problematic truck

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Oct 28, 2008 | 06:22 PM

89straightsix

Thread Starter

Freshman User

Joined: Apr 2006

Posts: 28

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From: Tulsa, OK

problematic truck

Well, my ford f150 has once again failed me, despite the money I have put into it. It has dual tanks, and the 16 gallon rear tank has been failing to work for a few months now with a full tank, but the front tank works. I have replaced the fuel filter and the fuel pump relay, but I am not sure if the problem is the pump or not. I believe the pump is in the tank, but I'm not certain. I am not an expert on these trucks obviously, but any input would be greatly appreciated. The truck is a 1989 model with a 4.9L six.

ryan

Oct 28, 2008 | 06:43 PM

reeds101

Junior User

Joined: Nov 2006

Posts: 73

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From: Mass

I'd have to say it's the pump itself, do you hear it working when you turn the key "on"?

Oct 28, 2008 | 11:25 PM

Boss429F150

Junior User

Joined: Oct 2005

Posts: 55

Likes: 0

if i remember right my 89 had the high pressure on the frame and the lift pumps in the tanks because my 91 has just 2 high pressure pumps in the tanks. And just by luck if the rear tank is full then ofcourse the pump is probably bad, lol. Just seems thats how it happens.

Oct 28, 2008 | 11:58 PM

ford2go

Cargo Master

Joined: Apr 2003

Posts: 3,476

Likes: 224

From: Frequently frozen MN

89 was nearly the last year of the 3 pump system. Low pressure pumps in the tanks just get the fuel down to the rail pump.

Could be pump, switch, the fuel filter sock on the in tank pump, or a few other things. ( I know most of this from other forum discussions)

I'd do everything that I could to make sure it was the pump because it's not fun to get to. Some guys here slide back the bed claiming that it's easier to do that than to drop the tank.

You could always live with it. I'm sure it's a PITA, but fixing it might not be easy.

Good Luck!

Oct 29, 2008 | 07:52 PM

deeznuts822

Elder User

Joined: Feb 2008

Posts: 797

Likes: 1

From: ohio

THE ONLY WAY I CAN GET MY REAR TANK TO WORK after switching tanks is to ground the fuelpump relay switch the switch and let the pumps rum for a few min. Then it will run on rear till i switch, when i do have to do it all over again

Oct 30, 2008 | 02:06 AM

BigSix1

More Turbo

Joined: Sep 2003

Posts: 630

Likes: 4

From: Northeast

Bad Tank Selector Switch?

The fuel tank selector valve, located on the driver's side frame rail, is not powered by electricity--rather, it uses fuel pressure to "shunt" a mechanical valve to allow it to draw from one tank or the other.

I'm wondering if your fuel pump selector switch/wiring is bad, and not telling the rear pump to pump?

But the tank selector valves themselves do go bad--I changed mine--$65. with employee discount, from the stealership.

Perhaps someone will post with a diagnostic routine you could run, to confirm/rule this out?

Good luck.

BigSix1

Oct 30, 2008 | 04:54 AM

ymeski56

Der Postmeister

Joined: Sep 2006

Posts: 6,859

Likes: 560

From: Long Beach, Calimexiforia

Quote:

Originally Posted by BigSix1

Two circuits com into the switch. One for pumps/one for gauges. Switch toggles direction of both circuits to front tank pump & sender or rear tank pump And sender. Testing (w/key on) the 4 circuits connections out to ground should show current at two of those connections w/ switch in one position & current at the other 2 when switch is in the other position. Gauge senders function w/wo pump function. If switched to rear tank & only 1 of the 4 are showing current(and fuel gauge showing tank level) than pump contact in s/witch is bad. If current through switch showed ok for pump connection also, I'de go get a selector valve at a salvage yard for $10. & replace the one on the truck before I embarked on a tank droppin pump replacement adventure.