My '94 with 5.0 started acting funny a few days ago and it might be getting worse . First I noticed while stopped at red lights and such with the engine running and the truck in drive (I have the 4 speed A/T), the idle would sometimes surge for just one moment causing the truck to surge against the brake. It bugged me but I put off looking into it.
Tonight as I was driving home, I stopped at the light and I noticed a really pronounced dropping of voltage momentarily. The lights would dim and the engine would slow down. Then it picks up again, the lights brighten up, the volt gauge pulses up and the engine pulses against the brake..
When the power drops, the volts drop below the center and when it's running fine, they go up past the center.
I think it does it while I'm driving also, although it's less noticeable. Can some one please help me to diagnose and repair this condition?

Thanks

 

Does anybody have any ideas about this?

Thanks

 

This was happening to me in my 89(especially with a/c on, I had to end up changing the alternator, my buddy had a load tester he hooked up, when he put a load on the battery the alternator couldn't keep up, took 5+ minutes for it to regain it's charge, almost instant now.

So I'd say test the altenator, whether with a load tester or a multimeter with everything on.

 

Thanks! I'll try it. BTW, your truck (in the avatar) looks a lot like mine