Earl Selinger
Registered User
So I have an '83 with 6.9, had a similar problem the injector pump was failing and the fuel return check valve was sticking. I would have to remove it and clean it out with a pick and carb cleaner. Had to do this every couple of months (5-10k). It's a small glass ball check valve doesn't take much effort to push the ball in but if it's clogged it can take a while to free it, should be able to look right through the glass ball, if not it needs a good cleaning