1995 GMC Sierra

[Fishin Dood]

1995 GMC Sierra

5.7 Liter

Automatic

4wd

203,000 mi.

So my problem started out late this summer. One day I was leaving for work and the following happens. Engine starts great as usual, except Tach is not working and I cannot tell what gear it is in (indicator light for PRND321 is not on). I put it into reverse, it shifts HARD into reverse. I back up and put it in Drive it shifts REALLY HARD into drive.

I have to put it into Second gear (wont go into first) to get rolling. Once moving I can shift into 3rd to travel up to speed. I have no overdrive whatsoever. I drive to work shifting down at stoplights and what not.

After work I start it up and everything seems fine. I drive home and it shifts as smooth as it ever has. No problems. I drive it for a while without any problems (days or weeks)then it will do the same thing over again.

I changed tranny fluid and filter, but i suspect it is a bad connection (short) somewhere. I have had luck jiggling (lack of better term) the connection where the main harness goes though the fire wall to the computer behind the glove box. However, this doesn't work all of the time. Do you think the issue is in the connection at the firewall or is it the computer, or am I going in the total wrong direction??

[deadeye]

I know it seems like a odd thing to check first but make sure your battery is in good shape. I have had a few gm's lately that have had really odd stuff going on like that and it turned out the battery was shot/shorting out.

Assuming the battery is in good shape I would make sure your ground cables are clean and attached well. Its pretty common to have a bad ground causing that kind of whacky stuff too.

Moving on from there I would check the connector at the pcm (sounds like that might be the culprit) for burned/corroded terminals. Its not to hard to re-pin the connector if your comfortable doing that kind of thing. The tool to help re-pin it is like ten bucks and the pins are around 5 for a pack of them. Dont be afraid to use some di-electric grease on the connectors too.

[Fishin Dood]

Thanks for the reply Deadeye. I actually replaced the battery last week (it was junk). And the latest episode of the truck acting up was this weekend. I will check on the grounds and then look at the connector. Anything else I should look at??? Thanks again for the help I really appreciate it!!