engine swap or replace

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Oct 10, 2021 | 08:13 AM

#16

rla2005

Fleet Owner

Joined: Oct 2005

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From: Kentucky

Fuel system diagram for 1990 and later gas engine F-Series trucks w/dual tanks

Attachment 277308

Each tank has it's own Fuel Delivery Module (FDM)

Oct 10, 2021 | 09:38 AM

#17

Edgethis

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From: Tobyhanma, PA

Thats pretty nifty. Didn't know they had that. Makes sense, in case one pump fails you can still drive off the other tank.

Are the check valve not replaceable by themselves? But if you have to pull the tank or bed might be worth replacing the pump as suggested one at least one. Then maybe add a check valve or ball valve shot off on the other line to prevent bleed off.

Oct 10, 2021 | 09:59 AM

#18

coneheads

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Quote:

Originally Posted by Scndsin

At key turned to "on" but not to "crank", selected pump should run (audibly) for 1-2 seconds then stop. If pumps run continuously, there is a problem with computer.

It will produce enough pressure on the injector rail for the engine to start & run at which time the same signal that fires the ignition will "tell" the computer to keep the pump running.

Any sort of wait period between what you're doing & the truck actually running, is coincidence & taking you away from actual problem.

That's the problem there is no pressure in the fuel rail the truck will not run until it reaches pressure and shuts off the fuel pump. After that it runs normally regardless of which tank is selected, I hear both fuel pumps running strongly when they are selected. No matter which tank is selected the same thing happens, the pump must be turned on and the truck will not start until it reaches pressure. Which is what leads me to believe that it is something inline and common to both tanks, it seems unlikely that both fuel pumps would have the same failure at the same time, not impossible but unlikely.

Oct 10, 2021 | 10:07 AM

#19

coneheads

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Quote:

Originally Posted by Edgethis

Did the gas trucks not have a tank selector valve? I have one one my 96 as do all the other dual tank trucks I thought, at least the diesels.

That sounds like what the OP is describing. They're not cheap to replace properly, about 500. Alot of folks just eliminate it and run a single tank. Bronco tank is cheap and easy to swap in with a good capacity.

It does indeed have the tank selector switch which is functioning but the symptoms are the same regardless of which tank is selected, but the more responses I read here I think perhaps I have fooled myself into believing it is more complicated than it is. This site is great!

Oct 10, 2021 | 10:13 AM

#20

coneheads

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Quote:

Originally Posted by My4Fordtrucks

I’m saying your truck does not have a dual function reservoir on the frame rail. Each in-tank high pressure pump has check valves in the fuel pump module to prevent fuel from flowing into the wrong tank. I’m no expert but to me it sounds like you have a problem with the fuel pump or pumps so you are not building pressure.

Looking at the diagram that RLA very generously posted and upon further thought I believe it may be just the front module that has failed., The fuel is sent from the back to the front never the other way around, and the fuel level indicator does not work in the front tank either though that is probably unrelated to the fuel delivery issue. I'm going to order one and replace the front one and see if that fixes the issue, if not I can always order a second one. Thx again

Oct 10, 2021 | 10:19 AM

#21

coneheads

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Quote:

Originally Posted by torq'ta 5 8

Cant use any of it, its OBDII, and you will need the OBDI harness, and PCM

Got it scratch that off the list, I have also checked out other post's that actually did it including switching out the harness computer etc but came to regret it LOL overly complicated and expensive requiring custom wiring harnesses, no thanks.
Thx for your input

Oct 10, 2021 | 10:26 AM

#22

coneheads

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Thanks for taking the time to post the diagram it did help me understand the system better. I think I have narrowed the issue to the front fuel pump assembly, the fuel only goes from the back tank to the front and never the other way around. I am surprised that the system ever reaches pressure but I think I fooled myself into believing it was more complicated than it is.

Oct 10, 2021 | 03:12 PM

#23

rla2005

Fleet Owner

Joined: Oct 2005

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From: Kentucky

Just to confirm the fuel pump turn on cycle....when you cycle the key from the Off to Run position the pump stays on for ~20 minutes?

If that is correct you have a bad computer (PCM). Classic symptom on these trucks.

There is no pressure sensor to tell the computer to shutoff, it's strictly a pre-programmed timer in the program code. It is supposed to be about one second.

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Oct 10, 2021 | 04:02 PM

#24

Conanski

FTE Legend

Joined: Jun 2006

Posts: 31,930

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From: Ottawa, Ontario

Then whole FDM module is classified as "non servicable" by Ford, but that isn't entirely true as I have diassembled these before and replaced the fuel pump. I have also disassembled the check/shuttle valves but IIRC it required breaking them apart which means they really are not servicable. If you have the fuel crossflow problem between tanks the FDM should be replaced.

As for putting the Explorer motor in your truck, the way to do that would be to go find a '93 V8 engine harness, PCM, and matching 5.0 distributor and strip all the explorer electrical and EDIS parts off the motor. Other than that V8 engine towers and mounts would be needed, a rad and hoses, and a matching flywheel or flexplate for whatever trans the truck has. This is a bit of work but it would use all the factgory parts so it would look like the truck came with the motor, and the Explorer V8 makes about 100hp more than the I6.

Oct 11, 2021 | 12:47 PM

#25

67 hoopty

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Joined: Jun 2014

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Quote:

Originally Posted by My4Fordtrucks

Your ‘93 doesn’t have the “crappy dual tank selector.” Each tank has its own high pressure fuel pump. What transmission do you have? Have you checked the fuel pressure and for fault codes? The check engine light does not have to be on for there to be codes stored in the memory.

So what's this on my 93, 5.0? Left side frame rail next to the front tank.

Oct 11, 2021 | 01:52 PM

#26

Scndsin

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Joined: May 2006

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From: Central Mississippi

Quote:

Originally Posted by 67 hoopty

So what's this on my 93, 5.0? Left side frame rail next to the front tank.

Who knows?

We can't get answers to fundamental question:

Does selected pump prime at key on/no start for 1-2 seconds then shut off? Yes/No, continues to run.