back firing under load


Asked by Jun 27, 2013 at 08:23 PM about the 1995 Ford F-350 2 Dr XL Extended Cab LB

Question type: Maintenance & Repair

I have a mtorhome made by thor using a ford big block I have a back fire issue when under load like going up hill I have check plugs, wires, timming, fuel filter, it almost feels like a governer on it didnt always do this idels great I need help on what to look for

9 Answers

going to have to suspect an EGR valve full of carbon...take it off and spray it with brake cleaner or buy another one~

2 out of 2 people think this is helpful.

I'd recommend a complete tune up first. Replace cap, rotor, wires, and spark plugs. Be sure spark plugs are gapped correctly. As The Judge said clean your EGR valve too. Also check that your ignition coil isn't breaking down as well. HTH. -Jim

2 out of 2 people think this is helpful.

under load, Jim? a romantic thought to condemn the ignition...sad the EGR is not working correctly....touchy technology at the outset...add use and carbon becomes tough to get any answers out of this criminal~...a nice Idea, to "cool down" the combustion with it's own exhaust, but when not doin' it right makes waste of an otherwise perfectly good motor~

1 out of 1 people think this is helpful.

the onboard diagnostics will have something to report...get the diagnostic info please....get your own OBD-II scanner...this might help to pinpoint the culprit~


Hi Judge, I've had ignition systems perform fine but as soon as you step into the gas pedal they break down. Another cause of backfiring, although probably not the case here, is a bad diverter valve for the A.I.R. system. This will cause a VERY loud, gunshot type, backfire out the tail pipe when you let off the accelerator or shut the vehicle off. I had a car once that was backfiring out the carburetor under load. Found two spark plug wires had been swapped when a tune up was done. Fixed the plug wires, problem solved. HTH. -Jim

1 out of 1 people think this is helpful.

wow. Jim, thought for sure this had a troublesome TPS that would send errant signals to the ECU causin' the backfire but sounds like yours doesn't have one, but the ole' fashion cable type throttle?---my bad~

the report would wring-up a TPS (maybe) as this being the only connection between you and the computer will see a lot of use and hopefully took the time to make it an optical device rather than a "feather weight" these prices would be kind of a fool to NOT go for it, even if this WEAR item isn't worn yet~


Sorry to bother you guys but has he checked his fuel pressure? and is this an actual BACKFIRE? I get these descriptions sometimes and go drive it and find it is better described a little different. Have replaced loads of egr valves, but never a thermactor diverter. Lots of exhaust check valves though. I know, I know- must see to appreciate. hope a few other ideas help.

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