Question about 1997 GMC Jimmy

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97 jimmy runs when you pour gas into throttle body, fuel pumps is putting out 55 to 56 psi. but will not pickup the gas from the injectors, fuel manifold psi is 55 to 56psi. 1997 4.3 vortec engine

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  • mdddinc Oct 18, 2010

    97 jimmy runs when you pour gas into throttle body, fuel pumps is putting out 55 to 56 psi. but will not pickup the gas from the injectors, fuel manifold psi is 55 to 56 psi. when the gas is burned out of the intake it will not start or run till you pour more gas into it. 1997 4.3 vortec ingine

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  • GMC Master
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If the 8th letter of the VIN # is W which i bet it is than your fuel pressure is to low.

This engine uses a CPI unit to deliver fuel to the cylinders. The CPI unit consists of a central injector that feeds fuel to the poppet valve that are right above the intake valves. The poppet valves require high fuel pressure in order to open and deliver fuel to the cylinders at start up.

The reason why it starts and runs if you add a little gas through the throttle body is that once the vehicle is running the intake is under vacuum. The poppets can open with less fuel pressure in a vacuum. This is a real common scenario with these style injection systems.

A new good quality fuel pump (a/c delco or delphi are good pumps) and your fuel pressure should be back into spec of 58 psi or more and the vehicle should fire right up. Make sure you replace the fuel filter when you replace the pump.

Posted on Oct 17, 2010

  • 3 more comments 
  • Jeremy W.
    Jeremy W. Oct 19, 2010

    I'm sorry I misunderstood. I though it would stay running after you added fuel.

    The CPI units are or where common to fail back in the day. I think your next step is to pull the plenum and Check resistance of the CPI injector and make sure there is injector pulse to the injector. I don't recall the ohm spec for the injector off hand but I can get it if you need it.

    Fuel pressure still concerns me. Literally a pound can make the difference between starting and not starting. 55-56 should be enough fuel pressure to keep it running after it starts so I think at this point investigating the CPI unit is the best direction.

  • Jeremy W.
    Jeremy W. Oct 19, 2010

    I should also add that you need to check the injectors (there are six of them) not the injector. If the plenum is plastic you can pull the bulk connector and check them without pulling the plenum.

    Also make sure there is power at the pink wires in the bulk connector. This is power to the injectors. It is supplied by the ECM ingnition fuse which powers more than the injectors. If it was blown I'm confident the vehicle would not start since it also supplies power to the ignition module and the hall effect (cam) sensor in the distributor.

  • Jeremy W.
    Jeremy W. Oct 19, 2010

    injector resistance should be 11.8 to 12.6 ohms cold.

  • mdddinc Oct 23, 2010

    got battery voltage to all pink wires in bulk connector and each injector has right at 12.6 ohms

  • pbylsma Aug 05, 2012

    could you post if and how this was resolved?

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