Sixpack73

I just installed my walbro system about 4 weeks ago, and just noticed yesterday that when I hammer the throttle, my pressure drops from about 24psi down to 0 psi. It does recover in about 2-3 seconds though when I let up.

I have my smarty on 2 right now, and the quad on level 1, but it also does it with the quad completely off.

I've got maybe 4k to 5k miles since the install, and I just changed the fuel filter thinking that might have been the cause, but still no dice.

the only other things i can think of are that the inline strainer is clogged already (seems awful soon for that), maybe a hose is still pinched somewhere, or my pump isn't keeping up.

what do you guys think? whats the easiest way to troubleshoot?

jrussell

Were you low on fuel when this happened? A couple of people recently said they were having trouble with the GDP pickup when lower than 1/4 tank.

Sixpack73

no, 3/4 of a tank, but mine has the same symptoms as that other thread when it gets below 1/4 tank.

I guess i'm just looking for a nod that i'm troubleshooting in the right direction. i cant imagine the strainer being clogged already. Wondering if I have a bad pump or something. I'm pretty sure the lines don't have any kinks in them or pinches anywhere. i'll have to wait until this weekend to get under there and mess with it.

might try to find a shut-off valve while i'm at it because it makes a mess everytime i have to pull one of the lines loose.

deezilpwr

you could have a injector by-passing fuel causing a sudden drop in fuel pressure, is your truck hard to start?do you have the filter pointing in the right direction?(walbro)..does your truck do any missing or popping when this occurs? how do you have your gauge hooked up? if its not missing, run it like you stole it, if it is it still wont hurt to make it miss, the important pressure is at the rail, just because your primary pressure is low does not mean your cp3 is. that can your filter is in can sink 1/2 way down at wide open throtle(wot), that will cause a drop in primary fuel press. but your cp3 is still getting what it needs, YOU WILL KNOW when your cp3 runs short on fuel!!, hope3 this helps

Sixpack73

the truck starts and runs fine, it only occurs at 3/4 to WOT.

I made sure the strainer was pointed in the right direction and just changed the primary fuel filter. My fp gauge (quad) is hooked to the input of the CP3.

I've only had it miss a time or two, under WOT. It usually doesn't, but I think it must be right there on the edge of starving the cp3. As soon as I let off the throttle, pressure climbs fairly quickly back up to 24psi.

To me, its like the walbro isn't pumping enough volume through it to maintain pressure (at least 8-10 psi I would think), or i guess the strainer could be clogged up already.

I'm going to change out the strainer this weekend, but is there a way to test the pump itself? Not sure what else to try if the strainer doesn't cure it.

973604x4

check all filters and give Richard a call. He has great customer service.

My truck doesn't want to start the first time if I am below 1/2 tank. My truck died one day with 1/4 tank of fuel when I had a FASS. (i'm still using the same pick-up tube that I had with the FASS)

deezilpwr

also, you are not trying to suck fuel from your stock lift pump, did you drop your tank and as directions told you?? and is your pick up tube cut at a 45 to stop from suckin bottom of the tank?

Sixpack73

yeah, i dropped the tank and installed the pick up tube with a small 45* cut on the end of it. I'll poke around this weekend and see if I can find anything out of spec, its just irritating when stuff like this happens.

deezilpwr

if you r piick up tube is too long it could curl and partially seal that 45. you want the pick up tube around 1/2'' to 1'' from bottom to prevent sucking water, any water settles to the bottom of the tank.. i have got walbro, my 30 psi gauge is pegged, when at wot it will drop down to 20psi, they will drop, a little bit

Sixpack73

getting ready to go pick up a new strainer and try it out, but I have a feeling you are right about it being my pickup tube (or a weak pump, but leaning towards the tube).

i just really dont want to pull that tank again though.

Sixpack73

nobody had a strainer locally so as a quick test I put a straight thru splice in place of it and took her for a spin...no change, pressure still drops to 0psi at WOT.

no kinks in any hoses either, i checked for that while i was under there. so i guess that leaves the pick-up tube and/or the pump itself. guess its time to pull the tank

what would be the downside to changing the spring and shims in the bypass valve to run 30psi instead of 22 to compensate?

desertchecker

FYI i was having 6 mos worth of problems with the gdp 392 kit went through a couple of pumps had the same type of problem with the pumps eventually failing 0 psi I was getting angry and frustrated so I switched back to a fass system and guess what ......same problem ?? finally I traced the problem to a locking fuel cap that was not venting so after 6 months of aggrivation I discovered that with the fuel cap off no more problems so I am going to get a cap that vents big time ...... another expensive lesson learned !!

metal_miner

Check your GDP bypass valve. The plunger in mine had a burr on it and caused the same problems as you noted. Over time, the plunger rotated enough such that the burr caused it to hang up in the valve bore. The plunger is a soft metal so a few quick swipes with a sharp knife fixed everything.

deezilpwr

you can always slide the bed of the truck off or back on some saw horses

Sixpack73

thanks guys. I'm running the stock fuel cap, so i dunno if that would be it or not...easy enough to test out though.

interesting about the bypass valve, jsteiger, I'll have to check that out tomorrow. 'preciate the suggestion.

oh and deezil, i've never taken the bed off a truck...I assume its a few bolts in all four corners and it lifts off and/or slides backward? If its easier than pulling the tank was, it would be worth a shot. (actually pulling the tank was easy, it was getting it back up there that was a pain, guess I ain't no pro at it)