Fuel pressure dropping below spec?
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From: Fairhope Alabama
Fuel pressure dropping below spec?
I just noticed this while driving just now. My truck has been using a lot of fuel lately and I found a leak on the bottom of the fuel / water drain valve and all the screws were loose. Which was my fault for being overly careful when tightening them down so I tightened them up and I put some napkins under it and couldn't get any diesel to drip down onto it so I figured I fixed it. Well, just now in a 65 HP performance tune, when I really get on the pedal I'm dropping down to 35 PSI of fuel pressure. It shoots right back up but when I first pushed the pedal it does drop way down. So, I'm thinking I either still have a leak or a clogged fuel filter which is not that old. The fuel filter does not have 15K miles on it for sure. It's hard to tell what is diesel or oil because my hpop is leaking oil so, everything has a coating of oil on it.
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From: Fairhope Alabama
My fuel light is on right now but, I got on the pedal pretty hard and I feel pressure drop down to 20 psi for a split second and then it jumped back up to 60, but right after that I took the truck out of gear and idled and the fuel pressure dropped to 50 and then kind of jumped back up to 60 slowly. It's acting really funky. I just replaced my fuel pressure regulator a while back so I don't feel like that should have anything to do with it. Does this sound like a leak? I wonder if being this low on fuel my compression fitting holding my Hutch mod in place is pulling air. I guess it's possible. I guess I'll have to add some fuel and see if it still does it. I feel like I probably just have a bad leak. I probably should replace the fuel filter just to be safe
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From: Muskogee, Ok
If you've ever watched your fuel pressure when you run the tank down below 1/4 you'll see that on decent acceleration and every stoplight decel the fuel pressure will drop down and come up a few times, the lower the tank level and harder the start/stop the more often and pronounced it will be. Fuel sloshes in the tank cause there's no baffles. It's basic physics of momentum. Get er above 1/2 tank and the slosh isn't as pronounced and won't affect the fuel pickup cause the fuel doesn't have the ability to go all fore or aft and have the momentum to overcome gravity in the area available in the tank.
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From: Fairhope Alabama
If you've ever watched your fuel pressure when you run the tank down below 1/4 you'll see that on decent acceleration and every stoplight decel the fuel pressure will drop down and come up a few times, the lower the tank level and harder the start/stop the more often and pronounced it will be. Fuel sloshes in the tank cause there's no baffles. It's basic physics of momentum. Get er above 1/2 tank and the slosh isn't as pronounced and won't affect the fuel pickup cause the fuel doesn't have the ability to go all fore or aft and have the momentum to overcome gravity in the area available in the tank.
I still think it is possible that I have a diesel leak and I pray it is not the fitting on the rear of the head that I redid while I had the turbo off because it is very hard to get to with the turbo on. With as much oil that is leaking out of my hpop it is hard to see if there's actually diesel anywhere cuz there is currently oil everywhere. The reason I started thinking about a diesel leak is because my fuel mileage was worse than it was before. Of course I now have 35 inch tires and a tuner and a big Turbo. I used to get 23 miles to the gallon on the interstate which was amazing. I went to get my transmission from Louisiana and got like 16 miles to the gallon which is quite the jump but going from 28 inch tires to 35 in tires and adding a tuner is probably why that happened. Does 16 MPG sound about right?
I think I'm going to get some of that fluorescent dye and put in my tank and use a black light to see if I can pinpoint a leak if there is one just in case
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From: Muskogee, Ok
Depending on where you got fuel you might have got some winter fuel if you traveled North. If you got it at Luvs you can usually expect to loose mpg vs other suppliers. Granted large tires, higher truck ride height, many alignment issues, could all lower mpg a tiny bit on their own. Even a slightly dragging brake will drop it.
Since you're not running sick tires have you at least recalibrated your speedometer? You'll be covering more distance per rotation so actually getting better mpg than your odometer and hand calculation would show, unless you use a GPS to track every single drive and add up the distance per tank
Since you're not running sick tires have you at least recalibrated your speedometer? You'll be covering more distance per rotation so actually getting better mpg than your odometer and hand calculation would show, unless you use a GPS to track every single drive and add up the distance per tank
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From: Fairhope Alabama
Depending on where you got fuel you might have got some winter fuel if you traveled North. If you got it at Luvs you can usually expect to loose mpg vs other suppliers. Granted large tires, higher truck ride height, many alignment issues, could all lower mpg a tiny bit on their own. Even a slightly dragging brake will drop it.
Since you're not running sick tires have you at least recalibrated your speedometer? You'll be covering more distance per rotation so actually getting better mpg than your odometer and hand calculation would show, unless you use a GPS to track every single drive and add up the distance per tank
Since you're not running sick tires have you at least recalibrated your speedometer? You'll be covering more distance per rotation so actually getting better mpg than your odometer and hand calculation would show, unless you use a GPS to track every single drive and add up the distance per tank
I do still feel just for the sake of doing it I should get some dye to put in my tank and a black light.
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From: Muskogee, Ok
5 off at what speed? @ 50 and the math is easy enough to do in your head. @ 63mph you might need to take your socks off for the math 
If it happens to be @ 50mph your actually doing 55; or 10% more, so you can ad 10% to your mileage before you divide by gallons. Still that would only take your 16.6mpg up to 18.2 ; a far cry from 23.
Those new wider tires have more rolling resistance than the narrower stock tires tho. Which is the downside to a wider contact pad which helps with braking and weight dispersement per psi on unpaved roads or yards.
If it happens to be @ 50mph your actually doing 55; or 10% more, so you can ad 10% to your mileage before you divide by gallons. Still that would only take your 16.6mpg up to 18.2 ; a far cry from 23.
Those new wider tires have more rolling resistance than the narrower stock tires tho. Which is the downside to a wider contact pad which helps with braking and weight dispersement per psi on unpaved roads or yards.
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From: Fairhope Alabama
I was going 70 for most of the trip. Although I did a lot of testing on my new turbo while I was on the interstate if you know what I mean. Can't complain about fuel mileage when I'm having fun LOL
but yes at 50 mph it is off by 5 mph. Hey, 18.2 is pretty good mileage considering my truck weight 7680 with my mounted tool boxes and fuel. I can live with that!
but yes at 50 mph it is off by 5 mph. Hey, 18.2 is pretty good mileage considering my truck weight 7680 with my mounted tool boxes and fuel. I can live with that!
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