Here is the latest findings : replaced FPR and retested grounding pin #6 on test plug. 50PSI max pressure. 3 times same result. At idle Pin# 6 not grounded 40PSI. 3 times same results. At idle remove vacuum from FPR 40PSi. One thing I noticed is that when truck is turn off, the fuel pressure drops immediately after engine stops. As compaired to KOEO, pressure holds when Key is off. I am guessing that the External hi pressure pump is failed or is failing. That is fine , I can replace. This still leaves me with the delima of what has caused the intake lift pumps to fail twice in a row????

 

Are you sure your fuel pressure gauge is giving an accurate reading?

 

well it is brand new unit , I can only assume it is correct. I may have another 100psi gage at work. Ill have to check in the am. Why do you ask?

 

Any ideas?
I am probably going to start replacing parts this weekend. The 15 yr old is itching to drive this thing!
Items replaced so far: rear fuel tank,
front and rear tank fuel pump/ sending units ( replaced them twice so far, appear to be bad again ) OEM from Ford Fuel selector valve. Fuel Filter. fuel pump relay, fuel pressure regulator.

Items to replace this weekend: both front and rear fuel pump / sending units, High pressure Pump , and fuel filter.

What I need to figure out: why the front and rear fuel pump sending units have failed twice so far??????

 

You might check the voltage to the pumps. The fuel selector switch at the dash or the Inertia switch have caused low voltage to the pumps.
Of course bad connectors and relays can cause low voltage also.
You need to check the voltage at or near the pumps.

Low voltage will cause high current and that will cause over heating of the pumps winding and burn them out.

 

In the original thread where you helped me test out the entire circuit. I tested power ( with Test Light non LED ) all the way to each pump. I can recheck this weekend with a Digital Volt Meter to see actual voltage.

 

Could this be a bad ground problem? Just throwing it out there, I have no specific experience with your problem.

 

Grounding was an issue I found. PO had cut frame to engine block ground, from neg side of battery. I have since fixed that , But I believe the in tank pumps had already failed.

 

So, perhaps the bad ground caused the pump failure? Perhaps now a new pump will last.

 

I will check all voltages again this weekend. Before I replace parts. and post results. thanks for all the input.

 

OK, so here is the end result this week. Son dropped rear tank and found the fuel pump to be stuck. I am not sure why, bad gas gummed it up, burned up from low fuel level , have no idea. He replaced the pump ( warranty from Auto Supply )
So we are running again. Thanks guys for all the input , thanks to you subford for all of your input.

 

Additional results : last night the son mistakenly filled up the front tank ( still has a suspected bad pump) . When he tried to use the the front tank truck died two times from lack of fuel. This morning on the way to work, we switched to the front tank and drove 30 miles to work no issues. I am thinking the fresh fuel may have loosened up the stuck pump. I know it sounds crazy, but what other explanation can it be?

 

Spectra and Airtex fuel pumps are aftermarket junk.
I've used them both in different vehicles. They always went bad in months.
If you buy one from Ford it will last. But you will need to get a part-time job to pay for it.
I learned the hard way after three went bad. I bought a factory unit. The original lasted
Over 100,000 miles so the new factory part has a while to last.