Fuel Pressure problem, need help

[RJC2]

Alright guys, I replaced my lift pump a couple of weeks ago with an Air Dog 100, installed the draw straw V, and big line kit. Everything was going well and I had 16.5 PSI at idle, 13.5 at wide open throttle, consistantly. This evening I was running just below a 1/4 tank and stopped and filled up. Started the truck and had 16.5 psi. I drove 24 miles home and watched the fuel pressure drop slowly to 5 psi by the time I got home. The truck is running fine, and I see no fuel leaks under the truck. My first thought is "bad fuel" and the filters are clogging. I have an extra set of filters for the Air Dog and the factory filter which I plumbed in with the Air Dog. My first inclination is to change the filters and see if the pressure comes back up, but I thought I would pick your brains and wait till morning before doing anything.As a side bar. While filling up at the service station (which isn't the one I normally use) the pump was running very slow, so I got in the truck while filling up (28 gallons). An employee was standing in front of the store smoking a cigarette and walked over to me and asked if the pump was running slow and I said yes it was. He pointed out that all of the gas pumps had plastic bags over the nozzles because "they sell so much fuel that they ran out and diesel was all that was left.I don't know how much diesel was left in their tanks but I have to wonder if I got the bottom of the barrel!Any thoughts or suggestions are much appreciated.

[dripley]

if you did get the bottom of the barrel you might have pick up enough crap to clog the filters or maybe just the prescreen. i am assuming the 100 has two filters. there is a screen in the fitting that the wfs filter screws onto and it might be clogged. you have to take the fitting off to get to the screen. was the pump making unususal noise?

[RJC2]

Thanks for the quick response Dave. I just ran out and bumped the starter to see and it sounds like it normally does. It read 5psi when I shut it down an hour ago, now it has 3 psi. When the pump was running with a starter bump, engine off, I would hear what sounds like moments of air going through the line. A little swish, swish sound now and again. I took it as normal. I have the 17 psi spring in it. but have never seen that much pressure.Just before filling up I noticed it was sucking a little air when I would come down the mountain and hit the brakes. The fuel pressure dropped into the teens until the fuel sloshed back into the tank, nothing abnormal I thought. It would come right back up to 16.5. The fuel pressure did hit 17 for the first time just before I filled it up, only for a few seconds. I just thought that it was due to the fuel getting low.

[dripley]

i would think if it is making noises like you say it is either sucking air or cavitating because a filter is clogged and not letting fuel in. when mine runs it only makes the noise of the pump running. i did run mine dry a couple weekends ago and had to refill the filters to get the prime back.it really did not make any odd noises then. since you slowly lost pressure i would lean toward a clogged filter. you could take the wfs off and shine a flash light up at the screen and see if it clogged. it just sounds like dirt slowly building up until it stops the flow.

[RJC2]

Good idea Dave. I forgot about the screen. I will check it first. When you primed the filters did it start okay or did you have to bleed the injectors?Also, another question. When you take your Air Dog filters off does fuel just siphon out of the tank onto the ground from the Air Dog? It did for me and I had to put a clamp on the fuel line to stop the leaking fuel or it would have emptied a portion of the tank on me.The tank was full and the tank fuel level was higher than the pump. I kept waiting and waiting for that line to empty and finally it dawned on me that I had a siphon going.

[dripley]

Good idea Dave. I forgot about the screen. I will check it first. When you primed the filters did it start okay or did you have to bleed the injectors? mine was full of air and i did have to open the injectors. i opened 1 3and 4 and bumped the pump several times and let the pump push fuel up to the open injectors untill i saw some full coming out. then closed 3 and 4 and tried to sart it. if it doesnt start after a little cranking stop and bump the lift pump a couple more times and try to sart it. it should start. the lift pump will push fuel to the injectors and it is easier on the starter that way. Also, another question. When you take your Air Dog filters off does fuel just siphon out of the tank onto the ground from the Air Dog? It did for me and I had to put a clamp on the fuel line to stop the leaking fuel or it would have emptied a portion of the tank on me. The tank was full and the tank fuel level was higher than the pump. I kept waiting and waiting for that line to empty and finally it dawned on me that I had a siphon going.

the only time i have taken mine off the lines were full of air so no siphon. but i will look out for that one. that could get messy and . if that happened to you tonight it sounds like the lines are not leaking any air and the problem is in or after the pump. there are two answers up there i buried one in your quote.

