CTDboy

This is one of my first posts here, but i have been lurking in the shadows for about 3 months now since i got my truck, reading and learning. Now i have a problem.

Ok boys, put your thinking caps on for this one. I started by changing my fuel filter cause I am not having the best of fuel milage (13-14mpg). I could not get the system to reprime after the filter change. Eventually, the lp just stopped alltogeher when i was trying to prime the system. I ordered and installed a GDP walbro 392 kit (very nice kit by the way). Took about 3hrs and the truck started right up after priming. Drove the truck and had 15psi at moderate throttle cruzing around town with my test gauge. But, if i got on the throttle at all the engine stubbled like crazy making no power. Now, i only had a 1/4 tank of fuel at the time so i stopped and filled up to 1/2 tank. The truck drove a lot better but still studdered when on the throttle. Checked the codes; no P0216 thank god. I reset APPS. No effect. I filled up with fuel all the way and the truck drives nicely up until 65mph and 2000rpms or so, then studdering continues. I put my test gauge back on and now i am getting 12psi at idle and when i drive anywhere it drops to -7psi. Yes, negative pressure. I have checked all of the wiring and the pump is running, and there are no kniks in the fuel lines. My next thought is a fuel pickup issue in the tank. Maybe clogged pick up? HELP PLEASE!

Ram1999

That's what I was thinking as I read your post.

CTDboy

Yeah, I was hoping it would be something easier. As i just filled the tank, dropping it is not an option. So i guess i need to pull the bed off. Does anyone know if this is that difficult using and engine hoist or a few extra hands?

LonestarCTD

It definitely sounds like the fuel pickup in the tank. I just read a similar thread where someone had almost identical symptoms and checked the tank pickup. They found some kind of gooey substance all over the screen on the pickup and it appeared like the stuff was causing the screen to clog when pressure was applied. After removing the screen, the problem was corrected. Make sure you have a pre-filter (Fleetguard#FF5079) installed before the Walbro if you're going to remove that screen at the pickup, otherwise you could pull a lot of garbage into your new Walbro. You have to remember, the Walbro is pulling a LOT of fuel out of the tank so the pull on that screen is going to be amplified. I've been thinking of doing that to mine as well. I haven't seen a problem with it but from the way it looks, that may be the reason that the lift pumps were having a problem in the first place. Hope this helps.

CTDboy

I guess the $12.99 i spent on the fleetguard filter was money well spent. Is it ok to completely remove the screen in the pickup or should i clean it and put it back? Good time to do Vulcan draw-straw maybe?

mbfarms

Most of all the Walbro problems are one of two things. Trash in the inlet side of the pump or clogged tank module. Yes this would be a perfect time to do a draw straw, but make sure to get a good prefilter.

swmnkdinthervr

I was told that you can block the tank up in place, unfasten the tank and jack the truck high enough to access the tank...

CORed

My Walbro exhibits interesting behavior on occasion too, but never negative pressure. I have seen it pull down to 3psi when normal idle is almost 16lb and normal driving is maybe 15lb. It is really odd and I can't figure it out. Cold fuel seems to produce the highest pressures.

I replaced the pre-strainer that I ordered w/ it from GDP and it was fine, nothing in the strainer when I cut it open. I put another one in the same position. But before doing this, I blew about 20psi of air back up into the tank using the open end of the hose. (Remember to take the cap off first). I verified that it was getting voltage as well as taking the cap off and verifying it was not drawing a vacuum. All checked out OK but symptoms still happen occasionally.

So I guess it could still be something in the tank messing with the pickup tube, but whatever it is, it doesn't show up in the strainer.

My only other idea is voltage. I am running the Walbro directly off wires from the lift pump harness that I cut and spliced into. (the OEM pump is long gone). So I'm NOT running the pump off a relay setup. My theory is that it is possible the pump varies in output significantly only with minor changes in voltage, but who knows.

So your thread caught my eye. Please let us all know what you do in the tank pickup and if it solves your problem. I didn't want to drop the tank or lift the bed at this point... it's about 25* in my garage these days.

Sorry for the long post.
Steve

TNfarmboy

I run mine off a relay that gets triggered from the stock LP wires. That could be part of your problem....and don't forget grounds!

CORed

Thanks farmboy, I assume you are experiencing none of these intermittent issues with pressure drops?

Anyone else running thru a relay and experiencing NO weird problems like myself and others on this thread? Anyone running directly off the original lift pump wires withOUT a relay AND experiencing pressure drops?

Any other theories?

Steve

DSjockey

I put in the GDP 392 kit (with the recommended strainer) about 3-4 months ago, immediately went on a 2000 mi trip with the 5er, having no problems at all, 19 at idle, have not been able to pull it below 16, just going to make a protective cover/shield with some aluminum diamond plate so it doesn't take direct shots from slush and snow. Probably a silly question but have you checked for voltage at the pump while running? When you say that it's pulling a negative pressure # it makes me think that the VP is sucking the fuel. I believe that using a relay with the factory pump wiring connected to the coil is the way to go

pind

I have had the 392 setup on, with the pre filter, and the proper relay since september, about 20,000 km. No problems with fluctuating pressures, no problems with flow. this is using the stock pick up in the tank.

The pump is mounted inside the frame rail to the rear of the t-case. completely exposed, which, looking back, is probably less than intelligent, but I was in a hurry, and I'll live with my stupidity until such time as I can move it.

I would say throw a relay in, triggered by the stock wiring, and see what happens, worst case, you are out a couple bucks and an hour of your day.

Good Luck

TNfarmboy

No problems....I have not put on as many miles as DSjockey and pind.

CTDboy

Well, i dropped the tank down and cleaned what little debris there was in the in-tank filter. Tried to start truck, and no go. It will prime to 18 psi, but my gauge (electronic) registers -7 psi. the truck runs for about 15 sec after i prime it then it dies. I am running a relay powered by the stock wiring. I tested the pump while the truck was running and no power to pump. I didn't feel like chasing wires so i unplugged the stock wiring and bypassed it to an ACC source and put it on a switch. I no have a pump that runs when the truck is running (verified 12v at pump), but still 18psi at prime and -7psi when the truck is running, before it dies. I pulled the overflow valve and tested it. It does open at 14psi, but it also opens down to about 8psi as well. Hard to tell how accurate with adjusting pressure that low on my compressor. I have heard of trucks starting poorly with bad overflow valves, but never not running at all. Thoughts? Is it possible that i have air in the injector lines? I am honestly running out of ideas at this point guys. I have eliminated all of the electrical posiblities, so what is next? I would probly even take it to a mechanic at this point except there are none within 15 sec of my house. I have had this truck (1st diesel) for about 3 months now and it is really starting to dissapoint me. Sorry for the long post.

RickCJ

If your pump is running but not pumping! I'd start with another pump. Ever hear of FASS?