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87 GMC Sierra 2500 4x4 350 TBI fuel issue


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gypsy
New User

Sep 7, 2014, 12:44 PM

Post #1 of 7 (3496 views)
87 GMC Sierra 2500 4x4 350 TBI fuel issue Sign In

Fuel tank crossover went bad and started leaking around wiring plug in. I replaced it and only one tank would work (plumbing incorrect) it was returning to the wrong tank. I fixed the plumbing problem and it will not maintain pressure. I replaced the crossover and both pumps and now it will start and will run if you keep flipping the tank switch back and forth the minute you stop or stutter flipping the switch the truck dies. It is something I have never seen and am at a loss as to where to look next.


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

Sep 7, 2014, 2:51 PM

Post #2 of 7 (3482 views)
Re: 87 GMC Sierra 2500 4x4 350 TBI fuel issue Sign In

What is a crossover? Do you mean fuel tank selector valve? How was it running before you noticed the leak? What kind of fuel pumps did you buy? Did you make sure you didn't reverse polarity on the pumps? Have you made any voltage checks at the selector valve and the fuel pumps?





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


gypsy
New User

Sep 10, 2014, 7:03 PM

Post #3 of 7 (3452 views)
Re: 87 GMC Sierra 2500 4x4 350 TBI fuel issue Sign In

It was running fine prior to the first valve replacement. After the first replacement it ran fine but only on one tank, occasionally it did not want to start, but if you flipped the switch and then flipped it back it would start fine. After fixing the plumbing it ran fine on both tanks for about 3 hours ad then stopped running on one tank and overfilling the other tank. Both pumps are reading 10.3v on the left and 11.0v on the right.


Discretesignals
Ultimate Carjunky / Moderator
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Sep 10, 2014, 7:44 PM

Post #4 of 7 (3449 views)
Re: 87 GMC Sierra 2500 4x4 350 TBI fuel issue Sign In

From your description is almost appears you have some lines switched at the selector valve. Recheck your lines:



You may have another issue, but make sure your lines are connected properly. You shouldn't have one tank feeding into another.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Sep 10, 2014, 7:45 PM)


gypsy
New User

Sep 13, 2014, 7:39 AM

Post #5 of 7 (1698 views)
Re: 87 GMC Sierra 2500 4x4 350 TBI fuel issue Sign In

There had been some lines reversed. That was when I replaced the valve the second time thinking I had messed up the internals of the switch. Now it will run but only if the switch is being moved back and forth rather rapidly. As soon as the switch stops being moved the truck stops running.


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

Sep 14, 2014, 6:54 AM

Post #6 of 7 (1674 views)
Re: 87 GMC Sierra 2500 4x4 350 TBI fuel issue Sign In

What is fuel pressure doing or reading while your switching the tanks back and forth.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


gypsy
New User

Sep 25, 2014, 5:54 PM

Post #7 of 7 (1649 views)
Re: 87 GMC Sierra 2500 4x4 350 TBI fuel issue Sign In

Sorry it has taken me a bit to get back. I'm in the military so time is everything. I went back to troubleshooting 101 checked both pumps pressure is good, checked the voltage through the switch, both pumps worked on the proper setting, checked the valve itself and discovered that the left and right supply and return lines were switched. changed both supply and return lines to the proper place and it is running fine now. Thank you for your help.






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