after running great for a hour or so starts back firing and knocking. won't run not over heating, pull over for 30-60 minutes runs great again


Asked by Jun 19, 2013 at 09:01 PM about the 1991 Ford F-150 XL 4WD Extended Cab SB

Question type: Maintenance & Repair

got two gas tanks. fuel pumps in both, no booster pump try to swicth tank, when it happens no luck so don't think its the fuel pumps, try a new fuel pump relay. new computer relay. should i try a new  ecm computer, got three codes code 33 insufficient e g r flow, was told that would not cause the problem. code 62  and 65 trany codes, don't thing the traney would cause it.truck runs great for a hour or so than starts back firing and knocning. pull over 30-60 minutes run great not over heating. can anyone tell me what i should try and in what order thanks Howie

4 Answers


Backfiring sounds like ignition problems, have you replaced the distributor pickup and module?

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Tracy Hooks

That's the first place I would look too. Check for spark as soon as it dies. The electronics fail in the module because of the 99% duty cycle. An ignition coil can cause these troubles too but usually a coil fails and stays failed.

1 out of 1 people think this is helpful.

try laying a bag of ice on the computer when this happens. [if the computer is heating up] this should correct what's happening. will tell you if you have to replace the computer

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Had the exact problem with a hopped up early 70's grand torino sport. "I'm not quite as old as Clint Eastwood" but not far away either." Would run absolutely teriffic for about half an hour, then dead. Cool off, would run great then die again. Old mechanic stated the power pack was going bad. Suggested next time it dies, dumb cold water over the pack to cool it off. WORKED. Had to reroute the power pack from the side firewall fender well to a location closer to the front near the radiator to keep it cool. Sounds like you have a problem with an electronic part overheading then sending incorrect signals.

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