Need Some Help Guy's (Fuel system pressure way to high but the trucks happy) WTF

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OBXdieselAddict

New member
So my issue is trying to get my AirDog2 200GPM to give my LB7 8lbs of pressure. The pump has a Duramax spring in it and I know I can do the trick to clip half of a turn of the spring off to drop pressure more. I was told that the 200gpm is to big of a motor which I know it is but I don't see why at the right Lbs of pressure why it would matter. It wouldn't hurt the CP3 to return the excess fuel to the tank right?

My issue is that the truck doesn't want to go that low. With the pump all the way down right now I am flowing 21lbs. Truck idles just a tad bit ruff like its getting to much fuel but when you try to put it in gear and drive it dies like its not getting enough fuel. When it is turned up past 30lbs it idles fine and drives fine.

Is this just a weird platue that I need to go under and it will be happy again once its low enough? Should I clip the spring and try to keep dropping pressure down to 8lbs?

CP3 is stock (about 10k miles on it)
65% over SAC sticks from Lincoln
return line to CP3 and all other lines from sump up to the CP3 are 1/2"
 
Yea that was my first thought was maybe the gauge was off. We connected a separate gauge to the base of the AirDog and it was spot on to what my ISSPRO performax was saying.

I'm so confused. I drove the truck to work this morning and it was sitting at 28lbs and acted completely normal. I'm worried the CP3 may not be happy with it for long though. I'm thinking maybe I should just cut the spring down like AirDog said some guys have done in the past and try dropping it down to 8lb. I'm just confused why it seems to get worse the lower I get. You would think it would be the other way around.
 
Our original thought was that the gauge had to be wrong and maybe a regulator had gone bad on either the AirDog or CP3 but no matter where we tapped in we got the same pressure readings.
 
BigPapa said:
Who told you this?
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One of the guys I spoke to at AirDog, I didn't think that made much sense. I mean I feel like as long as the pressure is correct the truck wont care that more fuel is flowing to the cp3. Isnt that what the return line is for anyway? to return the fuel that doesn't make its way to the motor back to the fuel tank?

I found an old video of my truck at idle and before this pump I was sitting at 12lbs at idle and it was perfect.

I still haven't pulled the spring out but I guess I will try cutting the spring down just a bit to lower the pressure down and see if I can get back down to that level. I haven't ever pulled the spring out so I'm a bit nervous. My buddy said it was pretty simple its just behind the fitting that you adjust your pressure on the housing of the AirDog.

What are your thoughts about my little predicament? lol

I am hazy as hell at idle, IdahoRob made the tunes for having the 65 overs in it so I'm figuring its more my fuel pressure that's still my main issue not tuning. I also have noticed that in my bigger tunes if I get into it more then 50% throttle my rail pressure goes to S*%#. Could that also be a factor of my fuel pressure being to high?
 
BigPapa said:
If the manufacturer tells you it's too big, I'd listen to them.
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I think I may have actually gotten it solved.

I finally got around to pulling the spring out and clipped it down. Got the pressure down to 10lbs and its a night and day different. Truck runs great now.
 
In regards to the too big of a lift pump comment, air dog and Fass are in argreement with that but a Fass employee off the record stated the reason they state that is guys buy a huge pump with hopes in the future of big power but never do it, so much of the fuel has to be returned to the tank, on stock return lines that is a lot of back pressure. The other reason is the pump also has to return fuel to the tank as well, so you are taxing the pump harder than if you just bought the correct size lift pump.
 
Justappumped24v said:
In regards to the too big of a lift pump comment, air dog and Fass are in argreement with that but a Fass employee off the record stated the reason they state that is guys buy a huge pump with hopes in the future of big power but never do it, so much of the fuel has to be returned to the tank, on stock return lines that is a lot of back pressure. The other reason is the pump also has to return fuel to the tank as well, so you are taxing the pump harder than if you just bought the correct size lift pump.
Click to expand...

Thanks for the help. That's kind of what I figured by what he said. I do plan on dual fueling it before long and stepping up to an s475 but I'm a bit nervous about stepping the fuel up to much more without doing some bottom end work. I don't want to blow it up.
 
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