[RJC2]

Yeah, I'd venture a guess that it is the fuel contaminated. At least I am all brushed up on how to do it. (taking the tank off) and siphoning 30 gallons of diesel... well lets just say the wife won't want to kiss me for a while. Burp! EEEW whats that smell, Diesel fuel honey.

[dripley]

Good idea Dave. I forgot about the screen. I will check it first. When you primed the filters did it start okay or did you have to bleed the injectors? Also, another question. When you take your Air Dog filters off does fuel just siphon out of the tank onto the ground from the Air Dog? It did for me and I had to put a clamp on the fuel line to stop the leaking fuel or it would have emptied a portion of the tank on me. The tank was full and the tank fuel level was higher than the pump. I kept waiting and waiting for that line to empty and finally it dawned on me that I had a siphon going.

Yeah, I'd venture a guess that it is the fuel contaminated. At least I am all brushed up on how to do it. (taking the tank off) and siphoning 30 gallons of diesel... well lets just say the wife won't want to kiss me for a while. Burp! EEEW whats that smell, Diesel fuel honey.

i cant get rid or that first quote any way that kinda stuff doesnt bother my wife she just locks me out of the house and gives me the look:nono:. i am good at taking the tank off. had to do it twice when i installed mine. someone forgot to attach a clamp properly.

[RJC2]

You know I took mine off twice too.

I'll get stinky in the morning. And see what is wrong.

--- Update to the previous post...

Well today the saga continues.

I called Air Dog to see what they suggested before starting. The tech basically said he didn't think it was bad fuel but possibly the draw straw, or the gauge. He told me to take the feed line from the tank off and put it in a bucket and see if things normalized. If it didn't he said to replace the filters. However, he did say that hooking the fuel pressure gauge in at the factory filter (as I have it) with a needle valve isn't a good idea. He told me to relocate the line for the fuel pressure gauge to the 1/8" port in the top of the Air Dog. He said this will give a more accurate reading of what the pump is putting out.

SO, I straight lined the pump to a can of about 1.5 gallons of fuel and bumped the starter. 2 psi. of pressure. It just about emptied the can in the 25 seconds that the pump ran (pumping it back to the fuel tank) which indicates to me that the pump was pumping enough pressure to open the valve in the VP44, pumping it back to the tank.

Next, I replaced all three filters. Hit the starter again, 2 psi. Another $50 wasted on filters.

I then tried to call Air Dog back, but they must quit early on Friday, so no help there.

The only thing I know to do now is to go to Advance Auto parts and get a Fuel Pressure Test Gauge and hook it up to the line that hooks to the islolator for the trucks fuel pressure gauge as I don't have a spot on the VP44 anymore to test it.

Any thought are appreciated.

[dripley]

thinking outloud, if you are still using the oe filoter basket and that filter clogs you would never know the pressure beyond that filter. say your gauge is reading 15 psi at the AD and the oe filter clogs you would still be reading good pressure but your fuel would just be returning to the tank and very little would be getting to the vp. it seems to me you would want to know what the pressure is after all of the filters.is your draw straw cut on an angle or have notches or something to where it wont suck down to the bottom of the tank?when you pumped the fuel from the bucket straight into the tank i dont think you would have much pressure beings the only thing you are pumping against is the fuel line. ther is nothing to build pressure against. it does sound like you have flow. like a fire hose, with the nozzle on the end you have alot of pressure and less flow(gpm), take the nozzle off and you have less pressure but increased flow. have you connected it back up to the truck to see what your gauge reads? when i put my big line kit in i installed the tapped 90 so i could put a test gauge on it if i needed to. not sure if i will have to reprime the system after openig since ther is no scharder valve in it now and it does dribble fuel when you uncap it. you caught me driving home from tenn. ill keep thinking and maybe some one else will chime in and help us.Dave

[RJC2]

