Intermittent No Start

[Jickey]

'91 5.7 TBI
I am stuck guessing. Every so often my truck will crank but no start. Give her some time and she'll start up. I have made it through some diagnosis and have concluded the condition is no spark and no fuel (no injector pulse). Every time I get involved in diagnosis she'll start-up, leaving me frustrated. I have tested the ignition module and tested ok but who knows, as soon as I reinstalled she started. Can anyone tell me how involved the ignition module is with injector pulse? I am assuming very involved. I'm getting ready to throw one at it. I hate throwing parts at a problem but with no wiring diagram and an intermittent condition I don't know where else to go besides the ECM and I'm definitely going ign mod first.

Any help is appreciated

 

[dmanblazer]

Msd 6al

 

[dyeager535]

Anything that keeps the ECM from seeing the distributor reference pulse can cause a no-pulse issue. (no spark means no pulse, whether it's bad module, coil, pickup, etc)

"Crank no run" links:
http://coloradok5.com/forums/showthread.php?t=141717&highlight=troubleshooting

Difficult with intermittents, however, it may get to the point where it is 100% consistent. Make sure to do a good visual, and check all connectors for good contact.

Spend the money on a GM module, the aftermarket ones are NOT well liked for durability reasons.

 

[imiceman44]

'91 5.7 TBI
I am stuck guessing. Every so often my truck will crank but no start. Give her some time and she'll start up. I have made it through some diagnosis and have concluded the condition is no spark and no fuel (no injector pulse). Every time I get involved in diagnosis she'll start-up, leaving me frustrated. I have tested the ignition module and tested ok but who knows, as soon as I reinstalled she started. Can anyone tell me how involved the ignition module is with injector pulse? I am assuming very involved. I'm getting ready to throw one at it. I hate throwing parts at a problem but with no wiring diagram and an intermittent condition I don't know where else to go besides the ECM and I'm definitely going ign mod first.

Any help is appreciated

Your problem might be a bad contact somewhere, a good cleaning of all contacts and maybe some contact grease before starting to throw parts at it.
When there is a bad contact, it gets hot and then you lose contact, it cools down then you have contact.
Just a possible scenario.

 

[Thunder]

If the ignition checks out ok. One other thing to check is:
It could be your fuel pump relay going bad.
When the relay goes out you have to crank on it for quite a while before the oil pressure switch sees pressure and closes allowing the vehicle to start.
But you usually have spark if the relay goes out. But it could be a combination of things giving you problems.

 

[dyeager535]

Easiest test for the relay is to have someone turn the key to "run" when the truck has been off for a bit, while you hang out near the tank and listen for the pump running. It's only about a 2 second prime, so pay attention. No pump, no relay.

My trucks pump is loud enough I can hear it from the drivers seat, but I don't know as the stock truck pumps are, especially if all the interior trim is in place.

 

[Jickey]

With no injector pulse and no spark I dove into the distributor. Attached is what I found. (Check out the crack in what I think is called the reluctor) It also felt like crap. I threw a distributor at it. I didn't bight the bullet for an MSD or something. The Chevy parts counter said it's discontinued. Went for cheepo from O'Reilly's. The hardware looked ok. I'm still gritting my teeth about the module it comes with. She runs ok so far. I'm hoping the crack is the culprit.

Thanks everyone for the ideas.

 

[dyeager535]

You can always pull your old module and keep it as a spare. I can see the yellow (or is it white?) "button" in pic 2 on the module.

Supposedly when the module is bad, this button pops up. Normally it's flush with the module, apparently a failure will somehow make it raise up. I've never seen ANYTHING in print about this, but it is certainly not just paint, nor is it of the same plastic as the rest of the module, so no other thing I can think of as to what it is.

I've yet to have a module fail, so I'm not sure what it is SUPPOSED to look like when it fails. All mine are rounded, but not protruding from the module.

 

[Jickey]

Interesting… Yea it's flush. I'd really like to pull the module and keep it for a spare but I don't know if I will get my $50 core back. Maybe I'll try.

 

[4X4HIGH]

The sad part about buying a distributor is the pick-up coil and the module are not new pieces, they are tested good used parts. If you don't believe me go back and ask the people you bought it from. If they are an honest store they will tell you.