91 chevy truck wont start sometimes. some times from cold start truck will not start but after

1 ANSWERS

1. pabitraghadai
   

   hi there,
   
   I suggested you check those items, not replace them. They can be tested, and I hate to see people just throw money at a problem, even though it occasionally catches the problem.
   
   The way you say yours does, makes me think the fuel pump isn't running by relay power, but by oil pressure power. There is an oil pressure switch that provides power to the fuel pump once oil pressure builds to 4 PSi.
   Now, don't replace that switch. If that is what's happening, the switch is ok.
   
   
   That is why I asked if the pump runs when you turn the key to run. It should come on and run for two or three seconds.
   If it doesn't, then there are a couple possibilities, but check it first.
   
   If the pump does run, I personally would like to test the pressure, to see if it is up to spec.
   
   If the pressure is correct, and there is spark, which I assume there is if it starts with a prime, then I would look at the control system for the injectors.
   
   It is remotely possible you are getting some vapor lock in the injectors from heat soak, so if the pump does run with the switch in run, try cycling it to run for three seconds, off a few, run for three, etc. and see if that will circulate some fuel through to cool them.
   
   
   
   There is a hot start module for some of the larger engines just for that reason, that runs the fuel pump for seven seconds.
   
   best of luck

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