1997 Chevy 5.7L Vortec backfiring rough idle

Discussion in 'Chevy Truck Forum' started by green4x42003, Oct 29, 2015.

  1. green4x42003

    green4x42003 Full Member

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    Hello, I have a 97 K1500 with a 5.7. I am at a loss for an issue that arose today upon a heavy acceleration this occurred out of nowhere and now will not go away. Rough idle almost like a miss at idle, upon acceleration out backfires through the exhaust. The two codes that were thrown when this problem began were an intermittent P0175 (fuel trim system rich bank two) and a non intermittent P0420 (catalyst system low efficiency bank 1). The truck runs horrible and backfires severely under load.any help would be a blessing.
     
  2. f150fan

    f150fan Full Member

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    How many miles are on the motor? Sounds like timing issue, get a light and check the timing.chances are the chain is worn its a little out of time with may cause it to throw the codes
     
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  3. chevychase

    chevychase Semi-Admin
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    This is a hard code to diagnose po175..the truck is running rich ..po175 means the passenger side 02 sensor is reading a rich condition.
    Must be real rich..cause you got the po420..if you keep running it this way you will ruin the catalyst system/converters.
    Could be a lot of things cause this..coolant temp sensor...fuel regulator...injector stuck open...real dirty maf sensor..etc. etc...you have a misfire...bad plugs...wires...distributor cap
    could be bad..anything wrong..the pcm/computer may add fuel..to compensate for the condition. We know it is not a vacuum leak..would be opposite..get other codes.
    Even if thermostat is stuck open might cause this? You will waste money..and parts..need a good scanner/garage to look at fuel trims etc.
    Could clean the maf sensor...check the coolant temp sensor...check fuel pressure etc..i will leave some links how too...oh take a look at dist. cap .
     
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  4. green4x42003

    green4x42003 Full Member

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    It's high millage, 290,00. There was no noise when the problem occurred and sill no noise. It wasn't a problem that developed slowly, it was in an instant under a heavy acceleration.
     
  5. green4x42003

    green4x42003 Full Member

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    No misfire. not driving the truck. Cats are hollow. New plugs and wires. Fuel pressure is good at idle and under load. Replaced the cam sensor. cleaned the maf sensor. Problem persists
     
  6. chevychase

    chevychase Semi-Admin
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    In this link will tell you how to check maf..and clean the maf..how to check for misfire..and others..fuel pressure also a great diagnostic link ..click link.

     
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  7. green4x42003

    green4x42003 Full Member

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    No misfire. not driving the truck. Cats are hollow. New plugs and wires. Fuel pressure is good at idle and under load. Replaced the cam sensor. cleaned the maf sensor. Problem persists. Cap contacts have slight white but again, no misfire code and misfire monitors ok
     
  8. chevychase

    chevychase Semi-Admin
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    If it was a sensor cam..crank.. etc..you will get a code for these..except the coolant sensor will not most times.
    Also high miles..heavy acceleration..might check compression? If it was a cam..or crank sensor would not start deal..coolant sensor beside the thermostat housing little 2 wire sensor.
    Does the fuel pressure hold when you turn truck off..you can just turn key to on to check fuel pressure..like said a hard 1 to diagnose po175..po172..and lean codes also.
     
  9. f150fan

    f150fan Full Member

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    290k miles is a lot of miles I'm still thinking timing,you can lliterally spend a1000 or more guessing dignastic is hard but the key here
     
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  10. green4x42003

    green4x42003 Full Member

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    So if I take the timing route, do you suggest I check the distributor gear or the timing chain and sprockets first?
     

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