Fuel Pressure Gauge Readings
Thread Starter
Registered User
Joined: Mar 2004
Posts: 3,988
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From: Nebraska
Fuel Pressure Gauge Readings
I just installed my FP gauge (post filter, center boss) and I have a few questions. The readings vary widely. WOT I have a steady 6psi, but around around 55 miles (steady) it will fluctuate from 3 to 10 psi. Idle is the same thing. Is this normal? I replaced the LP about 20K miles ago so it should be okay.
Anybody else see these readings or is my LP going south? I have air in the gauge line, (no isolator) but that should not make a difference right?
I did a volume check and it pumped like crazy! Filled a quart jar in about a min. with the engine running.
Now I know why DC does not put gages in the trucks.
Buyers would ask too many dumb questions!
Anybody else see these readings or is my LP going south? I have air in the gauge line, (no isolator) but that should not make a difference right?
I did a volume check and it pumped like crazy! Filled a quart jar in about a min. with the engine running.
Now I know why DC does not put gages in the trucks.
Buyers would ask too many dumb questions!
Administrator / Scooter Bum
Joined: Sep 2002
Posts: 9,090
Likes: 52
From: Central VA
I agree.
Your readings should not be below 8psi even at WOT.
Idle should be in the 14-16 psi range.
Do not buy the replacement pump at the dealer (unless you're getting it covered under warranty)
Go to a Cummins Parts House and save yourself about $100-$150 for the replacement part, wiring pigtail, and the 4 washers needed.
Should be a 45 minute to an hour job.
Your readings should not be below 8psi even at WOT.
Idle should be in the 14-16 psi range.
Do not buy the replacement pump at the dealer (unless you're getting it covered under warranty)
Go to a Cummins Parts House and save yourself about $100-$150 for the replacement part, wiring pigtail, and the 4 washers needed.
Should be a 45 minute to an hour job.
Thread Starter
Registered User
Joined: Mar 2004
Posts: 3,988
Likes: 7
From: Nebraska
It was the pump! I took your advise and replaced it. 16 psi at idle, 10 at wot. Thanks man!
I'm just real happy I put the gauge in and caught the problem. It was wandering all over and I thought for a while the gauge was wrong since I replaced the pump a while back.
NEW QUESTION.... How does the pump maintain pressure? Is there a sensor in the pump to regulate it or is it wot all the time? I know the pump cuts the pressure when starting so the VP-44 will work properly. Too much pressure is not good either.
Looking at the old pump after I took it apart (its my nature) I cannot beielve anyone would send used oil through their fuel system. There is NO FILTER before the pump. IMHO
I'm just real happy I put the gauge in and caught the problem. It was wandering all over and I thought for a while the gauge was wrong since I replaced the pump a while back.
NEW QUESTION.... How does the pump maintain pressure? Is there a sensor in the pump to regulate it or is it wot all the time? I know the pump cuts the pressure when starting so the VP-44 will work properly. Too much pressure is not good either.
Looking at the old pump after I took it apart (its my nature) I cannot beielve anyone would send used oil through their fuel system. There is NO FILTER before the pump. IMHO
Thread Starter
Registered User
Joined: Mar 2004
Posts: 3,988
Likes: 7
From: Nebraska
I tore apart the old pump and figured out the pressure is regulated by a ball and spring check valve set up. I cannot believe they mount this pump to the motor. Too much vibration from the motor for the pump to live very long. A pump this delicate should be isolated from the motor. IMHO
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