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  1. #1

    5.7 vortec sluggish, loss power need help with diagnosis...

    Hey so I need some help on diagnosing this thing.

    I ran out of gas last week. Put gas in ran fine for about 3-4days then just started getting sluggish, loss power, some backfiring when you try to jump on it. so I started with the simple and cheap tricks.

    1. ran about 1/4 tank through with injector cleaner.
    2. replaced fuel filter
    3. tested fuel pressure - steady at 55 at idle, goes up a little with initial pedal, steady then at 55 again, drops with release of pedal, then steady at 55 again. never drops below 50
    4. I have tried 1/2 can seafoam and let it set for about 20 minutes. started it up and idled it up to around 2500 to blow it out. still runs like crap.
    5. trying seafoam again and I am letting it set overnight now.


    but any help would be great.

    thanks!

  2. #2
    Vortec - 55 PSI fuel - Fuel injected right? Check for codes first is the cheapest easy trick.

    I would then check ignition.

    Visually check the easy stuff like cap, rotor, plugs, wires. Check your timing. Make sure the distributor is not seizing up (thus the distributor is turning a bit in the hole). When you have the cap off, grab the distributor shaft and see if it has excessive play side to side.

    It probably was just a coincidence when you ran out of fuel, so I would not assume it was from that.
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  3. #3
    1BADKJ's Avatar
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    Quote Originally Posted by 88chevota View Post
    Hey so I need some help on diagnosing this thing.

    I ran out of gas last week. Put gas in ran fine for about 3-4days then just started getting sluggish, loss power, some backfiring when you try to jump on it. so I started with the simple and cheap tricks.

    1. ran about 1/4 tank through with injector cleaner.
    2. replaced fuel filter
    3. tested fuel pressure - steady at 55 at idle, goes up a little with initial pedal, steady then at 55 again, drops with release of pedal, then steady at 55 again. never drops below 50
    4. I have tried 1/2 can seafoam and let it set for about 20 minutes. started it up and idled it up to around 2500 to blow it out. still runs like crap.
    5. trying seafoam again and I am letting it set overnight now.


    but any help would be great.

    thanks!
    Sounds like a classic fuel pump failure.Just having the correct psi does not mean alot.I replace at least 1 GM pump a week,usually once you run out of gas once they are almost always going to fail soon after.

    Though check the plugs,wires,and cap(if you have one).
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  4. #4
    My codes are:
    P0300 misfire
    P0174 lean fuel
    then a bunch of other non coed stuff that also makes sense since it is running rough.

  5. #5
    Digger's Avatar
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    year and model would be some good info
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  6. #6

  7. #7
    Digger's Avatar
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    key on, engine off, that fuel pump should have 60-65 psi

    5 psi on a vortec is a huge loss

  8. #8
    key on engine off it hits 61 PSI. When I start it, it drops to 53ish. Then sits around 55-58.

    If I have a bad fuel pressure regulator would it cause the fluxuation in the pressure like that?

    If I have a bad fuel pump then can I drop in an aftermarket external and allow it to just pull the fuel through the old one?

    What about the lame injectors?

    It runs rough at idle too. just alot worse under load.

  9. #9
    oh yeah and the seafoam changed nothing other than my wallet.

  10. #10
    trailblazer's Avatar
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    bad fuel psi reg would result in rich codes not lean codes, would check for pluged cat pretty common on this eng with miles. are all missfires on one bank of cyls ? any cyl specific missfire codes po301 p0302 etc. ? have you checked fuel psi when it is acting up ? .
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  11. #11

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    Have you checked the fuel volume spec on the pump?

  12. #12
    Digger's Avatar
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    Subject: 97-05 Vehicles with 4.8 5.3 5.7 and 6.0 Gen III V8 Engines and Misfires on One Bank - kw CEL diagnostics driveability DTC P0171 P0172 P0174 P0175 P0300 P0301 P0302 P0303 P0304 P0305 P0306 P0307 P0308 #PIP3056 - (07/12/2004)

    Models: (00-05 Cadillac Escalade - C6 and K6) and (02-05 Chevrolet Avalanche - C1, C2 K1 and K2) and (99-05 Chevrolet Silverado - C1, C2 K1 and K2) and (00-05 Chevrolet Suburban - C1, C2, K1 and K2) and (00-05 Chevrolet Tahoe - C1 and K1) and (99-05 GMC Sierra C1, C2 K1 and K2) and (00-05 GMC Yukon - C1, C2, K1 and K2) and (03-05 Chevrolet Express G1, G2, G3, H1, H2 ) and (03-05 GMC Savana G1, G2, G3, H1, H2 ) and (04-05 Buick Rainier S1, T1 ) and (03-05 Chevrolet Trail Blazer EXT S1, T1 ) and (03-05 GMC Envoy XL XUV S1, T1 ) and (03-05 Hummer H2) and (04-05 Cadillac CTS-V DB) and (98-02 Chevrolet Camaro FB) and (97-04 Chevrolet Corvette YB) and (98-02 Pontiac Firebird FB) and (04-05 Pontiac GTO VB)

    The following diagnosis might be helpful if the vehicle exhibits the described symptoms.

    Condition/Concern:
    Check Engine Light with a P0300 due to 2 - 4 cylinders misfiring on the same bank of the engine. DTCs P0171, P0172, P0174 or P0175 may also set for the misfiring bank.

    Recommendation/Instructions:
    If the published misfire diagnostic does not isolate the cause, perform the following suggestions as necessary:

    * Perform a fuel injector balance test for all 8 cylinders. If a fuel injector concern exists, it is possible to misfuel an entire bank of the engine, causing multiple cylinders on the same bank to misfire even though the root cause is a single fuel injector.
    * Inspect O2 sensor connections on the misfiring bank for corrosion or water intrusion. If water intrusion is found on the right bank, it may be due to the AC Evaporator Condensation dripping onto the O2 sensor harness. If this condition is found, reposition and shield the harness to prevent a repeat concern and repair the connections.
    * Check for excessive exhaust backpressure using the restricted exhaust diagnosis.
    * Swap the Position 1 O2 sensors side to side to see if the misfires move to the other bank of the engine. If so, replace the O2 sensor.

    Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

  13. #13
    I started it up tonight to move it out of the way and it smelled of gas pretty bad. I guess I'll be checking all the plugs and ignition stuff.

    Digger. my diag tool doesn't tell me which side or pistons are misfiring.

  14. #14
    Digger's Avatar
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    P0174 is the right bank

  15. #15
    I am assuming right bank refers to passenger side. So according to what is listed above Is it possible I have a passenger side clogged cat or bad O2 sensor? What is the norm for exhaust back pressure?

  16. #16
    Quote Originally Posted by trailblazer View Post
    bad fuel psi reg would result in rich codes not lean codes, would check for pluged cat pretty common on this eng with miles. are all missfires on one bank of cyls ? any cyl specific missfire codes po301 p0302 etc. ? have you checked fuel psi when it is acting up ? .
    also fuel PSI holds steady.

  17. #17
    just realized I forgot to mention I can smell fuel while it's running at idle and while I was testing it. no signs of leaks anywhere. I am getting fuel just at the wrong timing.

  18. #18
    trailblazer's Avatar
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    less than 1psi back psi for exhaust. can you check short term fuel trims with your scan tool ? if so what are thay ? bank #1 &bank #2

  19. #19
    changed cap, rotor, plugs, wires. Fixed it! rotor and plugs looked awful. I bought it with 35k on the new motor. I had assumed they had just done a tune up. they definitely had the signs of 40K+ miles on them.

  20. #20
    trailblazer's Avatar
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    nice good to hear.

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