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'02 Suburban dies under load / power

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by kbroderick, Jun 2, 2010.

  1. kbroderick

    kbroderick New Member

    I've got a 2002 Suburban with about 140k on it. It's taken to an obnoxious habit of dieing under load (i.e. when going uphill or attempting to accelerate). I brought it to the shop across the street to pull the codes, and it was apparently reporting an O2 sensor fault, but the mechanic felt that the fuel filter was a more likely issue and did that first. When the Check Engine light initially came on, I noticed that the truck was down on power (particularly when attempting to pass vehicles doing 5-10 MPH under on a 50-MPH, two-lane state highway), but it didn't start the cutting-out dance immediately. I drove it with the light for a few weeks (probably about 600-700 miles), as this has been a company vehicle and the guy who could authorize spending money to fix the problem was on vacation.

    Since then, the Check Engine light has stayed off, and the problem with the engine cutting out got better for a while (maybe 300-400 miles?) and is now worse again. I can generally recreate the problem by getting hard on the accelerator while going uphill, although the truck will rev through most of the range without a problem if not in gear. I had been able to deal with driving the truck by keeping my foot a little lighter and trying to keep the revs below 3500-3700, even when accelerating, but now even moderate load increases are stalling out the truck.

    Many of these symptoms seem to overlap with those reported in the "single mom, please help" thread, but some don't (particularly the O2 codes). This is feeling more and more like a fuel pump issue to me, but shouldn't the computer be throwing fuel system-related codes?

    Also, if the fuel pump is the culprit, should I see fuel pressure issues even without a load on the engine? I do have a fuel pressure gauge and could try that, but doing so while moving seems difficult.

    Thanks,
    Kevin
  2. ecombe

    ecombe New Member

    Kevin,

    Don't want to repeat the entire story, since you read the singlemom thread, but it sure sounds like the fuel pump. I suppose insufficient fuel from the fuel pump could cause a number of other fuel/exhaust issues. Might explain why your O2 codes are showing or maybe it is time for a new O2 sensor - in addition to a fuel pump. Either way, I hope you get it resolved. Good Luck.
  3. DTACA Burban

    DTACA Burban Member

    Check your exhaust manifolds. Make sure ALL of the bolts are there and no bolt heads are broke off. If even one is broke (could be hard to see) it could throw an O2 sensor code due to air being sucked in at the manifold/ head. This could be why it only happens under acceleration. I had a similar problem with my '02 and it wasn't until a couple bolt heads broke that I was able to pinpoint the cause.
  4. MrShorty

    MrShorty Epic Member Staff Member 5+ Years 1000 Posts

    He didn't happen to tell you which O2 sensor code, did he?

    O2 sensor codes can easily be caused by fuel system issues. O2 sensor is part of a feedback loop that regulates fuel mixture (o2 sensor reports lean or rich to PCM, PCM adjusts injector pulse width to get the right mixture). A problem in fuel delivery easily interferes with this feedback loop, which triggers the O2 sensor code. I guess what I'm trying to say is that an O2 sensor code is (potentially) a fuel system code.

    Hopefully you'll see a fuel pressure issue without a load on the engine, because that makes it easier to diagnose. However, I wouldn't say that you should or shouldn't. If you don't see a problem with no load on the engine, the only way to for sure eliminate fuel delivery as the cause of the problem is to test it with a load on the engine.
  5. kbroderick

    kbroderick New Member

    Thanks for the suggestions. I'm going to plan on putting a fuel pressure gauge on the system and seeing if I can verify that the fuel pump is not working correctly, and I'll try to remember to check back in here to get the resolution (once there is one) in the thread.
  6. kbroderick

    kbroderick New Member

    Just digging through my old emails to clean out the inbox and realized I never posted that yes, it was the fuel pump.

    However, it was providing good fuel pressure at idle; it was only under load that the fuel pressure would drop. The shop apparently didn't have a scanner that would provide live data during operation, but once they borrowed one they were able to see this. So far, no trouble with a new fuel pump (although I've also put a lot more miles on the bike than the truck this summer, so I am hoping that the problem continues to appear resolved through the winter).
  7. kbroderick

    kbroderick New Member

    So as yet another follow-up, the TPS was also bad. The truck sat for a while (my primary summer transportation is two-wheeled), and ran fine on the first trip out this fall. Then, it started hesitating and seriously lacking power (although it would run fine with a very light touch on the throttle and a willigness to pretend it was a 250cc motorcycle engine, making hills a bit tough). Took it back to the shop; the new fuel pump was not putting out sufficient pressure, nor was the TPS functioning correctly.

    It seems okay now, hopefully it stays that way.

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