This morning I started my truck and I am sitting a very nice 18psi at idle and 15.5psi at WOT, nothing wrong here just normal everyday stuff. Temp outside is 68*F around 2pm

 

Just now I went to the corner store and I started my truck, mind you there is not hard start, and I noticed the fuel pressure is sitting at 12psi at idle and 10.5psi at WOT(for a very short run). Now the only conditions that have changed is the weather. It is currently 9:15pm outside and the temp is 30*F. Now I am hoping this is just because the temp difference is such a drastic change that the fuel is thicker? I also have a little less than a 1/4 tank in the truck. 

 

Is my fuel pressure this low because of the drop in temp outside or do I need to look into something else?

You are not cold enough for the fuel to be the issue unless you have a healthy dose of bio, I run straight untreated #2 to about 0-10* with no issues.What do you have for an in tank pickup tube?I have heard of many times the fuel gauge is off or the fuel pickup is cracked or too far off the bottom and sucks air.

Edited December 30, 201311 yr by Wild and Free

I have the modified liberty module from Vulcan Performance. I think it's a DS1 style? The only thing I can think of is the fuel gauge might be off but it is weird that is was doing fine earlier in the day...? That Vulcan Module better not be sucking any air!!!

http://www.vulcanperformance.com/Modified-liberty-fuel-module-p/fmds.htm

 

^Like this?

 

I had to do the mod entailed in the instructions with my 165. It involved modding the existing fuel basket, but this looks similar. I dunno if this one offered on VP is modded the same way as described in my instructions, though. I know AD told me to drill a couple holes in the fuel basket to allow more fuel to reach the draw straw, etc.

 

You should not be sucking air with the basket unless the basket is not allowing enough fuel. Which MIGHT be possible since the original basket design was only rated for the OEM lift pump. I do not know the flow volume of the OEM pump.

 

The key to this might be the fact that it occurs at your 1/4 tank mark. I would fill the truck up again and see if it persists when it gets to the 1/4 tank level. If that is the case, despite having this basket, it may not be allowing enough fuel into the basket. Which then you would just need to drill some holes into it to allow more fuel.

 

I have had an issue with my regulator in my AD100 twice now. The ball gets wedged in the spring and the pressure dropped by 3-5 psi each time. The second time it happened I tweaked the end of the spring in towards the center to prevent the ball from getting wedged again.

@ Hexorz, Yes that is the unit. I am going to put more fuel in it to see what happens today.@diesel4life, that is interesting you say that. I hope that isn't the case since this unit is less than a month old.

It only takes a few minutes to pull the ball and spring to check, and is an easy fix if that is the case.

Update***

 

 

 

I started it up this morning at 28*F and the pressure is now at 9.5psi at idle. I thought surely this HAS to be a temperature issue....well I was wrong. I also drove to the pump and put $30 in the tank and it is now well over a 1/4 tank. Still the same issue...9.5psi at idle. SO I drive the truck to work. There is no surge, hiccup, loss of power, nothing major going on again. 

 

Well, as I am driving I notice about 5 miles down the road I am at 8.5psi while cruising. As I come up to a stop light I am now 9psi idle....strange.... I am losing fuel pressure on the go now!! So I keep driving. I am now at my work about 20mins later and as I pull up to my work to park I notice the truck is now at 8psi at idle! WTF?!?! As I was driving somehow it was losing pressure VERY slowly. I still can't tell if it's the gauge or maybe the dumbass isolator I got from Vulcan or could it be the spring and ball already taking a **** with less than 600 miles on this pump??

It definitely is not temperature related, that is nowhere near cold enough to cause any problems. Since it is free, take the 10 Minutes to pop the ball and spring out and make sure it isn't wedged. It won't cost a thing. If there is nothing wrong there then your going to have to get your hands on another gauge to check fuel pressure to eliminate a gauge/sender problem. This is exactly why I prefer a mechanical gauge, there is no second guessing. Another thought is the overflow valve on the VP. Do you know how old it is? It could be possible it is failing and allowing fuel to dump back through the return line.

Edited December 30, 201311 yr by diesel4life

Time to ditch the gauge isolator. 99% of all gauge or low fuel pressure problems stem back to a isolator issues.

It definitely is not temperature related, that is nowhere near cold enough to cause any problems. Since it is free, take the 10 Minutes to pop the ball and spring out and make sure it isn't wedged. It won't cost a thing. If there is nothing wrong there then your going to have to get your hands on another gauge to check fuel pressure to eliminate a gauge/sender problem. This is exactly why I prefer a mechanical gauge, there is no second guessing.Another thought is the overflow valve on the VP. Do you know how old it is? It could be possible it is failing and allowing fuel to dump back through the return line.

 

 

I have a mechanical gauge, but I feel the isolator is causing a problem some how? The overflow valve? How do I check this? I don''t have another mechanical gauge btw.

Edited December 30, 201311 yr by Kotta390

Time to ditch the gauge isolator. 99% of all gauge or low fuel pressure problems stem back to a isolator issues.

 

 

Yeah its possible.

Gotcha, then like Mike says get rid of the isolater and get a needle valve. Should be able to get one at an auto parts store for a few bucks. That's most likely the issue.

Quick question if that is the case. Does the needle valve go inline with the tubing? IE: I remove the isolator and plug in a needle valve? 

Yes. The needle valve just needs to go inline in the tubing before the gauge. Then just open it a crack, just enough to get pressure to the gauge. This will cut the water hammer from the pump but allow the gauge to work correctly.

Yes. The needle valve just needs to go inline in the tubing before the gauge. Then just open it a crack, just enough to get pressure to the gauge. This will cut the water hammer from the pump but allow the gauge to work correctly.

 

 

What about having air in the line itself? It took me forever to try and "bleed" so to say the line when I was filling it with coolant. 

Has your fuel filter been changed lately?

Has your fuel filter been changed lately?

 

The fuel filter that came with the airdog is I think 3 micron filters and they have less than 600 miles on them. So to answer the question, now I havent but I shouldnt have to at this point.

I had to drive it again just now and the fuel pressure is now 5psi and when I got to my destination it is 4psi. Seems like there is no difference or fluctuation of fuel pressure anymore, no matter if I stomp it or cruise.

Here is how my isolator is tapped for fuel and then it converts that into the little clear tube that has anitfreeze in it. How do I convert the bog line to the snubber and then back to the clear tube?

 

 

My advice is to go all the way back to where the line for the gauge tee's off from the main fuel line. Start there with the needle valve and just use the small nylon tubing all the way to the gauge. Thats what most of us with mechanical gauges did I believe. This way if you ever had a problem with the tubing or the gauge you could shut the needle valve off at the source.