2002 GMC Yukon XL running rough

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by johnlazelle, Oct 4, 2013.

  1. johnlazelle

    johnlazelle New Member

    Our 02 Yukon XL with the 5.3 flex fuel model runs rough at an idle sometimes, then others it idles high and going down the road sometimes it feels like its skipping. The problem is that it doesnt do it all the time, it comes and goes which is making it hard to find the problem. We have 150,000 miles and have done the following:

    replaced fuel filter

    replaced intake gaskets (there appeared to be a leak)

    added fuel injector cleaner (twice)

    My friend who is a mechanic, has a diagnostic tool and he keeps getting alot of misfires from various cylinders, but more misfires seems to be coming from cylinder #2. He also gets a O2 sensor code.

    Any ideas? Thanks to all in advance!

    John

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    I should also note that we put a fuel pressure gauge on and it reads steady at 45-50.

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    spark plugs have about 55,000 on them, wires have only about 20,000 miles on them. We did exhaust manifold last year because some of the bolts were broken.
     
  2. Conlan Rose

    Conlan Rose Rockstar 3 Years 1000 Posts

    That fuel pressure number is low for that truck. Should be in the high 50's at idle.
     
  3. johnlazelle

    johnlazelle New Member

    Do you think it could be the fuel pump or fuel pressure regulator?
     
  4. Conlan Rose

    Conlan Rose Rockstar 3 Years 1000 Posts

    Those are the normal culprits. Fuel pressure regulator is fairly easy to replace so you should try that first.
     
  5. johnlazelle

    johnlazelle New Member

    Just to ad some more info, i took it for a spin this afternoon and the problem gets worse going up a steep mountain road. The engine almost cuts out, bucks and jerks, think i might have whiplash! Just kidding about the whip lash, but you get the idea.
     
  6. Pikey

    Pikey Moderator Staff Member 3 Years ROTM Winner 1000 Posts

    If you pull the vacuum line off of the regulator and fuel comes out then your regulator is bad. It is located on the fuel rail on the top of the motor on the driver side, right around the middle of the fuel rail. You may have to pull the Vortec cover off to get to it.
     
  7. johnlazelle

    johnlazelle New Member

    I pulled off the vacuum line and no gas game out, but i have read that it could still possibly be bad? Am i wasting money by replacing it?

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    So i replaced the fuel pressure regulator and one of the upstream o2 sensors (parts store only had 1) and still have the same problem. The engine seems to run smoother going up hill when i really get after it? I'm really getting frustrated! I don't have money to keep replacing parts and not solving the problem. Any suggestions or recommendations any one???

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    i borrowed a diagnostic code reader and got the following:

    P1639 - 5-VOLT REFERENCE B CIRCUIT FAULT
    P0300 - MULTIPLE CYLINDER MISFIRE
    P0332 - KNOCK SENSOR CIRCUIT LOW BANK 2
    P0452 - EVAPORATIVE EMISSION CONTROL SYSTEM PRESSURE SENSOR LOW INPUT
     

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