1996 F-350 starts but runs rough

[steelheader]

When I went out to start my truck today, I unplugged the block heater, it's kind of cold here, started it and began to wait for it to warm up for a few seconds. All of a sudden it just started to idle really, really rough. I took my wife's truck to work and tonight when I got home I replaced the fuel filter as I suspected that as the problem. It still idles terrible but had a minute or two of smoothing out then settles back into the really rough idle. When I raise the engine speed up to 1 to 1 1/2 grand the interior lights seem to pulse as if there was a blinker on or something like that. After the few minutes I idled it hoping it was just bad fuel it needed to work through I shut it off and happened to feel the alternator before I closed the hood. It was very warm and I don't think anything really had enough time to warm up that much (the exhaust had not). Could this be a faulty alternator? I hadn't plugged in the block heater all year up until now. Could it have fried the alternator or some other electronic component? Thanks for any information you might have. OOOOps! I left out some important information! When it runs rough it shows the check engine light and it is a diesel Powerstroke engine. Thanks again!

[alaska_psd]

It sounds like your glow plug relay is staying on. Once you have the truck running disconnect the relay and see if the electrical stops pulseating. If it dose Napa has them for about 20 dollars.

[ModMech]

The block heater was coincidental, and did not cause the problem.

The fact that the alternator was warm does indicate that it is working much harder than it should. The first thing to do is to see why (check system voltage both engine off and on).

Next have any codes read, your local AutoZone will do this for free.

Two other possibilities are the cam sensor, or the injector drive module (I hope it's not this). Usually when the cam sensors die, the engine will not run at all, or even start, so this should not be the problem. The injector drive module CAN and does cause the problems you describe, but the misfire is obvious and severe (like it's running on 4 cylinders not 8).

[steelheader]

I smelled some burned insulation when I checked my oil so I pulled the valve cover off and see that I have a burned undervalve cover harness. Thanks for your help. That might have been the cheapest thing it could be anyway! Thanks Again

[jamfu]

while your at it, check to make sure you have the proper vacuum. you can get a gauge for 30 bucks, and it can tell you a lot. you may have weak valve springs.

[ModMech]

A vacuum gauge on a diesel is worthless, they do not have a throttle plate.