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'99 Silverado 5.3L No Start, Turns Over

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by FergusonT, Dec 15, 2012.

  1. FergusonT

    FergusonT Rockstar 4 Years 100 Posts

    One day this truck runs fine, no issues. The next day it turns over but wont start. Sometimes it would sound like it was barely starting to run before stopping. A few days ago I cleared a P0449 code thats been in there since I bought it in the spring of this year.

    When I scanned it after it wouldnt start it gave a code for MAP sensor, which I replaced. The old one had a grease like substance on it. But the truck still won't start with the new sensor. It seems like it could be a fuel problem, but I can hear the pump with the key on. I read some threads about passlock problems that sounded similar, but I don't get the security light like they did........about the same time I cleared the Evap. code I also replaced the battery. Ran fine for a few days then had the problem.
     
  2. j cat

    j cat Rockstar 4 Years 1000 Posts

    the 5.3L needs 53-62 psi to start. no codes check fuel pressure . pump running is quite common with low pressure.
     
  3. FergusonT

    FergusonT Rockstar 4 Years 100 Posts

    Ok, I am planning on working on this tomorrow so I want to run through some scenarios....

    lets say my fuel pressure is low, whats the next step. Fuel pressure regulator?
     
  4. j cat

    j cat Rockstar 4 Years 1000 Posts

    if the pressure holds at the incorrect psi range with the key on engine off then it would be the fuel pump .

    if the pressure rises then drops fast then this could be anything in the system including the fuel pump.

    then you check psi at the fuel filter if that is good and holds the problem is in the engine fuel delivery. reg/injectors leaks.

    this is with the key on engine off.

    it is possible you have a fuel pump that is going but not gone 100% this is common. may have to drive around with the gage connected to fuel rail and see how it performs.

    engine running it should be around 57 psi. no lower than 53 psi. the engine will run as low as 50 psi but not too good.
     
  5. TimTom64b

    TimTom64b Member 2 Years 500 Posts ROTM Winner Gold Member

    If fuel pressure is good... And have no codes... Then check for adequate spark... Cap, rotor, ignition control module. If all good there could be MAF sensor.

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    One other thing... To reset the codes/ecm you can unplug the battery for ten minutes which would reset everything to defaults.
     
  6. FergusonT

    FergusonT Rockstar 4 Years 100 Posts

    Driving around with the pressure gauge on the fuel rail isn't really an option....the truck wont start.
     
  7. TimTom64b

    TimTom64b Member 2 Years 500 Posts ROTM Winner Gold Member

    You should still.have fuel pressure with the key forward in the run position... As that truck should have an electric fuel pump. Don't really know if you have the fuel pressure guage or not. If not start checking the other things to rule them out.
     
  8. FergusonT

    FergusonT Rockstar 4 Years 100 Posts

    Right. The fuel pump is working with the key on. I just had my wife try the ignition while i tapped on the gas tank, nothing of course. So I am going to run to the parts store and grab a fuel pressure gauge.

    - - - Updated - - -

    I've got enough mechanical ability to repair things, diagnostics is my weak spot. Thanks for helping this far guys.

    - - - Updated - - -

    Ok.....fuel pressure is at around 52psi with key on........
     
  9. j cat

    j cat Rockstar 4 Years 1000 Posts

    driving around with the truck not starting I do agree would be not an option when checking the fuel pressure.

    Since the vehicle does run/start at times most times, this would be the occation to operate the vehicle with the fuel pressure gage on and monitor the pressure for consistant operating pressures.

    This type proceedure is required as some pumps become intermittent.

    - - - Updated - - -

    now that pressure is low but not so low that the engine will not run/start. as I stated before 53 psi to 62 psi is the range spec. KEY ON ENG OFF THE SPEC IS 60-62 PSI.

    What happens is after the engine starts the reg now has a vacuum. this reduces the pressure to about 57psi with a good fuel delivery system.

    NO VACUUM MAX FUEL PRESSURE / MAX VACUUM [engine at idle] REDUCED FUEL PRESSURE.

    you need the MAX for a cold start. after the engine gets going this is then reduced.

    operate the vehicle and see if the pressure stays around the 52 psi. if it drops/increases I would say the pump is the problem because the pump is a motor that will be an intermitent. regulator will always be showing a defect.

    same with injectors or leaks.

    If you replace the pump do not get an airtex pump.

    AC DELCO OR DELPHI . USE VIN TO GET PUMP FOR CORRECT MODULE/PART.
     
  10. FergusonT

    FergusonT Rockstar 4 Years 100 Posts

    yeah I see airtex pumps on all the websites im looking at...thanks for the heads up

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    also, I just pulled the fuel filter, a bunch of black stuff came out of it, thinking its time to do that too anyways
     

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