1994 GMC 5.7 crank but loses spark and won’t start

[murguia]

Hey everyone,

Hoping to get some help. I have a beautiful 94 gmc with a 5.7. Got it off the original owner 5 years ago and never had one issue with it until recently. Was running perfectly fine and then wouldn’t start. Was just getting a click… here’s what I’ve done so far

New starter
New Battery Cable
New ICM
New Rotor
New Cap
New Coil

It ran great for two weeks but then it started doing it again. If I let it sit overnight it will start up and run well for about 10 minutes, then it just dies. Not gradually, it just instantly dies.

I checked the spark at the coil and it has spark after sitting for a bit but then the spark stops.

What in the world could it be?

THANKS

 

[Schurkey]

Distributor pickup coil and/or the magnet assembly
Faulty ignition switch
Loose/corroded/damaged wire harness to ignition coil, or between distributor/ECM/Coil

 

[murguia]

I did notice the original owner set it up with an msd ignition. The coil only has one plug going into it, even though there’s two sports for plugs. Is that normal?

 

[murguia]

It’s dirty in there. These were the old cap, rotor and coils before I replaced them all earlier today.

 

[Schurkey]

Distributor vent screen look plugged with corrosion--may be causing ozone to build-up inside the distributor cap. Clean the corrosion off the screens.

Verify the magnet in the pickup coil area isn't cracked.

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I don't know what the white-ish deposits are on the cap 'n' rotor. Can't be good, anyway.

The lack of a second connector body at the ignition coil is perhaps due to the modification of the ignition via MSD. It may be that the prior owner has disabled computer spark control, which is likely where a majority of your problems come. I see numerous wiring harnesses disconnected in your photos.

Pictures of the MSD system?

MSD spark-boxes are not known for reliability. MSD actually makes switching systems so that when one MSD spark-box fails during a NAPCAR or other long-distance race, the driver can quickly swap to the OTHER MSD spark box already installed in the vehicle for exactly that reason.

 

[murguia]

Replaced the entire distributor unit and it seems like it’s good to go.

Thanks for all the help