Socnarftrucks Posted August 21, 2022 Share Posted August 21, 2022 Do I absolutely need the gas going through the fuel tank selector valve?Both low pressure fuel pumps in My 86 F150 with a 302 we’re not working. So I installed a new rear tank pump and completely bypassed the fuel selector valve. The truck idles good ( has a fuel Pressure of 32 PSI but has very poor acceleration and dies off easily. Any help is appreciated. Link to comment Share on other sites More sharing options...
Gary Lewis Posted August 21, 2022 Share Posted August 21, 2022 Does your system look like the one below? And did you just bypass 9B253 or did you also bypass the high pressure pump - 9C407? Link to comment Share on other sites More sharing options...
Socnarftrucks Posted August 21, 2022 Author Share Posted August 21, 2022 Does your system look like the one below? And did you just bypass 9B253 or did you also bypass the high pressure pump - 9C407? Gary: truck is an EFI by the way. I bypassed the 9B253; connected the supply line directly to the high pressure pump. The return line also bypassed it. Fuel selector switch is on the rear tank. Link to comment Share on other sites More sharing options...
Socnarftrucks Posted August 21, 2022 Author Share Posted August 21, 2022 Does your system look like the one below? And did you just bypass 9B253 or did you also bypass the high pressure pump - 9C407? Sorry, yes the system looks like one in the diagram. Link to comment Share on other sites More sharing options...
Gary Lewis Posted August 22, 2022 Share Posted August 22, 2022 Sorry, yes the system looks like one in the diagram. Two thoughts. First, make sure that the high pressure pump is running. Second, the fuel selector valve also has a reservoir on it, and I wonder if it is needed. Hopefully someone else will chime in. Link to comment Share on other sites More sharing options...
Socnarftrucks Posted August 22, 2022 Author Share Posted August 22, 2022 Two thoughts. First, make sure that the high pressure pump is running. Second, the fuel selector valve also has a reservoir on it, and I wonder if it is needed. Hopefully someone else will chime in. The high pressure is definitely working. I am only using the rear tank and the reservoir valve is totally bypassed. I wonder if the reservoir was engineered to provide just the right amount of fuel pressure. Link to comment Share on other sites More sharing options...
Gary Lewis Posted August 22, 2022 Share Posted August 22, 2022 The high pressure is definitely working. I am only using the rear tank and the reservoir valve is totally bypassed. I wonder if the reservoir was engineered to provide just the right amount of fuel pressure. Yes, I'm wondering if the reservoir is needed. Bill? Link to comment Share on other sites More sharing options...
85lebaront2 Posted August 22, 2022 Share Posted August 22, 2022 Yes, I'm wondering if the reservoir is needed. Bill? The reservoir is used even on single tank vehicles like a Bronco. The idea was to provide a place for the high pressure Bosch pump to get fuel from. The pump is very common on EFI Mercedes-Benz cars where it is placed even with or below the bottom of the tank. I am not sure that the high pressure pump can draw fuel from the bottom of a truck tank, up to the top, then in. The only concern I can conceive would be the in tank pump failing from fighting the pressure head. It is designed for the excess delivered to the reservoir to be returned to the tank so the in tank pump is essentially a circulating pump. Link to comment Share on other sites More sharing options...
Gary Lewis Posted August 22, 2022 Share Posted August 22, 2022 The reservoir is used even on single tank vehicles like a Bronco. The idea was to provide a place for the high pressure Bosch pump to get fuel from. The pump is very common on EFI Mercedes-Benz cars where it is placed even with or below the bottom of the tank. I am not sure that the high pressure pump can draw fuel from the bottom of a truck tank, up to the top, then in. The only concern I can conceive would be the in tank pump failing from fighting the pressure head. It is designed for the excess delivered to the reservoir to be returned to the tank so the in tank pump is essentially a circulating pump. Thanks, Bill. So if I understand, you don't see a problem as long as the in-tank pump doesn't fail? Link to comment Share on other sites More sharing options...
85lebaront2 Posted August 23, 2022 Share Posted August 23, 2022 Thanks, Bill. So if I understand, you don't see a problem as long as the in-tank pump doesn't fail? Exactly, if it is a concern, a small relief valve in the line from the tank with it's outlet teed into the return from the engine set just below the max pressure of the in-tank pump (example, in-tank pump 6 psi, relief valve at 4-5 psi). Link to comment Share on other sites More sharing options...
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