I get fluctuating fuel pressure when I run my bio up to aproximately 45-50%. The percentage is rough I always just do a quick calculation in my head. Anyhow my airdog gives me 17-18 psi normally. When I run say over 35% of bio it usually drops down to 14-15 psi. Then when I approach 45-50% the fuel pressure will hold at 14 then drop to 5 or sometimes even zero. Then pop back up to 14 and repeat seemingly without a pattern. Sometimes it may take a few minutes to do this and others it will do the whole deal in 10 seconds. If the fp falls to zero my rp will still usually hold until about 50% of load (just a guess).

When it does this I usually just add a few gallons of #2. It quits fluctuating and everything is happy again.

My theory is that my airdog just doesn't like the viscosity of this bio. My buddy brews it. He does a very good job as far as I know and can tell. His setup is legit well filtered and all that.

So my main question is are any of you pushing as much fuel as I am or more (sorry I can't quantify how much fuel beyond saying it is 600hp+ worth) with an Airdog, Fass or similar fuel delivery system and having issues with fuel pressure? Airdog is a 150 BTW. Supply line is run to the stock filter housing and pressure sensor is installed just after the factory filter.

Also I want to add I can easily see the difference in how thin or thick the fluid is when I'm having issues by sampling some of the fluid. Also temperature seems to have no major effect on this problem. IIRC I've had a 42% mixture in weather down to 25 degrees.

Today the mixture was thick enough that after the fp dropped to 0 the cp3 was starved and the truck died.

You don't need to have a 600hp truck to respond, I just threw that out there to possibly draw someone with a similar setup. If you've seen issues like this and or have alot of experience with bio, lay it on me.

Thanks

Roy - Maybe check with Justin and see what he is seeing. I know he is running lift pumps, and I THINK he is around 500.

I run bio in mine and have not seen any issues in retail bio of up to 80%. I have seen a few problems with homebrew.

I run bio in mine and have not seen any issues in retail bio of up to 80%. I have seen a few problems with homebrew.

Well the fact that you run the same pump is throwing me off a little bit. Just to verify how sure are you about your 80%? Is your retail bio less viscous I wonder? Also as Rockin said above my buddy runs the same fuel obviously not the exact same batch, but bio made to the same standards and has zero fp issues.

I really want to say it is just the thickness of the fuel that is causing the issues.

I've been running amounts of bio and I don't have a pressure gauge on my line but I've wondered about the stock fuel filter being able to filter the thicker fuel and still provide enough fuel to the motor at higher hp levels (looking at around 480hp for me) I got a cat filter setup that I'm making that will replace the factory filter.

This problem is on your dodge? I think the filters on those are a little larger but I attached a pic of the size difference between the stock duramax filter and cat's filter.

I think you may have a lift pump issue. Like I said before, I don't have any problems with mine, thus far. Unless the OEM filter is giving you issues, I can't see that anything else would be suspect.

Have you tried running it without the OEM filter?

Sent from my Evo Shift using AutoGuide App.

I've been running amounts of bio and I don't have a pressure gauge on my line but I've wondered about the stock fuel filter being able to filter the thicker fuel and still provide enough fuel to the motor at higher hp levels (looking at around 480hp for me) I got a cat filter setup that I'm making that will replace the factory filter.

This problem is on your dodge? I think the filters on those are a little larger but I attached a pic of the size difference between the stock duramax filter and cat's filter.
Sold the Dmax a long time ago!

I think you may have a lift pump issue. Like I said before, I don't have any problems with mine, thus far. Unless the OEM filter is giving you issues, I can't see that anything else would be suspect.

Have you tried running it without the OEM filter?

Sent from my Evo Shift using AutoGuide App.

Could be the pump itself. This is my second airdog, which replaced the first one that failed. I really can't see the O.E.M. filter being the culprit, but it is a possibility. Though there are a chit ton of guys using the exact same filter in the oem location without any issues. I may at some point remove it to make absolutely sure......may. I'm pretty sure for whatever reason my particular airdog just doesn't like the thick fluid.

Thanks for the reply's.