91 Suburban dies when hot **SOLVED**

[91burg]

This is my first post and I'm stuck in Oakhurst, CA trying to get home to Los Angeles.

91 Suburban V2500 has been pretty much rebuilt over the last 2 years (see below for what was replaced related to the engine). It started stalling on us a few days ago when it gets hot. After it cools down, about 30 minutes, it starts and runs fine but only for about 15- 20 minutes, then it stalls out again. No fuel sprays from the injectors when it dies. I didn't check for spark, I have limited tools, but I did replace the fuel filter, fuel pump relay, ignition control module and swapped out the coil. I also replaced the fuel pump. None of this worked. There are no codes, just the standard flashing 12. I borrowed a scan tool from Kragen, but it wouldn't get a proper reading or read any codes. It's not over-heating and the gauge show normal temp when it fails.

I've been rebuilding the truck over the last 2 years to get to a dependable condition so we can tow our trailer. Following is a list of what's been replaced over the last 2 years (related to the engine):
383 Blueprint engine
Reprogrammed chip from Blueprint
Edelbrock headers
Flowmaster exhaust system
Edelbrock intake manifold
TBI components including TPS, injectors, regulator
Distributor - stock GM from NAPA
MSD coil, high temp coil wires, new cap & rotor

I appreciate any suggestions or advise. My next option is to take it to a local repair shop tomorrow - I dread that as I typically do all my own work.

Thanks

 

[dyeager535]

First, carry a noid light of some type with you. You can make one out of a dash bulb. When it won't fire, connect the noid light to each wire of the injector connector. The ECM GROUNDS the injector lead, so there is always 12V to the injector with key in run (*or should be*) however the light is used to indicate that the ECM is actually grounding the injector as the motor is cranking. Testing for spark gets you part of the way there, but not all the way.

My bet is that it is not. That tells you that the ignition module is the LIKELY culprit. If it's happening after running for awhile, $20 says that although auto parts stores can test them, the module won't test bad. Also check all components under the cap, such as the wiring/connectors.

If the light *does* blink during testing, something else is going on.

 

[Mountain_man]

I don't know if this helps or not but I had a fuel pump going out that had the same problem. Would run great for 20 miles or so then just die. Once it cooled off it would run great again. Then one day it just wouldn't stay running at all past idle.

Also as other poster said check ignition module.

 

[91burg]

I fixed it and am now home with a happy family. The problem was with the pick-up coil in the distributor - which was a new GM replacement 2 years ago from NAPA. After replacing the ignition control module, the next sensible thing to check was the pick-up coil. I had to remove the distributor and the shaft to replace the coil. Nice design GM. $25 dollars and Back on the road after readjusting the timing back to 0 degrees. Runs great.

Just so you know. Ignition modules are common, but if not that, check the pick-up coil.

 

[resurrected_jimmy]

Congrats on getting it solved and posting up a resolution to the issue

 

[CGT80]

I had a similar issue and fixed it a couple weeks ago. I run an MSD probillet hei distributor on a 79 chevy 385 engine. Sometimes it would not start and other times it would. I ended up wiring direct from the battery to the distributor and sometimes it would only start after connecting and then disconecting the wire a few times. One time the engine turned a bit when I connected the wire, without hitting the starter. I finaly ended up changing out the pickup coil and it solved the problem.

I ordered an msd pickup coil from summit that was supposed to fit all msd distributors. Well it didn't. The msd hei distributors use the stock hei style pickup.

Im glad you got your truck fixed. I hate chasing down electrical grimlins.