Hey guys, I recently bought a 1993 C2500 with a 5.7 and a 4l80e with 145k from a neighbor who was the owned the truck since 1998. The truck is in overall decent shape but one consistent problem are the shifts that feel like the transmission is going to evacuate from the truck. The PO said that he had taken it to a few transmission shops and they mostly said that its normal operation even though it feels awful. As far as I know its the original trans and the PO said that its been shifting like this for at lest 10 years and hasn't failed yet. I Bought the truck very cheap and I have no use for it and I'm looking to sell it after I clean it up a little, but I'm concerned the shifting will put off any buyers. I just put a new AC Delco TPS on and test drove it and it shifts very late now and on top of it still being harsh. After the new TPS the engine light came on also and I have code 22, I also noticed when put I the new TPS on I had to turn it clockwise to get the holes to line up. When I first set it one the little dowel it sits at about the 11 o'clock position and I had to rotate it so I could install it. This is the same with the new and old sensor. I cant find any info on this hence why I'm writing this.I tested the TPS voltage and I got 0.46V closed and 4.2V at WOT for BOTH the old and new sensor. I have disconnected the battery cables and held them together of 30s and that had no effect. I know another cause for a hard shift is the fuel filter but that was replaced not long ago as the PO kept up with the truck quite nicely. Thanks
93 C2500 shifting hard
- Thread starter Peaches
- Start date
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stutaeng
I'm Awesome
Um, not normal at all to be doing harsh shifting. The shifting late is probably because it has some numerically high gears. My truck 4.10 does this. I was used to driving another truck with 3.42, so I also thought it was unusual when I bought the one with 4.10s.
So the code 22 came on after you changed the TPS? Why did you change the TPS? And is the replacement the correct part?
Not sure what to tell you, short of dropping the pan and at minimum changing the filter and new fluid.
So the code 22 came on after you changed the TPS? Why did you change the TPS? And is the replacement the correct part?
Not sure what to tell you, short of dropping the pan and at minimum changing the filter and new fluid.
I changed the TPS because from what I read it was a common and cheap solution to my problem. The old and new sensor look exactly the same but now it shifts at like 1000 rpm more than what it used to with the old sensor. Basically my issue is I tried to fix one problem and made another even though I didn't fix the first.
1ton-o-fun
Automotive Durability Tester
I thought the PO installed a shift kit or something in my '93... it spins the tires on the 1-2 shift at part throttle if it's raining. But, my coffee has a lid and my other car has shifts you can barely notice, so I can live with it. -As long as it stays healthy.
BTW, same as yours, Peaches. '93, 5.7, 4L80E. Mine has 4.10 gears.
BTW, same as yours, Peaches. '93, 5.7, 4L80E. Mine has 4.10 gears.
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stutaeng
I'm Awesome
Without checking the transmission fluid line pressures, not sure how you would properly diagnose it. It may be an electrical part of the engine causing this, or an electrical part of the transmission itself.
But I don't know how you still have the Code 22. That needs to be addressed before you go down any rabbit hole...Hash shifts are usually because the ECU has detected a slip (can be rear or perceived due to a faulty sensor giving wrong data) and commands maximum line pressure.
But I don't know how you still have the Code 22. That needs to be addressed before you go down any rabbit hole...Hash shifts are usually because the ECU has detected a slip (can be rear or perceived due to a faulty sensor giving wrong data) and commands maximum line pressure.
Supercharged111
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After replacing the TPS you need to do a TPS relearn. This happened to me and the trans maxxed out its line pressure. For me, a relearn consisted of a PCM flash, but I know there are other, simpler, DIY methods. If you search it for an LS1 you should find your answer. A failed MAF will also cause this.
Don't know if this will help as it is a 99 Vortec I have not TBI but when I was asking about hard shifts (now confined to 3rd to OD shifts for whatever reason) I was told the PCM reads from the MAF sensor as well as others and that the MAF sensor has a big influence on shift quality. Given how susceptible to dirt and damage they are - worth checking yours is as it should be?
stutaeng
I'm Awesome
Ditto on the TPS relearn...forgot there was that procedure. There's good articles on this website that show you how to do it.
Yes, a dirty MAF will also cause hard shifts, but pretty sure the TBI setup did not use MAF, instead it uses the MAP sensor? Maybe it worth a shot to test that one?
Yes, a dirty MAF will also cause hard shifts, but pretty sure the TBI setup did not use MAF, instead it uses the MAP sensor? Maybe it worth a shot to test that one?
Supercharged111
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Derr, good call. By the time I made my post I'd already forgotten about it being that old. With that said, I'm not sure if the TBI trucks used a relearn procedure or of you have to set it to a certain voltage yourself. If it's the former, I bet a PCM reset would do. The OBDI stuff forgets everything when you unplug it AFAIK.
Garrett Fulton
Newbie
My '93 C2500 started the hard shifting and it was a bad ignition switch. Bad switch had worn contacts and the green crud in it.