Thanks Dave, I agree with you that I would rather see what the pressure is out near the VP44, where it matters. For whatever reason he didn't like that set up at all. I told him I kept the stock housing for the fuel heater, he said that it was pretty much worthless and I would have been better off without it.I am not sure I follow you about the bucket test. The pump was drawing fuel from a fuel can as opposed to the tank. Same fuel either way, just feeding from a different location. This let me know if the draw straw has a problem. It seemed to be fine. The draw straw in my truck is cut at an angle, inside the cup. As per your instructions I drilled two 9/16" holes about 2" up from the bottom of the cup. Eric at Vulcan said that the number of holes really didn't matter(he recommended one 1/2" hole). All I know is that mine starts drawing air on steep grades at just under 1/4 tank. In my untrained and ingorant opinion, these trucks need a sump, and a good sized one. The cup us sucked dry in seconds. When I watched how it sucked that diesel can dry in 25 seconds I realized that the cup isn't much help in there. I am going to try the fuel pressure test gauge in the morning. This thing has run me broke lately. But better days are coming...

[dripley]

i kept my oe canister for the fuel heater and the fws. not sure how that is better than not using its just how i wanted to do it. i think we are in the minority of people who use these types of pumps. any way that is a personal decision and i like it.just to make sure i got this right. you took the draw straw out of the tank connected to the fuel line and placed the ds into the budket of fuel. you took the line feeding the vp and place it back into the fuel tank so the fuel would have somewhere to go. if i am not right let me know.with just the open end of the hose going ito the tank you have no retriction on the end of it,ie the vp, and you can pump alot of fuel with no restiction at a lower pressure than you can with the vp on the other end. on my pump i am idleing at 20psi to the pump. my pump has the capacity of 165gph wich the vp does not need at idle and it returns some of that fuel thru the return line. i am alittle cloudy on this part.the AD also returns fuel to the tank thru its return. the air conaminated fuel and i believe exces fuel form the pump also. ther are some guy here that know how these pumps work better than me. i blieve ther should have been a diagram with your install instuctions that might wxplain that better tha i.as far as the ds picking up fuel ffom the basket. min differs from yours in the style of the basket and the return fuel. i have an intak fuel basket, my pickup is in there, but also the return from the engine and the return from the pump, so all of my return fuel is going straight in the basket to the pick up and i can suck my tank almost dry. that was part of the kit to replace the intank pump that came with the adII. seems to me there ought tobe a way to open your basket up and let more fuel in. does the engine return line feed into the basket like mine?i understand about buckson the truck. rebuilt the whole front end, 2 ecms, a vp,an AD, a nv 5600, and injectors. in the past 20 months. idrove for just over 8 years and not any problems just maintenance. apparently not quite often enogh. but i plan on driving this until i am sitting in a pile of debris, but the cummins and the fuel tank will still be there running like a scalded dog.

[RJC2]

What I did was to take off the infeed line from the fuel tank to the Air Dog. I had some Air Dog fuel line left over from the install and I had bought an extra fitting that fit the intake port on the pump, so I put the fitting on the exra pipe which made a new intake line about 3' long. I didn't have to unhook anything from the fuel tank. I put the 3' line into a fuel can with 1.5 gallons of fuel and bumped the starter. I got 2 psi. Then replaced all the filters and still 2 psi. So the way I see it, it has to be one of three things; (1) the Air Dog pump, (2) bad gauge, or (3) an obstruction in the line from the Air Dog to the factory canister filter. I have a Vulcan 3/8" rubber line coming off the needle valve at the bottom of the factory canister filter. It hooks up to the islolator, and that hooks to the plastic line to the gauge in the truck. I will unhook the vulcan rubber line at the isolator (leaving the isolator out) and hook up the test gauge there to test the pressure at the factory cansister. I bought a fuel pressure test gauge early this morning and got home with big hopes to see what the results would be, but I was called upon by a friend in need which took all day, so I will have to wait until Monday to see what the pressure reads. The truck does still start and run, but I am not going to drive it until this is resolved.The return coming back to the tank comes into the bucket in the tank. (my truck had the OE intank pump)Thanks for taking your time to help me, it is appreciated.

[dripley]

i did misunderstand how you did the test with the bucket. i thought you had disconnceted the intake to the ad and the supply to the vp and let the supply to the vp pump back into the tank. thats where i came up with the unresticted flow i was talking about. ithought you had that line just stuck in the tank free flowing.

let us knowhow it goes.

