. I could make the truck shift to 1st, but nothing else. I started by pulling the connections on the trans. One was a little dirty, so I cleaned it. Also checked the fuse, which was fine. The fluid looked nice and pink, too. Test drove it and it shifted like normal. Drove it for a week with no issues.
After that week, I went back down to get the rest of the stuff I had bought with the burb. Hooked on to a trailer there and took off down the road. Immediately the truck went into limp mode. I was able to get it shifting normal by down-shifting to 1st and slowly shifting through the gears. Stopped right after that at a gas station. Left the station and it immediately didn't shift again, but was able to manually shift it back through the gears again. Didn't stop on the way home.
Unhooked the trailer and it still wouldn't shift, even manually after manually shifting. Pulled the connections and cleaned them and put some electric grease on them. Started shifting normally again.
Dropped my son off at the sitter one morning. When I started it to leave, it wouldn't shift and I haven't been able to get it to shift normally since.
I also changed the shift solenoid B. Still nothing. I can't manually shift into 1st now, either.
From my research, here are the possible causes:
Throttle position sensor (tried checking this but couldn't figure out how)
VSS
Shift solenoid B (replaced)
Bad connection at the pass-through (**edit** checked wires running to the pass-through - 12 volts at pin E, have not actually checked the pass-through itself on the transmission side)
Bad ground somewhere
At this point, I'm pretty frustrated. I picked up a multimeter to check everything with, but I'm new to vehicle electronics (and multimeters, for that matter) so I'm not real sure on what I'm doing. I'm getting ready to do a 4wd conversion and would like to have this issue solved before I get started. I also have a 4wd unit sitting on the floor that I could rob some sensors from if necessary. It's supposed to be a good, low mileage unit that I'm using for the swap.
I'm willing to check whatever I need to. I just need some very detailed help.
Bought the truck ('91 crew cab) this past December. Supposed to have a rebuilt trans (4l80e). The torque converter would unlock on occasion on long trips, but not often. Thinking caused by a faulty brake switch.
Other than that, the truck ran fine until about a month ago. I took the truck about 1.5 hrs away with an empty trailer to pick up a suburban and some other stuff. Started home with the somewhat heavy load, keeping the trans in 3rd. About half way home I stopped to get gas. The truck was running a bit hot, but nothing I was concerned about. Pulled back onto the highway but the truck wouldn't shift out of second. Ended up getting trailered the rest of the way home.
After some research I found out the truck was going into limp mode. I could make the truck shift to 1st, but nothing else. I started by pulling the connections on the trans. One was a little dirty, so I cleaned it. Also checked the fuse, which was fine. The fluid looked nice and pink, too. Test drove it and it shifted like normal. Drove it for a week with no issues.
After that week, I went back down to get the rest of the stuff I had bought with the burb. Hooked on to a trailer there and took off down the road. Immediately the truck went into limp mode. I was able to get it shifting normal by down-shifting to 1st and slowly shifting through the gears. Stopped right after that at a gas station. Left the station and it immediately didn't shift again, but was able to manually shift it back through the gears again. Didn't stop on the way home.
Unhooked the trailer and it still wouldn't shift, even manually after manually shifting. Pulled the connections and cleaned them and put some electric grease on them. Started shifting normally again.
Dropped my son off at the sitter one morning. When I started it to leave, it wouldn't shift and I haven't been able to get it to shift normally since.
I also changed the shift solenoid B. Still nothing. I can't manually shift into 1st now, either.
From my research, here are the possible causes:
Throttle position sensor (tried checking this but couldn't figure out how)
VSS
Shift solenoid B (replaced)
Bad connection at the pass-through (**edit** checked wires running to the pass-through - 12 volts at pin E, have not actually checked the pass-through itself on the transmission side)
Bad ground somewhere
At this point, I'm pretty frustrated. I picked up a multimeter to check everything with, but I'm new to vehicle electronics (and multimeters, for that matter) so I'm not real sure on what I'm doing. I'm getting ready to do a 4wd conversion and would like to have this issue solved before I get started. I also have a 4wd unit sitting on the floor that I could rob some sensors from if necessary. It's supposed to be a good, low mileage unit that I'm using for the swap.
I'm willing to check whatever I need to. I just need some very detailed help.
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