Mom need help!! 96 Chevy 1500 cranks but wont start

Discussion in 'Chevy Truck Forum' started by Jelaine3, Jun 1, 2010.

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  1. DaveDanger

    DaveDanger Senior Member

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    Jelaine3, I've discovered in troubleshooting fuel pump problems of my own (96 Silverado Pickup) recently that there's several possibilities that can make that engine crank over but not start.
    The following 2 items are not the only things that can affect your son's problem, but they need verifying.
    The fuel pump receives electrical power thru a parallel circuit; it begins when the key is turned to the run position by sending current thru a relay in the "underhood relay center". The relays (about 4 or 5 depending on how the vehicle is equipped) are labelled inside the top cover of the relay box. They simply plug in and pull out as necessary to test or replace. The fuel pump relay is a 5-pin relay, and powers the fuel pump during the start process. As soon as the engine does fire and run, oil pressure should build up almost instantly. When it reaches at least 4 psi, the oil pressure switch becomes the circuit that provides electrical power to the fuel pump, and supposedly the fuel pump relay goes to sleep, un-needed during the normal run. (I'm not 100% convinced the relay does this, but that's a whole 'nother story!)
    The oil pressure switch is considered the safety switch in the event of a crash. An impact that is sufficient to stop the engine also stops the oil pressure when the engine quits. The electrical power is removed from the fuel pump and fuel is not being pumped all over a hot, possibly sparking engine.
    Verify that the relay is providing electrical power to the fuel pump when the key switch is turned to the run (not crank) position. It should run the pump audibly for about 2 or 3 seconds. I've had old and new fuel pumps in my truck, and I've been able to hear them all if there was not a huge amount of ambient noise. The radio on at normal volume is enough to hide the pump noise.
    Verify that the oil pressure sending unit is plugged in properly. It's right down under/behind the distributor. It would be very easy to have disconnected that while working on the distributor, and missed reconnecting it.
     
  2. Jelaine3

    Jelaine3 Member

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    ok so the oil switch/sending unit is basically a sensor? and having had all sorts of oddball sensors in diff vehicles go bad over the years, if this quit working while we were driving would it have caused the pump to quit and therefore the truck to just die? I get the part about how it stops the pump after an accident--so along those lines when the engine unexpectedly quits for mechanical reason, does it also cause the fuel pump to shut down and perhaps not let it restart? how is the switch "reset"? We know the fuel pump initially starts up via the relay we can hear it. but if the oil switch isnt working, or is "off" is that preventing the fuel pump from making the changeover to the other circuit to keep it running?
     
  3. DaveDanger

    DaveDanger Senior Member

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  4. howardsternyaho

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    well from what its sounding like is the timing is a bit restarted or to far advanced as for doing anything to the valves id run a compression test across the cylinders before i went digging internally if at most it could be a bad crank position censer but i would think that a code would come up for it if all else fails id look into disconnection the remote start iv had many bad things come into play with diy install jobs if need be as a off beat idea to keep in mind is see if you cant strip the electronics back on it to run on the moter its self
     
  5. Jelaine3

    Jelaine3 Member

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    Thank you to everyone who responded and offered help. Mechanic found that distributor had jumped 180 again, so further tear down found a bad cam that's allowing the distr to jump and slip, and thus the timing issue/no start. sooooo......now we're looking for a cheap motor to drop in it. thanks again!!
     

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