Help, this currently has me befuddled. I have an '04 F250 that is surging rythmicly. The Idle RPM seems to hold steady for the most part but it sounds as if the load on the motor is going up and down, up and down. It also has my head lights going bright then dim, bright the dim. I also get a flickering battery light that keeps time with the surging. The pace of the surging seems to get faster with more load on the motor. This usually has little effect on the motor but things get worse when it is cold out. Any one have any ideas?

 

It almost sounds like your alternator output is surging. It would be an interesting test to put a voltmeter one of the batteries while this is happening.

 

Yes the system voltage seems to be going up and down, but I have not had a meter on it yet to see the high and low numbers. Any way I could tell if this is the alternator output dropping, or a load somewhere in the system loading things down?

 

I doubt it's load related, unless it's a really screwed up Glow Plug Control Module. That's about the only thing that I can think of that would put enough load on the electrical system to be that noticeable. You could unplug the GPCM and see if it goes away, that would eliminate that problem.

If it is related to the alternator, I would more suspect a really screwed up voltage regulator.

 

Thanks for the input. Any other opinions on this would be appreciated as well.