DTW75

Hello! The boys truck had a leaking front fuel tank so we just replaced it today. He had been running mainly from the rear tank because previous owners stated one of the tanks doesnt run properly. We just bought the truck last week and they told us only the front tank works properly. The boy didnt realize or me it was set to the rear tank the entire time. So, we went ahead and gave the front tank a try because we just swapped it. Well, it bogs very badly, it stalls on us everytime we accelerate. If we switch back to the rear, it runs great. My first thought was, perhaps it was a switching valve for the tanks but this truck only has splitters joining the lines. The switch on the dash only sends power to either pump to run. We swapped the filter for good measure, still the same results.
I was hoping perhaps the front pump was weaker so it may be getting hung up by the filter. Should I assume the problem is the front pump being it stalls out and is not running properly? I cant think of any other reason for this to happen. Both pumps run upon turning the key.

RLXXI

Could be a bad pump in the front tank or someone pinched the lines to keep it from over flowing fuel. Ford had a recall back in the day where in when one tank was used it would send return line fuel to the opposite tank and if it was full. Boom gas spews every where. They actually recalled it twice when I was working at Ford for the same problem.

I performed that recall on hundreds of trucks twice and the problem would always return eventually. Best advice I can offer is use 1 tank only. I don't remember exactly which one had the largest capacity but I think it was the rear tank.
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DTW75

Thank you for the info. It didnt appear the return line from one fed to the other🤔 but perhaps i didnt know to look at the time. At any rate, we will see if it improves, it idles great off of the front pump, its just giving it gas where it seems to want to bog badly. Hopefully, its nothing more than the pump.

Steve83

This diagram & its caption explain how the fuel lines are run:


(phone app link)

The rest of that album explains most of the '90-04 fuel pump system, so keep clicking "NEXT" at the top Left of the page and reading the captions to learn more.

Never assume. The bad pump is the one that RECEIVES fuel from the other (the tank that overflows). And the problem will only get worse if you simply use 1 tank. Either fix & use both, or disable the tank you don't want; either by replacing the fuel lines with those from a single-tank truck with the same wheelbase as yours; or by blocking BOTH the unused lines as this caption explains:


(phone app link)

Modern replacement FDMs don't suffer from the failure that caused the earlier recalls. But most cheap pumps don't last - Spectra & Airtex are the worst. Of course, Ford/MotorCraft is be$t; Bosch might be OK.

The difference in tank capacities is less than 2 gallons at most:


(phone app link)