intermitten low idle misfiring under load

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December 12th, 2012, 5:22 PM

prowe3

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intermitten low idle misfiring under load

I have a 97 Chevy Burban with a 5.7 Vortec. For the last few weeks I have been having an intermittent low idle misfire. Some days it runs perfect. Other days it’s not too bad, and other days it won’t start, or if it does it wants to die pulling off the line. I have gone through many tanks of fuel from different stations with different results every day. I parked it Friday and Monday morning it would not start. I tested the coil. It tested fine. I tested the end of plug #1, it too had spark. So I cranked it, used some starting aid and got it running. Once I got it started, it idled fine but still misfires if you hit the gas hard. If you rev it slowly it revs up fine. I have checked the fuel pressure with the key on and pump running it is at 60psi. With the engine running it is at about 55. When you rev it up it’s about 62 PSI. One hour after shutting it off the pressure drops from 50 to 40PSI. I have been a diesel mechanic for 6 years and this gas engine is kicking my butt. Any help would be much appreciated.
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December 12th, 2012, 6:34 PM

kevinkpk

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Is it throwing a misfire code, and can you "dfeel it"? What rpm is this happening?

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December 12th, 2012, 7:10 PM

prowe3

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Quote:

Originally Posted by kevinkpk

Is it throwing a misfire code, and can you "dfeel it"? What rpm is this happening?

It is not throwing codes. it only does it 800-1500 RPM.

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December 12th, 2012, 7:15 PM

prowe3

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While I was checking the fuel pressure tonight it was missing when I revved it up. I went in ate dinner, then took it for a drive and it ran perfect. it is so intermittent I don't understand it.

PLEASE SOMEBODY HELP!!!!!

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December 12th, 2012, 7:26 PM

kevinkpk

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Quote:

Originally Posted by prowe3

It is not throwing codes. it only does it 800-1500 RPM.

You say low idle misfire, 800 rpm isn't low idle. It is having a misfire at 800-1500 rpm? I'd suspect the throttle body.

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December 12th, 2012, 7:38 PM

prowe3

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It's MPFI

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December 12th, 2012, 8:34 PM

MDTAHOE

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What color is the spark? Blue or yellow? What is the condition of the cap, rotor, wires? What is the coolant temp sensor reading from the computer? Most likely you have a problem poppet style injector problem. Maybe time to upgrade to the new style injectors.

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intermitten low idle misfiring under load

intermitten low idle misfiring under load

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