We have had this truck for about 1 year and it has been rough starting during rainy weather so we pulled the plugs and replaced them and the wires and it was much better for a day or so and now is so rough running and stalls, back fires etc. so looking at the dist. cap and rotor decided the replace them too and it was good that afternoon for a while but back to ist old tricks now. Yesterday put in a new fuel filter as its used on a farm and not on the road often ( and often low on gas) with not much help. Fuel filter next? Coil? good visiable spark but we have not used a meter yet…thanks!
How about doing a pressure check on the fuel supply?
To a mechanic, “BACKFIRE” means that combustion is coming back through the intake of the engine; that is, it’s FIRING BACK. To everyone else (almost), BACKFIRE means a popping out the exhaust pipe.
If your engine is backfiring through the intake, that means that something in the ignition is crossed, or out of time. Something crossed could be spark plug wires going to the wrong spark plugs; or, the crossing could be taking place inside the part that makes the spark – such as inside the distributor.
If the distributor shaft seal is leaking oil, the oil could be getting into the distributor, causing crossfire. Examine the inside of the distributor for oil. Look in the distributor cap for oil and carbon tracks.
Check the ignition timing. The distributor could be set a little to close to too-high, or too-low timing. Check the centrifugal, and vacuum advance timing within the distributor. For testing purposes, retard the timing (by turning the distributor) a few degrees. Results?
A worn timing chain is another possibility.