Flyinb1

Ok...Last winter i posted about having fp problems and at that time i thought it could be partal ice problems in the fuel, it cleard up with the warm weather so maybe it was. I have a walbro pump just ahead of the tank, a mechanical FP gauge, idles at 15 psi, drops to about 12 psi wot normally. Yesterday i was about 70 miles from home when 0 fuel pressure..pull over stop motor, bump starter..15psi...great...head down the road a couple miles...fuel pressure goes to 0 again...stop/ restart...got pressure again, start to go...pressure goes to 0. This hapened a half dozon times. I have a spare Walbro so i replace it on the side of the road...Great..pressure back to normal, head down the road with no pressure loss at all...great. Drive 70 miles home with solid fp, stop at my gate and yikes...0 pf again. stop motor/ restart pressure back, start to go and pressure drops to 0. Trying to figure out how changing the pump would fix the problem perfect for 70 miles then back to same problem.

pind

if you have the bypass regulator, that could be your problem. it doesn't take much to make the pistin in there hang up and give you 0 pressure, or really high pressure, depending where it sticks.

Just something to check

Flyinb1

Thanks...After another cup o coffee that was one thing i was going to check as i do have a regulator, just cant figure why it worked for 70 miles after changing pumps...maybe moving the bypass around while changing the pump lossened it up a bit.

Flyinb1

Update on what i've done so far...Took the bypass regulator apart and checked it out, has a spring and nylon type round ball, everything looks good, put back togather, same problem. Drop tank, no crud and everything looks normal in there. put a hose right to my Walbro pump and into a 5 gallon can of fuel (bypassing tank all togather) Start truck, good pressure for a few minutes then drops to 0. So seems from the pump back to tank is not the problem. Change fuel filter, no go. I am down to two possabilitys...My Walbro pump craped out then my second Walbro craped out after only 70 miles...I thought they where good pumps? Or could the relef valve on the return line banjo fitting of the VP be the problem?

Bruce

bent valves

Another possibility might be an electrical problem where the power to the pump is intermittent. You have probably wired the Walbro using a relay triggered from the ECM. Be sure all is well with the connections.

To test to see if it is the Walbro, unhook the relay and connect it up directly to the battery. If it only makes pressure for a couple of minutes now, the pump must be bad. Divide and conquer.

Flyinb1

Dave..Thanks for the imput...Yes that is how i hooked up my pump. I did hook up my DVM to the pump teminals and watched the voltage as it lost pressure and voltage to the pump stayed 12~13 volts. Just cant understand why the pump works (and holds pressure) for a few minutes every time the truck is started then slowly drops to 0.

bent valves

If the pressure slowly drops off to 0 as you say, either the pump motor speed slows and stops or there is a restriction that reoccurs at the inlet or outlet. Having 2 pumps fail in the same way is unusual to say the least.

In your tests can you hear the pump slow down and does the pump current increase or decrease? If the pump remains running, I wonder if there is a flap of rubber inside a damaged hose that is acting like a check valve. This may increase the current flow to the pump if the output is restricted or decrease the current flow if the input is restricted. Try connecting your DVM in series with one pump lead and switch to a 10 amp scale.

VADSLRAM

You checked the voltage but did you check the pump itself? hand on to see if it's still running, when the pressure drops does the pump speed up (air) or bog down (clog).
Seems to me like somewhere in the line is a restriction that settled back when you changed the pump.
Many moons back I was driving cross country in a 72 Coupe DeVille and right outside Flagstaff it wouldn't go over 35. Idled great started fine and revved normal but it wouldn't do highway speed. 3 days and a lot of $$ in diagnostics later they found that inside my muffler a piece had broken off and at sustained high gas flow (highway speed) it would flip up and block the output..........
Maybe it's something like that in the fuel system? just sneaky enough to clog it until you shutdown then it falls back and waits.

Flyinb1

I have some time this am so i plan to check the hose forward the pump to the fuel filter to see if there is any flaps of hose or anything like VADSLRAM mentioned as that has crossed my mind as well. And no i havent checked the pump other than having voltage to it as my hearing is bad i cant hear it run with the engine on anyway :-)

Flyinb1

OK...I did a test a bit ago. I took the return line off the filler neck that comes out of the bypass valve i installed just ahead of the pump on a tee. Put the return line in a can and started the truck, when i had good fuel pressure very little fuel came out, as the pressure dropped more fuel came out...Ah ha...a blockage in the supply line between the bypass valve and the fuel filter...replaced the line from pump to filter...no go...still same problem. The only thing i can think of now is the valve in the return line of the vp44 (banjo fitting) is sticking open

bent valves

I will guarantee you it is not the valve on the VP causing the problem. Many people believe this spillback valve is responsible for controlling the lift pump pressure. It is not.

Let me try to understand your plumbing. Fuel coming from the tank goes to the Walbro pump and next to the tee. One side of the tee goes to the fuel filter and the other side goes to the bypass valve. The bypass dumps fuel back into the tank fill neck or the can in your test. Is your fuel pressure gauge connected on the output side of the fuel filter? It should be.

If my guess of your plumbing is correct, your bypass valve is receiving unfiltered fuel. Could trash in the fuel be keeping the bypass valve open? Moving the bypass downstream, after the fuel filter might help if it is dirty fuel. This will also keep the pressure constant for the VP as the fuel filter starts to clog.

It appears that there is no problem with the Walbro pump since fuel volume increases as the pressure drops. I’m going to agree with pind, that something is going on with your bypass valve

Flyinb1

Glad you believe that the VP valve is no problem as i took it off and it seems to be fine so i also decided it wasen't the problem. I have already taken the bypass valve apart and it is fine as well. I do have a filter before the pump and bypass valve. This is where i got the Walbro setup http://wideopendiesel.com/page8.html I am now wondering if it could be the fuel pump and my luck is so bad that i had two Walbros go bad back to back? With the truck running and 15psi fuel pressure how much fuel should come out of a 3/8" return line? It was barely running out. When the pressure started to drop more came out (maybe the bypass opened up) and i was thinking it was a blockage.

bent valves

OK, I went to the link you provided and see that you have a filter installed before the Walbro also the bypass regulator is placed right after the pump not after the stock fuel filter. I also discovered that one failure mechanism of the Walbro pump is that if run dry the plastic gerotor pump gears will melt.. Is it possible that your pump was run dry? As you can probably tell I am running out of ideas.

Flyinb1

I am running out of ideas as well. I dont think the pump has ever run dry as the truck hasent quit running with this pump. When this problem started i was on the road and noticed fuel pressure at 0 so i pulled over as the truck was sputtering, i figured i had crap in the fuel so i cleaned the prefilter and drove another 10 miles then it happened again after doing this about 3 more times with the distance getting less between stops untill it would only hold pressure fo a couple minutes. As it turns out cleaning the filter had nothing to do with getting the pressure to come back. Just shutting down for a few minutes and restarting would allow the pressure to come back up for a while. The only thing i did that "fixed" the problem was when i put my spare new pump on. I then drove 70 miles home with no problem. right at my gate it started all over again. Looks like the next step is to get another pump and try that.

Bruce

nitrousn

Are you sure the tank is clean and the suction screen is not plugged? You could have a loss of supply on the suction side of the pump.