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I have a GMC 7500 . cat c7 motor . I had oil into my fuel tanks…

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I have a GMC 7500...
I have a GMC 7500 . cat c7 motor . I had oil into my fuel tanks always started up thou. Replaced o rings and fuel pump.. Now it only turns over and doesn't start.. What could be my problem ..it shows nothing on a scanner.. Thx.
Submitted: 3 years ago.Category: Medium and Heavy Trucks
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Answered in 2 hours by:
6/16/2015
Technician: Cat Man, Cat Engine Expert replied 3 years ago
Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 9,459
Experience: I am ASE Master Truck Certified.
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Hi. Thanks for asking your question! I will try and help you out.
It sounds like you may have a low fuel pressure problem. If air was put into the tank and the engine started. I would check fuel pressure first.
The engine needs at least 25 psi to start. Your engine should maintain a fuel pressure between 75 and 90 psi when running. There is a plug beside of the secondary fuel filter that is used to check the pressure. If it is low, I would first try the fuel filters if you haven’t already. If it is still low, you may have a failed fuel pressure regulator, which is located underneath the bottom of the filter housing. I have replaced a ton of these for low fuel pressure. It is kinda a known problem. You could also have a weak fuel transfer pump or restricted hand primer pump, if your engine has one.
Please reply back if you need more help or have more questions. I am happy to assist.
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