High pressure pump bad?
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Junior User
Joined: May 2011
Posts: 74
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From: roxboro N.C
High pressure pump bad?
Have a 1987 4.9 auto That wont crank. Fuel pressure when you first turn the key is around 10 to 15. Keep on turning the key to on it slowy builds up pressure each time. Can hear the pump come on each time for a few seconds. My thinking is the first time the pump is activated it should go up to around 40 or so. Am i correct in assuming it needs a new pump? It has a new filter and a new low pressure pump in front tank. Only running from the one tank
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
The fuel system should build and hold close to 60psi for the 4.9, and the 'pre '90 trucks have a more complicated fuel system with low pressure pumps in the tanks and a high pressure on the frame next to a "switching" valve and filter. So first thing to do is determine if both pumps are working and if so the problem is with the valve or because of a clogged filter.
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