--- Update to the previous post...

i did misunderstand how you did the test with the bucket. i thought you had disconnceted the intake to the ad and the supply to the vp and let the supply to the vp pump back into the tank. thats where i came up with the unresticted flow i was talking about. ithought you had that line just stuck in the tank free flowing.<BR> let us knowhow it goes.

[RJC2]

Okay, I found the problem. It was the Isolator. The diaphram had turned inside out. For the life of me I can't figure out how this happened. No leaks in the lines, everything bled well. And it happened pretty fast too. In about 25 minutes of driving it went from 16.5 psi to 2psi. I followed the installation instruction to a tee.Now what was my lesson learned here? Listen to Moparman. He warned me about the isolator and what the chances were of it going bad or just screwing up. It lasted about 5 or 6 weeks. It cost me about an extra $90 for the isolator, then the Vulcan line to run to it (I can't remember how much that was) around $20. Then figure in the cost of a set of fuel filters ($50) and the truck being down. Yeah, I learned a little lesson. Now I have it hard lined into the gauge with air brake line as "someone" suggested in the beginning. Instead of 16.5 psi it now reads 17.5 psi. The wall thickness is much better on the air brake line and it is a whole lot tougher than the clear line that comes with the Isspro gauge. The clear line is so easy to kink, the air brake line would be hard to kink.So when the salesman says "I wouldn't be even THINK about installing a fuel pressure gauge without an isolator" it's a sales pitch that the gauge manufacturers must give them to sell a whole lot of islolators. As for my isolator,,, It is now a real expensive paper weight on my workbench. A reminder.Go ahead Mike, I deserve it...

[dripley]

RJ glad you got her running. did you have the needle valve almost closed. mine is so shut it would only drip fuel i belive. mine is connected with that samll nylon line and works fine.(for now anyway, mike aiint never gonna let me forget if it stays on long enough to blow). the polyon looks to be the best for sure.those $90 isolators is why i used a mech right into the cab. i dont see why you could not save the filters you swapped if you can seal them up in a ziplock for storage until you need replacements. anyway iam :hyper: for you. by the way ia m patriot blue also.Old blue rules

[RJC2]

Dave, I have the needle valve closed a good bit. I watched Mikes video on how to adjust it and noticed that his gauge needle took about 3-4 seconds to get to full pressure when it was adjusted right, so that is how I have tried to adjust mine. It is at the point where it still shows differences in the pressure readings, but is just a hair from being completely shut.Finding that air brake line was a bugger. I finally did find it, right where Mike said it would be, at Napa. I had checked with every Napa in my area, and some farther away stores without any luck. Then I called one store that I had called before (closest to me) and the guy said "oh yeah, we have it, it's somewhere in the back" I kept refering to it being Polyon and his line was a different brand so I guess it threw him off. The guy had a good bit of it actually. It is the 1/8" size. Even the Kenworth dealership didn't have this size. FYI, I bought 10 feet of it and only had about 2 feet left over. I did leave it a little long and just curled it up in the dash behind the gauge so I could reach the gauge out of the passenger side door if I had to bleed or cut it. Wifey gets ill smelling diesel so I didn't want to chance spilling any in the cab. It worked out well. I just wish I had checked the gauge first. I wouldn't of had to take the diesel bath fooling around checking everything else before going to the gauge. My clothes are still soaking in the sink in the basement to cut the diesel smell before washing them. If you can't find any air brake line down there let me know and I will ship you some. Bob

[dripley]

i had the same problem with the polyon thats why i used the stuff i did. guess i will start looking again. i would hate for it to bust. i also drilled a small hole in my a pillar mount just below the gauge so i could tell if it was leaking. good thing i did because i did leak and i had to take it back off and retighten the line.

[RJC2]

I have left my bezel off and gauge unmounted for a few days for just that reason. The bezel has epoxy drying on it (again) every time I take it off I get another crack and another tab breaks off. Real quality stuff, that interior plastic they use on these trucks. Maybe after they have been in business a for a few years they will get that kind of thing ironed out.

[dripley]

i am afraid to take my bezel off for fear of it being a pile of broken pieces when i do. i have no idea what is keeping my dash in place. it almost looks like a jig saw puzzle. kinda like a chicken has been pecking on it:lmao:.