Vehicle is a 1992 Dodge B350 van. 5.9L v8, Throttle-Body injected (TBI). 207,000 miles.
The problem is the van stalls out after about 45 minutes of driving. The engine will start to miss here and there, and get progressively worse until it quits altogether. I have a hunch the problem might be electrical, because after the first few misses, the voltage guage takes a slight dip, the a/c does not blow as cold, the lights dim, radio fades out, etc., between the occasional engine misses. Also, if I decreased the electrical load, by turning off the a/c, radio. blower, lights, etc, it seemed to do better, though it still would miss.
Anyway, after the van stalls out, if I wait 5 minutes or so, I can start it again and drive some more. This happened yesterday, when I drove to town about 20 miiles from my house, and headed back. I got to within 5 miles of my house when it started acting up. I made it another 4 miles before it quit entirely, right at the entrance to my neighborhood. I restarted it, and got it the rest of the way home.
It will only do this while driving. I have tried to get the van to fail while idling and occasionally revving in my driveway, and it will just purr like a kitten for hours. It needs to be driven at highway speeds to produce the symptoms.
I guess I might suspect the alternator in a situation like this, but I just put a new stock alternator in this thing two years ago. The battery is a Duralast Gold, put in a year ago. The coil pack, spark plugs, and wires were replaced with stock replacements a year ago.
Anjy suggestions? Thanks.