Front tank fuel pump
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New User
Joined: Feb 2007
Posts: 16
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Front tank fuel pump
Hello folks!
I have a question that I searched the forums regarding and found some good information but nothing exactly like what is happening to me. So, I would love any/all advice you can provide.
I have a 1990 F-150 with a 351, auto transmission, 4x4, etc. When I run off the rear tank I get regular performance and excellent reliability. If I run off the front tank, it responds normally when depressing the throttle up to 30-40% or so but begins to surge and hesitate at anything above that point. As I let off the gas, the hesitation goes away. So, this screams fuel pump to me, but here is the twist:
If I run off the rear tank, the rear tank seems to be filling the front tank? I intentionally siphoned out two 5 gallon cans worth from the front tank pouring it into the rear tank, then drove it using the rear tank for about 30 miles. I felt like the fuel gauge was going down drastically, from 3/4 at the start to just above 1/4 when switching back to the front. Lo and behold, the front was reading full again. Also, the front tank just always seems chock full, even to the point of overflowing when sitting in the sun.
Any advice on what is going on here folks?
Thanks everyone!
I have a question that I searched the forums regarding and found some good information but nothing exactly like what is happening to me. So, I would love any/all advice you can provide.
I have a 1990 F-150 with a 351, auto transmission, 4x4, etc. When I run off the rear tank I get regular performance and excellent reliability. If I run off the front tank, it responds normally when depressing the throttle up to 30-40% or so but begins to surge and hesitate at anything above that point. As I let off the gas, the hesitation goes away. So, this screams fuel pump to me, but here is the twist:
If I run off the rear tank, the rear tank seems to be filling the front tank? I intentionally siphoned out two 5 gallon cans worth from the front tank pouring it into the rear tank, then drove it using the rear tank for about 30 miles. I felt like the fuel gauge was going down drastically, from 3/4 at the start to just above 1/4 when switching back to the front. Lo and behold, the front was reading full again. Also, the front tank just always seems chock full, even to the point of overflowing when sitting in the sun.
Any advice on what is going on here folks?
Thanks everyone!
Elder User
Joined: May 2005
Posts: 537
Likes: 0
From: Graves County, KY
Sounds like 2 things are happening.
A. Front pump is weak
B. Fuel selector valve is failing and pumping gas from rear to front tank.
B can cause A since it is effectively fighting the normal flow of gas. Replace the Fuel selector valve on the frame rail.
A. Front pump is weak
B. Fuel selector valve is failing and pumping gas from rear to front tank.
B can cause A since it is effectively fighting the normal flow of gas. Replace the Fuel selector valve on the frame rail.
Lead Driver
Joined: Nov 2002
Posts: 9,557
Likes: 44
From: Concord, NC
1990 should have been the first year for high pressure in-tank pumps, with the switching valves built into each tank's sending unit or fuel delivery module (FDM). If this is the case, the fix will be to replace the front tank fuel delivery module/pump assembly.
Senior User
Joined: Oct 2001
Posts: 178
Likes: 0
If it were mine. I would pull the tank out and check that your screen isn't just full of crud and clean the tank out at the same time if the pump is running there is hope. Get your self a spray can of kroil to loosen up the long rusty tank hold in bolts and the ring on the top of the tank. Kroil is a god send for these jobs.
The fuel transfering from the back to front though is a bad sign. If the check valve can not be cleaned a new front pump assembly is in order.
The fuel transfering from the back to front though is a bad sign. If the check valve can not be cleaned a new front pump assembly is in order.
Last edited by acogoff; May 28, 2008 at 07:13 PM. Reason: add more info
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Super Moderator
Joined: Jan 2008
Posts: 40,024
Likes: 1,519
From: Maine, Virginia
If it were mine. I would pull the tank out and check that your screen isn't just full of crud and clean the tank out at the same time if the pump is running there is hope. Get your self a spray can of kroil to loosen up the long rusty tank hold in bolts and the ring on the top of the tank. Kroil is a god send for these jobs.
The fuel transfering from the back to front though is a bad sign. If the check valve can not be cleaned a new front pump assembly is in order.
The fuel transfering from the back to front though is a bad sign. If the check valve can not be cleaned a new front pump assembly is in order.
If you value your time, take heed. Change your pump, sending unit and do a thorough inspection of your tank. Tim
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