Any way to force ECU into limp mode?

[RecklessWOT]

Wondering if anybody knows of a way to get the ECU into limp home mode without the use of a scan tool?

The truck is an '87 suburban V10 with a 350. I've been having issues with it cutting out. Usually under load but sometimes it dies randomly while idling for a few minutes, and stalling from a start. Doesn't run rough or anything beforehand, just cuts right out. It never even throws a check engine code. I have gone through just about everything possible- full tune up, ignition module, TPS, IAC, MAP, coils, blocked EGR, got rid of all emissions parts, changed the fuel filter, checked grounds... I've got a GM service manual even the "fuel and emissions including driveability issues" supplemental book, chased it around every which way I can think of and still nothing. I had it narrowed down to only three last possibilities: Bad fuel pump, distributor, or ECU itself.

So I had a buddy hook it up to a scan tool and we took it for a drive just to see what was actually happening right before/when it died. Many of the sensors (even the brand new ones) would start randomly outputting funny readings, or lose communication alltogether. When I put it in limp mode, all of a sudden the problem was gone. It ran rich as all hell but it was actually driving around completely fine. So that means my distributor is fine as is the fuel pump and injectors. So that leaves me quite obviously with a wiring problem. I have literally given up on vehicles and used them for target practice because of wiring issues in the past. I can't fix electrical problems to save my life.

I am SO CLOSE to ripping everything off my truck, slapping on a carb and calling it a day. But until I am able to find the time to do that I still have to drive the truck the way it is every so often. I would like to know if there is a way I can put it in limp mode so I can actually drive the ******* thing somewhat normally in the meantime without stalling while taking a left across a busy street.

 

[quaddriver]

well an ecm for that is under $100 so dont throw our the baby and bathwater just yet.

It has been my experience that when EVERYTHING goes batshit at once, somewhere somehow a ground got futzy.

trace em, cleam em

 

[4WDKC]

Wondering if anybody knows of a way to get the ECU into limp home mode without the use of a scan tool?

The truck is an '87 suburban V10 with a 350. I've been having issues with it cutting out. Usually under load but sometimes it dies randomly while idling for a few minutes, and stalling from a start. Doesn't run rough or anything beforehand, just cuts right out. It never even throws a check engine code. I have gone through just about everything possible- full tune up, ignition module, TPS, IAC, MAP, coils, blocked EGR, got rid of all emissions parts, changed the fuel filter, checked grounds... I've got a GM service manual even the "fuel and emissions including driveability issues" supplemental book, chased it around every which way I can think of and still nothing. I had it narrowed down to only three last possibilities: Bad fuel pump, distributor, or ECU itself.

So I had a buddy hook it up to a scan tool and we took it for a drive just to see what was actually happening right before/when it died. Many of the sensors (even the brand new ones) would start randomly outputting funny readings, or lose communication alltogether. When I put it in limp mode, all of a sudden the problem was gone. It ran rich as all hell but it was actually driving around completely fine. So that means my distributor is fine as is the fuel pump and injectors. So that leaves me quite obviously with a wiring problem. I have literally given up on vehicles and used them for target practice because of wiring issues in the past. I can't fix electrical problems to save my life.

I am SO CLOSE to ripping everything off my truck, slapping on a carb and calling it a day. But until I am able to find the time to do that I still have to drive the truck the way it is every so often. I would like to know if there is a way I can put it in limp mode so I can actually drive the ******* thing somewhat normally in the meantime without stalling while taking a left across a busy street.

disconnect a major sensor ie TPS if you havent fixed it or ripped the EFI off of it yet.

 

[RecklessWOT]

disconnect a major sensor ie TPS if you havent fixed it or ripped the EFI off of it yet.

I had actually tried that, which was one of the things that confused me even more. But I did end up figuring out the problem, it really was the ECM itself afterall. Buddy of mine gave me a used one out of an old truck he had and it fixed the problem right away. Only thing is it's from a truck with a 305 so eventually I'd still like to get my hands on a proper one from a 350

 

[yevgenievich]

I had actually tried that, which was one of the things that confused me even more. But I did end up figuring out the problem, it really was the ECM itself afterall. Buddy of mine gave me a used one out of an old truck he had and it fixed the problem right away. Only thing is it's from a truck with a 305 so eventually I'd still like to get my hands on a proper one from a 350

I have one from a 90 suburban if interested. 350tbi/700r4.

 

[The88]

If it starts to randomly die again try to swap the tlp sensor. My 88 dis the same thing to the sounds of it and swapped the temp sensor and voia la