1997 Ford F-350 Misfiring

The biggest cause of the problems is the goofball holding the wrench. (Sarcastic smile intended). It sounds like this started out as a simple misfire. You didn't list the mileage so I can't make any judgement calls on the list of possibilities. Spark plugs and wires are the place to start. The Check Engine light should be on, then there will be a diagnostic fault code indicating which cylinder is misfiring. If spark plugs and wires don't solve it, you can swap injectors between the misfiring and one other cylinder, erase the fault code, then see if the misfire moves to the other cylinder.

You created a problem by switching to a higher octane fuel. Too many people think higher octane equals more power, but that is not true. Higher octane fuels allow the engine designers to build an engine that produces more power, that's all. They do that by increasing the compression ratio, then they need the higher octane to prevent spark knock. It's the octane rating that determines how likely the gas is to self-ignite from the heat buildup of compression. (Compression is what ignites diesel fuel). The higher the octane rating, the harder it is to ignite that fuel. If you already have a misfire in one cylinder due to worn spark plugs, you can expect to have more cylinders misfiring after switching to a higher octane gas.

The next problem is turning the distributor. How do you suppose it turned by itself to begin with? If your spark timing is indeed retarded, it is because the camshaft, which drives the distributor, is retarded, and that is due to a jumped timing chain. If the timing chain jumps a tooth or two, the engine will be real hard to start, and when it does, it will have very low power, but it will still run smoothly if all the cylinders are firing. Advancing the distributor will get the spark timing back to where it should be, but that doesn't address the late valve timing. You'll never notice spark timing that is five degrees late. The engine will run very poorly if valve timing is five degrees late.

JUST TO ADD ANOTHER POSSIBILITY

I'VE SEEN THIS HAPPEN ON TWO FORDS, RUNNING FINE ONE MINUTE THEN DOING THE BACKFIRING THING THE NEXT.

AFTER SEARCHING FRANTICALLY AND TRYING TO DO IT METHODICALLY, THINGS JUST WEREN'T PANNING OUT.

NEAR THE END, LINING UP TDC, WE FOUND THE ROTOR BUTTON WAS NOT FACING #1 SPARK PLUG WIRE (HOW COULD THIS BE?)

THE ROLL PIN THRU THE DISTRIBUTOR'S DRIVE GEAR HAD SHEARED.

THERE WAS STILL ENOUGH TIGHTNESS ON THE SHAFT THAT THE GEAR WOULD STILL TURN THE SHAFT/ ROTOR.,.,.,.,.HOWEVER THE ROTOR WAS NO LONGER "TIMED" WITH THE CAM.

WE FIGGERED OUT THE 1st ONE BY FINALLY, TWISTING THE ROTOR BUTTON WITH A LITTLE FIRMNESS WITH OUR FINGERS, IT WOULD DO FULL 360s!

UPON REMOVAL OF THE DISTRIBUTOR, IF YOU JUST EYEBALLED THE GEAR/ PIN, EVERYTHING LOOKED FINE, AS THE 2 ENDS OF THE ROLL PIN WERE STILL IN THE HOLES, IT WAS THE MIDDLE, STILL IN THE SHAFT, THAT YOU COULD NOT SEE WAS NO LONGER ATTACHED TO THE ENDS.

THE SECOND TIME I SAW THIS, AFTER A LESSER AMOUNT OF INVESTIGATION, WE SIMPLY TRIED TO TWIST THE ROTOR WITH OUR FINGERS.,..,.,.,.,.,.,.BINGO!

THIS MAY NOT BE THE ISSUE, BUT IT IS A SIMPLE CHECK, AND NOW YOU SORTA KNOW ABOUT IT!

THE MEDIC