390 problems

[Sean68f100]

I have a 68 f100 with a 390 that just started randomly shutting off when driving then backfires and continues to run fine. Sometimes it will backfire a few times and shut off but then runs perfect. It only does it randomly and it’s driving me insane I can’t figure it out. Any help is greatly appreciated.

[BobbyFord]

Sounds like your ignition is intermittently losing power. Bad switch, loose or broken wire...check coil power wire, wire going from coil to points...

[idaho_cowboy]

Bad cam timing gear.

[Ohiotinkerer]

When I got mine did a full tune up on it but was noticing the same symptoms just not quite as bad as you are experiencing - put a new timing set in and cleared right up.......check that along with what BobbyFord suggested.......

[sargentrs]

Take your distributor cap off and watch your rotor while you turn the engine over by hand. You can put a socket on the crank boltt or might be able to do it with the fan. You only need to move it a little back and forth a couple of degrees. You're looking to see how far you have to turn the crank before the rotor moves. More than a degree or two is an indication of a loose/sloppy timing chain.

[bluef250]

check the play in distributor shaft also

[tsherry]

That sounds like the problems I was having with my 351W in my Galaxie. Turned out there was crap in the oil pump that caused the distributor drive gear shear pin to give way...but it would work for awhile, obviously getting some traction on the remains of the drive gear, and then quit again. (distributor quit turning). Pulled the distributor, replaced the pin, replaced the oil pump and solved the problem.

[Gray035]

I was experiencing similar symptoms. For me it was a bad module in the distributor in my Unilite electronic ignition system. Whatever is going on it sounds like something in the ignition system to me.