I have a '96 Ford F250 Super Cab 4x4 with a 7.5L engine/automatic trans. Milage is 115k.
Recently the engine began to run rough. It began slowly but progressed to the point now that it won't even idle when warm. The problem exists throughout the RPM range although it appears to smooth out some right before it shifts into a higher gear.
I suspected worn out plugs and relaced the plugs, wires, and the distributor cap and rotor. The problem remained.
Additionally, the Check Engine light is NOT on. Other things looked at include a visual inspection of the vacuum lines which appeared serviceable and I also pulled the plug wires one at a time to see if there was a dead cylinder with no noticeable results. I don't think it's a fuel problem as there is some popping from the exhaust indicative of raw fuel being dumped into it and there is also a fuel-rich smell to it.
An inspection of the new rotor revealed that only about half the contact blade shows any sign of wear. I suspect that the ignition is only firing half as long as it should and this is insuffcient to reliably ignite the fuel-air charge.
I'm thinking that either this is a sign of my coil failing or the pick-up coil in the distrubtor is failing. However, before I go shotgun-troubleshooting, I would like to know if I'm on the right track or if there's anything I've overlooked?
I replaced the coil. When I looked at the electrode closer I noticed that it was badly pitted and corroded (see pic). I thought for sure I had found the problem. Unfortunately the issue still remains.
I'll be replacing the distributor next (rather than go through the hassle of completely disassembling the current distributor just to replace the pick-up coil. It's only $25 more for the whole assembly).
If that doesn't work, I'm out of ideas. Any suggestions?