'99 5.3 silverado fuel pressure

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by FergusonT, Dec 16, 2012.

  1. MrShorty

    MrShorty Epic Member 5+ Years 1000 Posts

    Fuel pressure should change a little with engine vacuum. Pressure should be higher with the engine off (no vacuum) than with the engine running (high vacuum). When you give it gas, the fuel pressure should increase (low vacuum) then decrease as the vacuum increases. It might be interesting to hook up a vacuum gauge to see if the fuel pressure changes coincide correctly with the vacuum changes. That said, it really sounds like your fuel system is not keeping up with engine demand -- I can think of no good reason why the fuel pressure should drop off as you goose the engine.

    With a new AC Delco, pump and a new fuel pressure regulator, it seems appropriate to assume those components are functional (though we may want to revisit them if we don't find a better reason). How about voltage to the pump? New pumps that I've seen almost always come with a new wiring harness to "repair" any wiring damage sustained to the harness. Excess resistance in the wiring to the fuel pump could cause the pump to run weak. It might be time to go over the fuel pump circuit very carefully to make sure there are no weak spots in the wiring.

    You did change the fuel filter with the new pump?

    Any sign of damage/plugging/restriction/kinks in the fuel supply line?
  2. FergusonT

    FergusonT Rockstar 4 Years 100 Posts

    All lines look good. I drove it to work today and it is still running bad, starts fine cold, but now SES light is on and blinking. Hopefully I can get to the parts store before they close to get some codes pulled.

    - - - Updated - - -

    Also, yes I replaced the fuel filter.
  3. j cat

    j cat Epic Member 5+ Years 1000 Posts

    since when you rev the engine the pressure drops this tells me you have a restriction on the fuel supply side. I would connect up a hose to the test port and see with the key on how much fuel comes out also if you see debris [black stuff] like you saw before. the regulator has a screen how did that look ?

    as stated when reving the vac drops this is to increase pressure so you lack proper delivery

    the fuel tank could be pinching the fuel lines if not properly run...
  4. FergusonT

    FergusonT Rockstar 4 Years 100 Posts

    the bleed off hose on my pressure gauge is clear, and the fuel looks good, no debris. The old screen on the old regulator was somewhat dirty. The tank looked clean when I pulled the pump. I guess I need to get a better look at all the fuel lines.

    The fact that I can get a good cold start now is encouraging, but I still need to pull the codes. Maybe my gauge is actually off?

    It runs fine cruising on level road, but any acceleration leads to hesitation. Wondering if throughout all of this feeding fuel through the system from testing and turning over, maybe I have a fouled plug or two?

    - - - Updated - - -

    Ok new development, got a code for misfire on cylinder 3
  5. a.graham52

    a.graham52 Rockstar 100 Posts

    flashing SES light means there is a "catalyst damaging missfire" present. how about your basics such as your tune up? how man miles on your vehicle and when was the last time plugs/wires/cap/rotor replaced (i think you sitll hav a cap and rotor)

    heres some info:
  6. FergusonT

    FergusonT Rockstar 4 Years 100 Posts

    No cap/rotor. But it has prolly been a while. I am getting orange spark out of the wire. And I am hearing a ticking noise near the #1 and #3 cylinder spark plugs while its running.

    So I am thinking it is in the clear as far as the fuel pressure problem, gauge must be bad, I need to test it on another vehicle to be sure.

    Plugs are white.
  7. a.graham52

    a.graham52 Rockstar 100 Posts

    hows the plug gap? if you think its been near 100k miles since they have last been changed then its probably time to change them. when its dark out, spray your ignition components (wires coil etc) wit ha mixture of salt water and see if you get any sparking.
  8. FergusonT

    FergusonT Rockstar 4 Years 100 Posts

    Will probably try that tonight. I don't have my manual with me at the moment to see what the gap is supposed to be, but these are Bosch Platinum plugs that have 2 ground electrodes. In my experience with all the plugs I have changed and dealt with, it looks like a large gap. Plugs and wires are on my list this week.
  9. a.graham52

    a.graham52 Rockstar 100 Posts

    are you sure you dont have a distributor or did i read your statement about the cap and rotor wrong?
  10. FergusonT

    FergusonT Rockstar 4 Years 100 Posts

    No distributor as in this truck has coil packs right above the spark plugs. Just drove it home from a christmas gathering and check engine light came on and blinked again. Just hooked it up to my scanner and I got a multiple misfire code.

    Parameter DescriptionResultsDTC for which Freeze Frame was StoredP0300
    Fuel System 1 StatusOpen Loop
    Fuel System 2 StatusOpen Loop
    Calculated LOAD Value1.96 %
    Engine Coolant Temp136.40 °F
    Short Term Fuel Trim - Bank 119.53 %
    Long Term Fuel Trim - Bank 110.94 %
    Short Term Fuel Trim - Bank 29.38 %
    Long Term Fuel Trim - Bank 27.81 %
    Intake Manifold Absolute Pressure10.36 inHg
    Engine RPM581.25 rpm
    Vehicle Speed Sensor0.00 mph
    Air Flow Rate Mass Air Flow Sensor0.74 lb/min
    Absolute Throttle Position0.39 %

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