I'd check for a leak somewhere. Replacing the external pump with no increase in pressure would tell me either a blockage or a leaks elsewhere , or a low current feed to the external pump. Have you checked voltage at the pump?

 

I know a real good and reasonable, sort of old school mechanic just a few miles to your east in Dawsonville. He does all the work on my truck.

 

Oh yea, that was the other thing! The plug-in for the external pump was corroded up inside where you couldn't see it. Cut it off and wired it together and that solved that problem.

 

I'm very interested to know what the outcome of your problem is seeing how I am having the exact same problem. I also replaced my inline pump but still no change. It's like my motor just isn't getting fuel and I can't seem to trace down the problem.

 

As I said before, check that canister for a filter, if your truck has one, that is.

 

et_miller_87 nailed it and so did eakermeld. My tank selector switch had shorted, melted and fried. It looked good at a glance but I would have seen the damage had I spent more time there and not had tunnel vision on the fuel pump. That short at the switch shorted out quite a bit of other things as well. et_miller_87---I will start learning about the electrical. You were right about low current. eakermeld--the mechanic said if the electrical had not got me, the cannister would have. Thank you all very much for your guidance.

 

No prob man. Glad we helped you get your truck back on the road

 

Who do you use? I'm in Dawsonville as well. I usually use Mullinax in Dahlonega for the stuff I don't want to do.

 

So it was the actual selector switch that was shorted? My 351 runs fine until you need to accelerate or go up a hill, then it sputters and occasionally backfires thru the intake. I tested the fuel pressure at the rail and it was within specs. I'm about ready to throw in the towel til spring. Any advice is appreciated.

 

Grantslicker, something to look into,as a general rule, check for codes first. Even if the CEL isn't on, there might be codes in CM. Another direction to go is to check all the vacuum lines, check the spark plugs for a bright blue, healthy hot spark. And just because you've got good fuel pressure doesn't mean you don't have a fuel delivery problem. Clogged injectors could be a culprit in some cases.

 

Rig up the gauge so it sticks out of the hood then take it for a drive and see what the pressure does. My 89 tested fine in the driveway but did that same thing out on the road. At least you will know.

 

So what kind of psi should I maintain under load? Or should I ask what kind of drop did you see?
So your selector valve was the problem?

 

35psi at idle, 45psi at WOT. There was a filter in the valve that wasn't supposed to be there. It was plugged up. That was the new, one year old one. The original valve was letting fuel pass between tanks. After I replaced it I took it apart and found some gunk under one valve. Be VERY CAREFUL removing that bowl from the selector valve. You cannot buy replacement parts like o-rings and such.

 

Thanks for the info, now if I could get some nice weather. Lol. Those camper mirrors are too damn wide to fit in my wife's garages.

 

Well, I did a fuel pressure test today, my results were:
Engine off 38 psi. (Ok)
Engine idle 33 psi (ok)
Engine idle vacuum disconnected from FPR 42 psi (ok)
Turn off engine and at 1 minute pressure drops to 20 psi (failed). It didn't take long to drop to zero. I also noticed a small amount of fuel in the vac line.
I'm in the process of removing the FPR, what a PITA that job is! Basically have to remove the fuel rail. I sure hope this makes a difference.