95 ecsb 2wd 5.7 4l60e. Truck does one of three things. It runs fine for days. Or i will start it and it goes nuts idling at 1300 with the iac stuck wide open. It also locks the trans in 3rd gear. I can manually pull it into first and then shift to third but no second or overdrive. The other thing it has done twice now is while driving normally, it will suddenly drop into third gear. Ill pull over and it will sit and hunt for an idle between 900 to 1100 with a normal rythm. Again the same condition with the transmission. Check engine light is on steady in both cases. Also when this happens, it will not go into diagnostic mode with a paperclip. I can't predict when its going to happen. It has nothing to do with hot or cold starts. And it fixes itself everytime. The CEL will go out and then its fine. Once that happens I can pull the codes. It throws one for everything on the list of codes. So my immediate thought was bad grounds. Cleaned those thoroughly. Still does it. This has been going on for 2 weeks. I cant force it to fail and i also cant get it to run right. It just fixes itself. Ignition switch maybe? My only concern there is its not exhibiting the common symptom of a screwy gauge cluster or prndl. If the ecm was bad it would just be bad right? Im pulling my hair out. Its my DD and i drive 100 miles round trip every day for work. Thats a long way to be stuck in limp mode when it acts up.
Need help bad....again
- Thread starter dgumoe
- Start date
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mistaake
Real Name: Michael
I'm not expert but that definitely sounds like an electrical/sensor issue. So you are saying that you don't just get a few codes you get every code there is? To me that screams bad ECM. Did you check the connections to that? Do you have the resources to go to your local junkyard and buy a unit there? It has to be from a 95 because that is a weird year in that many electronics and other stuff do not swap over to any other year. I guess it was a transitional year before OBD2.
Yes, 95 is all on its own. Ive considered the computer being at fault but I dont believe it to be only because its intermittent. The plugs are secure. I may have exxagerated about "every" code. It threw so many that i lost count. At least 15 of them. Im leaning towards the ignition switch being at fault right now but I cant verify it until the truck goes batso again. I cant force a failure no matter what I try so right now I am just stuck in automotive purgatory waiting for it to fail again. My test light is on the floor waiting patiently. If the switch wasnt 130 bucks i would just replace it but for that kind of money I want to be sure.
mistaake
Real Name: Michael
What if you go on a really bumpy road does it have the problem? It can't possibly be random. Sometime I know from working on computers (PCs, not car computers) is that it is never random and there is always something causing it.
Its only happened twice while driving. And both times its on a smooth highway. I made it to work today with no hiccups. Went to leave for lunch and it was doing the high idle thing again. So i checked all the fuses for power and everything is lighting up. What i didnt do is get voltage readings because i didnt think about it till just now. I will go out there again on last break and see what it does then. My luck is it will be normal again and i wont get to troubleshoot. The local upullit is showing multiple trucks my year in the yard so i may have a fighting chance to get an ecm tomorrow if i decide thats the next course if action. Based on the test light, I am ruling out the ignition switch unless i get less than system voltage when i check with the meter.
NotARealK2500
This'll be my last GMT400, I swear!
Intermittent issues tend to indicate electrical faults.
The transmission is apparently throwing itself into third gear, so it's going into limp mode, where both your shift solenoids are in the "off" position. (i.e. - "self preservation mode"), but it doesn't sound like a transmission issue - sounds like a bad reading being given off by your PCM, as a result of a sensor.
When was the last time your TPS (if ever) was changed? MAP?
The transmission is apparently throwing itself into third gear, so it's going into limp mode, where both your shift solenoids are in the "off" position. (i.e. - "self preservation mode"), but it doesn't sound like a transmission issue - sounds like a bad reading being given off by your PCM, as a result of a sensor.
When was the last time your TPS (if ever) was changed? MAP?
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I have multiple spare sensors that I've collected. I swapped the tps when this first started but the problem persists. Found a good ecm at the upullit this morning and just put it in. Truck is running like normal right now. All I can do is drive it and see if it fails again. If that happens then i get to start chasing wires. Oh boy.
