Fuel Pumps????
New User
Joined: Oct 2002
Posts: 1
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From: San Antonio
Fuel Pumps????
I have an '89 F-150 with an Inline 6 cyl 4.9L engine. When I start the truck it imediately dies and the keeps doing so until it has run for 4 or 5 minutes. I also recently have begun to notice a hesitation and inconsistent idle even when the truck has warmed up. The truck has two tanks and there is a high pitched whine near the external fuel pump when the rear tank is being used (whine goes away when other tank is used). The hesitation and inconsistent fuel pressure (idle) seem to happen when either tank is used. There are three fuel pumps on this truck (2 in tank and one external). Where do I start diagnosing? It would cost near $375 in parts to replace all three pumps and a lot of time to drop the tanks. I only want to do this job once and get it right the first time. Any help would be greatly appreciated. Thanks.
Senior User
Joined: May 2002
Posts: 310
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Fuel Pumps????
[updated:LAST EDITED ON 30-Oct-02 AT 03:08 PM (EST)]are you sure there's 3? I was told only 2 in the tanks. If so where's the external one? I've got a similar problem as you said above with the same engine.
Posting Guru
Joined: Jan 2001
Posts: 2,358
Likes: 3
From: Nebraska
Fuel Pumps????
Maybe it's the fuel pressure regulator causing your problems 
. Sprocket, older EFI trucks had a low pressure pump in each tank and a high pressure pump along the frame rail. Newer ones have a high pressure unit (fuel delivery module) in each tank.
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1995 F-150 Supercab XLT 155" 4x4 M5OD 302
1986 F-150 4x4 NP435 300
. Sprocket, older EFI trucks had a low pressure pump in each tank and a high pressure pump along the frame rail. Newer ones have a high pressure unit (fuel delivery module) in each tank. --------------
1995 F-150 Supercab XLT 155" 4x4 M5OD 302
1986 F-150 4x4 NP435 300
Elder User
Joined: May 2001
Posts: 662
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From: washington
Fuel Pumps????
yeah there is 3 pumps. The external usually isn't the one to go out. The one in my rear tank began to act up and I decided to replace both pumps. I just took the bed off and installed both. It is much easier to pull the bed off than pull both tanks out!
Senior User
Joined: Aug 2002
Posts: 363
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From: Woodbridge
Fuel Pumps????
I agree with pulling bed off! I had to replace my front fuel pump and my rear tank, both at the same time. And of course, this had to happen after filling both tanks two days prior! The bed can be removed by two people if you are careful. A third helps in spotting any connections to the fuel fill or wiring you might have forgotten.
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New User
Joined: Jun 2002
Posts: 22
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From: Shawnee
Fuel Pumps????
I have a similar problem with my 87' F150 and will replace mine soon also. But I want to drain the crap out of my tanks so I will be dropping them from below. It's something to think about if you suspect trash in your tanks.
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Elder User
Joined: May 2001
Posts: 662
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From: washington
Fuel Pumps????
My rig has 150K on it and the tanks were crystal clean. Is there a drain a the bottom of the tank? I haven't ever seen one! I actually did the bed myself. I rigged up the engine hoist (which I use a block and tackle and suspend it from the roof of my garage) and I hooked rope and chain to the 6 bed pockets and lifted it up. It was rather easy by myself and it took about 3 hours. The hardest part is breaking the nuts loose from the bed bolts. Make sure you soak them with some penetrating lube weeks before you begin!
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Senior User
Joined: Aug 2002
Posts: 363
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From: Woodbridge
Fuel Pumps????
I had better luck with taking the bed off. My '94 had little rust or boogered threads, and the nuts twisted off quickly. My brother and I had the bed off in 35 minutes. Now, getting the new pump in the front tank took a bit longer....
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