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Fuel Pressure dropping

6874 Views 5 Replies 4 Participants Last post by  hutt1
I have an 05 6.0 with 160,000 miles on it that the fuel pressure was about 45 psi at idle and went below 40 under load. I installed a blue spring kit and the pressure at first was about 65 psi and fairly steady even under load. All is good. Now after a couple months the pressure has dropped to 40 at idle and the auto meter gauge I have installed fluctuates constantly. Filters were changed about 10,000 miles ago. Truck runs good, no power loss and no codes. Just lower fuel pressure. Any ideas?
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I would start by checking the spring in the pressure regulator because its free to do so. Its possible that its taken a set. You can try stretching it by pulling both ends away from the middle a bit. Don't get crazy and stretch it way out, just try to get it to be a little longer.

If that doesn't solve the issue I have to suspect the fuel pump. The pressure regulator can only set the pressure at a certain psi if its getting enough fuel to build that much pressure. If the pump isn't moving enough fuel then the regulator can't build that 60psi because there isn't enough excess volume being pumped into the system to build 60psi. There is probably a way to do a volume test on the pump, but I don't know how to do it, or what the spec should be. Pumps are usually rated in gallons or liters per hour, so the typical test involves cycling the pump on for one minute and discharging fuel into a graduated measuring vessel. You see how much fuel it moved in one minute and multiply by 60 and that's you're volume per hour. It either meets spec or falls short, and if it falls short the pump is bad. The key though is knowing what the spec is.

If the pump is bad I would suggest installing a FASS or AirDog system instead of just replacing the stock pump. These systems are more stout than the stock one and provide a bigger filter and water separator. The filter change interval also goes from 12,500 miles to 50,000 miles. Cost wise its a bit more than a stock replacement, but peace of mind wise its money well spent.
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I agree. I misread that as 1,000 the first time. 10,000 is the interval at which I change mine; every other oil change so its easy to remember.
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