Fuel Pumps
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Junior User
Joined: Sep 2010
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From: St. Johns
Fuel Pumps
I have 32 psi on my fuel rail and when my truck starts to die so does the psi. I have already changed the fuel pressure regulator. I have both fuel pumps low pressure in the tank and high pressure on the frame. Can anyone tell me how I can test both pumps to figure out which one it is.
Cargo Master
Joined: Jul 2009
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From: Des Moines
Well if you've got a high pressure pump on the frame and the pressure is dropping at the fuel rail, I'd guess that it's the pump on the frame as opposed to the pumps in the tanks.
But I'm not familiar with the systems that have the pump on the frame either, so that's just my guess.
But I'm not familiar with the systems that have the pump on the frame either, so that's just my guess.
Postmaster
Joined: Mar 2008
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From: Des Moines, Iowa
DB has it right... Make sure you have the problem with both tanks. Most likely you don't have the same problem at the same time with both in tank fuel pumps.
If you have a problem with just one tank, then it will be an in tank pump problem.
If you have problems with both tanks not able to get the fuel to the rails, then it will be your fuel pump on the frame.
remember to replace your fuel filter too... It could be causeing you problems if it has been used for way longer than recommended... I usually replace mine every 36-48 K or 3-4 years... some will say sooner and others would say longer... depends on how much fuel you put through the truck...
If you have a problem with just one tank, then it will be an in tank pump problem.
If you have problems with both tanks not able to get the fuel to the rails, then it will be your fuel pump on the frame.
remember to replace your fuel filter too... It could be causeing you problems if it has been used for way longer than recommended... I usually replace mine every 36-48 K or 3-4 years... some will say sooner and others would say longer... depends on how much fuel you put through the truck...
Postmaster
Joined: Mar 2008
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From: Des Moines, Iowa
i don't have a fuel pressure tester myself, but would think you could test the fuel pressure from the line that leads to the high pressure pump on the frame... not sure of the pressure that should be coming from the tanks and what should be coming from the final high pressure unit, but I am sure someone on here does...
Post Fiend
Joined: Mar 2002
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From: Bonita Springs FL
The in-tank pump just supplies the high pressure pump with fuel. If you are having fuel pressure problems and you've eliminated all other possible sources (kinked lines, clogged filters, etc.) then replace the high pressure pump first.
New User
Joined: Apr 2009
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When you removed side tank, did you take out the tank switching valve on the rail? If not it could be stuck between the two tanks and if in tank pump does not have enough pressure(clogged with rust or just weak). It would not be able to switch to rear tank. Happened to my 89. Just a thought, hope it helps.
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Junior User
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From: St. Johns
is there any way to test the switching valve before i put this new high pressure pump in? the thing is, is that i bought the truck back in may had no problems with it till a week ago or so and it made the trip from indiana to florida no problems. the front tank had already been removed from truck before i bought it.
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From: Easton,Ks
Sounds like you may have a bad distributor (PIP sensor).
It is unlikely you have a fuel problem if you turn on the key and the pumps pump 32 PSI and the engine starts and then then dies from lack of fuel.
Check for spark as soon as it dies.
It is unlikely you have a fuel problem if you turn on the key and the pumps pump 32 PSI and the engine starts and then then dies from lack of fuel.
Check for spark as soon as it dies.
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Junior User
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From: St. Johns
The distributor is new the cap is new the coil is new the rotor is new and I'm still getting spark when it dies. I have 32 when it starts up but as it starts to die the psi drops. The fuel filter is 2 months old. I've checked the tps, egr, map, opened the comp to check for any broken soders or heating all was good. check all my plugs and wires they're all good. Changed a broken vac line to the egr and the broken gasket for the throttle body. I put a new gas cap on as well.
Fleet Owner
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From: Easton,Ks
Then it would be the selector valve, the fuel filter or the high pressure pump.
Take the fuel line off the selector valve that goes to the high pressure pump and turn on the key. If you get fuel out of the valve then change the pump.
By rights you should ground pin #6 of the Self-Test plug when you do the test.
Take the fuel line off the selector valve that goes to the high pressure pump and turn on the key. If you get fuel out of the valve then change the pump.
By rights you should ground pin #6 of the Self-Test plug when you do the test.
Fleet Owner
Joined: Aug 2005
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From: Easton,Ks
Should have a good stream for one second at about 7-12 PSI.
Note that one second is longer than you might think.
If you short pin #2 to pin#6 of the EEC Self-test connector the high pressure pump and the selected in tank pump will run as long as the key is on.
You should also have 42 to 45 PSI at the fuel rail with the engine not running and the fuel lines all connected for a V-8.
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Note that one second is longer than you might think.
If you short pin #2 to pin#6 of the EEC Self-test connector the high pressure pump and the selected in tank pump will run as long as the key is on.
You should also have 42 to 45 PSI at the fuel rail with the engine not running and the fuel lines all connected for a V-8.
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Junior User
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From: St. Johns
I had a stream coming out of the line off the selector when I cranked the motor for a second or two. My old high pressure pump would wine while the truck would run. I put the new pump in and just ran the truck for 20 min at 55 mph and the problem didn't come back. I no longer have access to the fuel pressure gauge I used. If the problem occurs again it's a good assumption to assume it's the switch valve.
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Junior User
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From: St. Johns
Started the truck back up idled for 15 min then went to drive it down the street and the problem came back. Got it back in the driveway let it idle out it died and wouldn't crank back up.