Got a 502 MPI VST style motor that will have fire for 4 or 5 seconds then doesn't. Changed the coils, ignition modules, checked all grounds etc...

Any ideas??

Thanks

Capt Ross

I had that problem once and it was a ground. Triple check those where they are crimped.

Also check your ten pin for corrosion or loose

not to second guess you, but are you certain it is the ignition ? as noted earlier in many places here, the hi pressure pump will run during cranking to start the motor. that will let the motor start for a few seconds as you note but if the "run" circuit in the ecu doesn't tell the fuel pump that the motor is actually running then it will shut the pump off. if you are saying that you start it and it stalls, start it and it stalls over and over then i might suggest you hot wire the pump real quick as a test just to see if it stays running.

you saying it only runs when your cranking the engine then shuts off? a bad ignition module will bypass when cranking allowing it to start then when you let go of the ignition it shuts off.. Is this the case?

Changed modules from another runnin motor.... wasn't it...

Did you put a fuel pressure gauge on it to be sure the pressure doesn't drop just before it kills?
Eddie

Using a spark board to see the fire - then it just goes away ...

you were right - overlooked where it was pinched - but not cut......