PO171 and 174

by flynlow22 on Jun 28 2017, 2:04 PM

I'm having some problems with this one. This is my personal truck, it is a 2004 GMC Sierra 1500, 5.3, VIN T. This issue only happens in 100 + degree weather when pulling a hill. The water temperature is normal and all other parameters are normal then all of a sudden the long term fuel trim starts climbing to 20% plus, the truck looses power, then ultimately stops running. The codes that are present when this occurs are PO171, PO174, and PO300. If I open the hood and let things cool for 15 - 20 minutes, the truck will normally start and run fine. This problem has been going on for two summers. Over that period of time I have replaced the fuel pump, mass airflow sensor, intake manifold gaskets, map sensor and throttle body. I have thoroughly checked for vacuum leaks, checked the air intake after the MAF, and disconnected the power brake booster, all with no change whatsoever, in fact, the problem is getting worse. Any input would be greatly appreciated. 

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13 Replies
  • By vazquez audi & vw
    I would do a smoke check and also a fuel pressure test, the intake gasket is a common failure in this truck is pretty common. I will check fuel pressure first and then do a smoke test if this checks out to specs 
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  • By 1986chevyman
    I would  be checking for a bad connection at the fuel pump
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  • By captain obvious

    my first post in these forums, so bear with me please.

     

     you're getting the lean codes first. these are happening due to the ecm pulling fuel, or a restricted fuel supply. this is in turn causing the random misfire code.  it looks like you've covered most of the more common poss. causes already, but i found a tsb for an updated fuel pump for high elevation/high temps(above 80F) check tsb #05-06-04-046A. is that the one you installed?

     

    hope this helps!

     

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  • By captain obvious

    my first post in these forums, so bear with me please.

     

     you're getting the lean codes first. these are happening due to the ecm pulling fuel, or a restricted fuel supply. this is in turn causing the random misfire code.  it looks like you've covered most of the more common poss. causes already, but i found a tsb for an updated fuel pump for high elevation/high temps(above 80F) check tsb #05-06-04-046A. is that the one you installed?

     

    hope this helps!

     

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  • By hotrodjd
    If you have a mass air flow on that vehicle ? Be sure to clean it and inspect well.
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  • By dustyviper340
    If both oxygen sensors read normal until a heavy load ( pulling a hill ), then drop to almost zero or hit zero I would definitely be looking into a fuel starvation issue. Don't forget about possible restricted exhaust either, hit the cats with a rubber mallet listen for rattles... Just a couple Ideas to think on! 
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  • By adam gross
    This will be my first post anywhere on this forum.  I see lots of good info so far.  I had similar issues with mine some tears ago.  Ended up changing both front O2 sensors.  I don't usually suggest throwing parts at at a problem but assuming the plugs are good and no exhaust leaks I  think i would be a good start
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  • By mattperins
    Well, sitting at a desk here in Texas, it sounds like you may have a lean misfire. I would start by looking for known issues like a broken exhaust stud at the manifold. I would also look at ethanol content in your fuel. This has been an issue were seeing more often and you can get a kit that will measure the content. Older vehicles are especially susceptible to ethanol, as theres no strategy built into the PCM software to account for it. If youre not running AC Delco plugs, put those in as well. Check these three things first and get back to us.
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  • By chaz_bentley
    definately is going to be a misfire
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  • By jeffreyd1
    If your truck is a flex fuel vehicle, be sure to look for the alcohol content of the fuel. From time to time we see that cause fuel trim problems. If not a gas/ethanol 5.3 then this will not apply. Most scan tools will be able to give you this reading.
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