Sorry to reply to my own post...
It was a fuse. I just checked them all until I found a failed one. After replacing it, went back and they got a 402 - EGR Flow Excessive. Surely this fuse couldn't be for the whole PCM - it wouldn't run at all would it?
Anyway, the EGR valve checks OK. I took it off, cleaned it and tested it with a vacuum pump. When closed, it seems to seal well.
I hooked a vacuum gauge to the EGR side of the vacuum solenoid. No vacuum at idle, vacuum at mid throttle, none at higher throttle (this is with the van in Park and warm).
All of this seems to be correct. Am I missing something?
TIA, Wallace
The "Service Engine Soon" light on my 1997 Econoline 150 4.2L has been
> coming on for hours/days and then going off.
>
> I've gone to AutoZone twice (when the light was on) and they don't get
> any output codes (the scanner does not come on).
>
> I don't have the owner's manual, and I was wondering if it might be a
> fuse? There is also no lights on/key in ignition chime - maybe the
> same fuse, or maybe it just doesn't have one?
>
> Any insights?
>
> TIA,
> Wallace