1993 C1500 Odd Problem

John Mayfield · August 2, 2019

So i would like to start at the beginning. So i bought this truck with 160k miles in 2013 and it needed a alternator and battery. everything had been just fine until the middle of 2017 when it made high pitched tones, well i found out that the throttle body intake gasket was sucking in air and it was making a whistling sound. so i pulled it apart, cleaned it up a bit and replaced the gasket. everything was fine for awhile.

early 2018 the truck would randomly start to idle too high when at a slow speed, or stoped at a traffic light and it would rarely return to normal speed until i turned the truck off and started it again, this problem always came with a check engine light, usually turning the truck off and back on that fixed the issue.. However if i tried to accelerate while it was doing that it would shift really hard.

some time in 2018 turning the truck off and back on did not fix the issue so i popped the hood and found a vacuum leak. So i replaced all the vacuum lines and the problem went away for the moment. But remained a occasional problem.

A month or two ago the problem became much more frequent, often happening twice per day. Thinking that the problem must be vacuum related i started replacing parts involving the vacuum system hoping to solve the problem. I replaced the PCV valve, EGR solenoid, Map sensor, and EGR Valve.

Now after reading a bit here and there online and talking to other chevy owners they recommended i replace the Transmission shift solenoids, which didn't look to hard so i did, i purchased this kit. https://www.ebay.com/itm/Transmission-Shift-Solenoid-Service-Kit-Filter-Gasket-A-B-Fits-93-97-GM-4L60E/351621567860?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

so i dropped the pan, drained the old fluid, replaced the shift solenoids, cleaned the old gasket off, cleaned the magnet with paper towels, cleaned the bottom of the pan with brake cleaner, and let it dry. then put it back together. I filled the transmission fluid back up with Castrol DEXRON VI Transmax Automatic Transmission fluid (says compatible with Dexron IIE) and everything seemed to be fine that evening.

Well the next day i drove my truck to work and some point through my trip something happened, i lost all torque and acceleration, from a dead stop it has no get up and go, even if i shift into 1st or 2nd gear it still accelerates the same way. The engine sounds normal, it's not revving faster or anything there is just no power being applied to the ground.

So i checked the level of the transmission fluid and it looked a bit high, not any higher on the stick than 1/4 inch or so, but to be safe i stuck a tube down the trans fluid filler and took some back out.

Nothing seemed to change.

I also noticed (but only after this issue) that the 10 amp fuse in the fuse panel labeled trans is popped. i replaced it and it popped again immediately.

I am not sure what to do next. i was thinking i should put the original shift solenoids back and see if the new problem goes away.. i am wondering of the replacement shift solenoids were garbage or not quite compatible, or perhaps they are causing that fuse to pop.

Jglew82 · August 2, 2019

Sounds like your new solenoid pack is shorting out which is popping the fuse. Double check you didn't get a wire pinched somewhere. Not sure why it was recommended to replace them in the first place. Did you pull your check engine light codes?

To me, this sounds like either an IAC or TPS, which were common failure points in TBI's. Bad TPS will cause a check engine light and trans shifting issues.

Edited August 2, 2019 by Jglew82

Bigfutz · August 3, 2019

High idle symptoms may be a sign the IAC needs to be reset. (I think you may have introduced a separate issue with your tranny solenoids.) There are more in dept procedures, but here’s one:

https://itstillruns.com/reset-baseline-idle-gm-tbi-7959677.html

John Mayfield · August 3, 2019

well i may of fixed one of the problems i was having. Today i decided to put the original solenoids back, while i had the pan off i inspected all the wires inside the transmission and they all looked just fine, nothing was worn, brittle or exposed, and none of the connectors were loose. so i put it back together. after i had that finished i inspected the wiring leading out of the transmission, well there is a clip that bolts to the bell housing near the engine that holds the transmission harness wires in place. I noticed the black loom tubing that goes around the wires was very weak and falling apart near that clip i removed the clip and found the clip had worn through the loom and jacket of the green wire and was making contact with it.

i wrapped everything with a thick layer of electrical tape and bent that clip into a more friendly shape and put it back.

the fuse is no longer popping, and the truck seems to be driving and shifting fine now..

i am still thinking that the old issue of intermittent high idle and hard shifting may exist, but i won't know until it happens again.