My stepdad is trying to figure out what is going on with an f-150 he is trying to get running, but cant figure it out.

The truck will NOT start, and while cranking, the engine backfires thru both the exhaust and intake. He has replaced the spark plugs, wires (ford wires) cam sensor, and he told me the crank sensor also??

Does anyone have any ideas what might be going on?

I went and listened to him try to start the truck today, and the truck sounds possessed...

Supposedly the last time it was filled up, it was filled up with diesel, and then driven until it stopped running, but i do not know for sure if it was actually running before that point or not.

Thanks.

 

Is there diesel fuel still in the system (verify by checking at the test point on the fuel rail while running the fuel pump)? If there is, drain and purge the system all the way to the fuel rail.

Check engine compression with a screw-in gauge (after removing the fuel pump relay and disconnecting power to the ignition coil!).

I'd give it a fat shot of starting fluid or Gumout down the intake (hold open the butterfly) then try cranking it. Engines will usually run for a few seconds this way even if the fuel system has problems. If it does not I'd suspect mechanical problems, but would try this several times.