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Backfiring 502 EFI

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Old 06-21-2010, 01:47 PM
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Default Backfiring 502 EFI

My motors were pulled last year. After re installation one backfires around 2500 - 3500 RPM. I have replaced the throttle position indicator, checked firing order, checked for codes (none), swapped MAP sensors. Compression check is next. Can anybody think of anything else?
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Old 06-21-2010, 01:50 PM
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Check fuel pressure when it does it, backfiring can be due to lean mixture.
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Old 06-21-2010, 01:57 PM
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Thanks for the input, I seem to recall that the fuel pressure was OK but I will double check. I don't think its fuel related though because it runs fine WOT.
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Old 06-21-2010, 02:10 PM
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Have you got a good cap, rotor, and plug wires on them? At 2500-3500 you are pulling "over the hump" so any lean condition or loss/scatter of spark will be magnified at that point.
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Old 06-21-2010, 02:37 PM
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Pull the cap and lock tite the rotor. should fix the problem
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Old 06-21-2010, 04:02 PM
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Thanks, I will try that and let you know.
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Old 09-14-2010, 05:05 PM
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Problem turned out to be the fuel pump and pressure regulator. They were both working well enough to run great at idle & WOT, but not well enough to run when the load got high either coming up on plane or when I backed off a little. Which seems to indicate that the best fuel economy is somewhere over 40 MPH.
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Old 09-14-2010, 10:49 PM
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My 502 efi developed shutting off this past weekend @ 4000 rpm.... I could run 3900 all day, as soon as I hit 4g's It would shut off... If I backed out fast enough & pumped the throttle about halfway I could save it from stalling sometimes, fuel related? But any ideas where to begin?
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Old 09-15-2010, 05:04 AM
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fuel pressure problem for sure. had the same issues about a month ago...
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