but again thinking logically - the regulator can close completely and cause the pressure to go up with just the minimal volume for idle requirements - once the volume increases the pump needs to supply VOLUME as well as pressure - I don't think it's a restriction in the line as there is no evidence of crushing, pinching, damage, etc. About the only restriction might be in the in-tank filter sock but if it's like most cars that usually shows up as you get good volume initially and as the sock clogs up with junk the volume drops - when the pump is off the junk drops back down to the bottom of the tank and the sock clears a bit.

SO - It's got to be one of the pumps - which one is the culprit is the question!

PULL THE RELAY OUT FOR THE TANK WHICK U WANT TO TEST

...but what's the chances of something in both tanks, other than crap in the gas, going wrong at the same time?

Well long story short - the culprit - the filter in the selector valve - didn't even know that it was down there - I've replaced the frame mounted fuel filter and checked everything for obstructions, etc. Got the hint from the local dealer that said just to toss the filter as he's seen lots of them plug and cause problems - well, I purchased a replacement (if it's plugging with crap it's got to be doing it's job!) - no wonder why the in-line filter looked perfect - it's getting filtered fuel. Anyhow - now I can run foot to the floor all the way to 70 MPH without bucking or backfire and that's good enough for me!

I want to thank everyone for their help! Didn't have to waste too much $$ fixing it and in the end it was a volume probelm getting to the high pressure pump - just not where I thought it would be!

Chalk up another one for logic. https://www.f150online.com/f150board/smile.gif