HELP!! 94 80 Series Check Engine Light if Not at Operating Temp

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Spurman98

Spurman98

Joined
Mar 27, 2025
Threads
2
Messages
6
Location
Alabama
Hi All, I'm having some issues with my 94 80 series I bought a year ago. Truck has run great since I bought it, recently though it has been having issues with going into what feels like a "limp mode" if I dont let it warm up to operating temp before driving. It started back in November when I got back from a week long trip and I decided the truck needed to be ran since it had been sitting for a week. I didnt let it warm up and as soon as I pulled out of my driveway and accelerated, the check engine light came on and I immediately lost all my speed and RPM's. Trying to accelerate again, it revved up to 4000 rpm's and hard shifted into what I assume was second gear. It would shift all the way through but had very low acceleration and would always get high rpm's before hard shifting to the next gear. I took it back home and let it warm up the next time I drove it and had 0 issues with it. It's happened several times over the last couple months and the other morning I had to shut it off on the side of the road, re crank and let it idle until it got to operating temp before I could go anywhere in it. I know its a simple fix of "let it warm up before you drive it anywhere" but there is obviously an underlying issue causing this and I'd like to fix it. The check engine light does not come back on if you turn the truck off so I can't check the code by jumping the E1 and TE1 terminals. I have racked my brain and cannot figure out how to fix this issue! I am not super mechanically inclined but I am trying to learn with this truck so any help would be greatly appreciated.

Current Maintenance done
1. New air cleaner hose 2 months after purchase
2. New idler pully and belt for AC compressor done 6 months ago.

Thanks in advance for any help!
 
First check you trans fluid level, if you don’t know how to do that download the FSM (Field Service Manual) from the resources section on here for free. Your truck should not be slipping gears regardless of engine operation. After that follow back up. Don’t be afraid to ask questions but also do some work on your end we can help you but you got to help yourself also. Welcome
 
Don’t turn the truck fully off then read the codes
Fsm has troubleshooting chart have you checked that out? Can download here for free on the site
 
You've already gotten some good advice here. Its an OBD-I truck, but you can still get codes from your inspection port. You need to learn how to get the codes, and how to decipher the codes. Like others mentioned the FSM will tell you most of that.

While checking your fluid level of the trans, also check to be sure your throttle cable for the trans isn't broken. Luckily for a 94 they are still available. But I'm thinking this probably isn't the issue.
 
Trans fluid was fine after following the RSM instructions for checking. Got a code-55 for a rear knock sensor after taking ajax advise. Currently waiting for one to come in and replace to see if this fixes the issue. I did try the diagnostics section of the RSM but I could not find anything that resembled my specific issue. I will try to dig a little deeper and will update after replacing the sensor.
 
Replaced the rear knock sensor about 2 weeks ago and have been daily driving since then. I have driven the truck multiple times without letting it warm up to operating temp and I cannot get the issue to recreate itself. Thanks for everyone's help on this. It's nice to finally have the truck running right again.
 
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