1995 k2500

Vincent Vangalio · January 18, 2016

I have a 1995 Chevy K2500 with the 5.7 and 4L80E. the truck has 147k miles on it. I have been having shift issues the last few days. It will stall under load with the break on when it is cold and it randomly wont shift. It either redlines or drops right down to nothing even with the peddle on the floor. If I let off and mash the gas it will pick back up but will not shift at the proper time if at all. If I shut off the truck and sit for a minute it will be fine after restart for a short time. This started less than a week ago and has gotten rapidly worse. Under the advice I received I have done a tune up on the motor, a trans flush and filter, and replaced the output speed sensor between Friday afternoon and this morning. After doing the trans flush and speed sensor this morning it rand great for about 10 miles. then started acting up again. I didn't think it was going to make it the last 5 miles to home. It stalled twice when breaking, would not shift unless I was WOT and then would not maintain gear if I let off and would have to hammer down again to get it to respond. I am considering replacing the input speed sensor tomorrow and I have heard that the TPS might be part of the issue. I am hoping one of you might know what is going on with this thing before I fire the parts cannon on the trans again.

Edit: 1/18/2016-Tested TP sensor this morning reading.43 key on engine off

green 788 · January 19, 2016

see if an auto parts store will read the service engine codes for you, there surely are some saved in the data base by this point in time.

some folks (even transmission shops) will tell you that you need a tranny rebuild--but be careful of that advice. Your transmission doesn't sound like it's actually slipping, so the problem is "communication" related most likely.

Do this... unhook the speed output (the thing you've replaced) and see how the truck drives then. That is supposed to put the transmission in a default mode. It'll shift hard (like it's got a shift kit in it), but you need to see if it shifts otherwise normally. With that sensor unhooked, it will shift a bit late as well, but it'll be a firm shift.

This will not render your speedometer inop; that sensor is actually on the transfer case, by the way.

With the tranny speed sensor unplugged, if the truck shifts through the gears then, and doesn't act up (other than the "snappy" gear changes which you should expect) then your next step is to figure out what part of the communication system is not working.

There is a large plug on the right hand side of the tranny, up sort of high. This junction can get transmission fluid in it, and cause the plug to get soft, and connections loose. I had a problem with my truck right in that area. I got sold a transmission rebuild, and found out only after the fact that the connection from the transmission which feeds data to the computer was the real culprit.

I doubt your transmission is needing a rebuild anything this side of 200k miles--unless it's been woefully neglected. The symptoms don't sound like bad clutches/bands... sounds more like electrical issues to me.

THORX4 · January 21, 2016

the 4L80E rarely needs to be completely rebuilt. It can be reapired in sections as I found out froma transmission shop. Wow gott tell you sound like a vaccuum under load. I know ther is not many vaccuum lines of that year like mine but id check it. Might also check the speed sensor. Most auto parts places will help you find codes.

Vincent Vangalio · January 21, 2016

I will try unplugging that sensor tomorrow. The truck has sat since Monday. I will also check that plug going to the computer. Hopefully we can narrow this down soon.

Vincent Vangalio · January 22, 2016

I unplugged the input shaft speed sensor today at work. The drive home was worse than the drive in. The truck even stalled twice while driving. I am thinking it might be related to the TP sensor. This time it kept acting like it was starving. The shift issue was not as bad as it was before but it was still there.

THORX4 · January 22, 2016

there is another option. Go to your local Midas dealer. Have them do a free safety check.

green 788 · January 22, 2016

okay, so the issue is probably not related to the tranny, since putting it into default mode (unplugging that speed sensor) did not change things.

yes, throttle position sensor could be a problem, fuel pressure regulator could also be causing this. Have Auto-zone or Advance or Oreilly's read the codes for you, and see what they say. This isn't always helpful, and sometimes it'll show a code for something that really isn't related to the problem... but often, it'll steer you right to the issue.

good luck.

Dan

Vincent Vangalio · January 23, 2016

So far I have had no luck finding anyone that has the scan tool for OBD1 and the MIL is not on

THORX4 · January 23, 2016

http://www.amazon.com/INNOVA-3123-GM-Code-Reader/dp/B000EVU8C0/ref=sr_1_4?ie=UTF8&qid=1453516256&sr=8-4&keywords=obd1+scan+tool

Vincent Vangalio · January 24, 2016

I will be messing with the truck more on Monday at work I ordered a new TPS and will also install it then. I am also going look into getting an OBD1 conversion kit for my innova diagnostic tool to see if there are any memory codes on the truck. I will post results when I have them.

Vincent Vangalio · February 20, 2016

I want to update everyone on my progress. I would have sooner but had trouble logging in. I figured out the issues it was not the transmission at all. I turned out to bethe fuel pump getting weak. I replaced the pump and tank and now it runs like a brand new truck. All the issues ended with the new fuel pump.