I have been running the Walbro 392 from GDP for about a year now with no issues until yesterday. At a hard takeoff FP dropped to ZERO, this is the reading off my Juice. I usually run at 19-16 maybe 15 at WOT. I just changed the filter about 2000mi ago. And it has only been getting down to low 30's at the coldest, I run plenty of Powerservice per tank so I know its not a gel issue. After it went to 0 for a second it came back up to 18ish cruising around town it was erractic one sec. it 18,17,7,14,21,16 and so on. I took the pump off, cleaned all connections, ckd. my pump prefilter, took the line of the inlet of the pump to look in there, everything appeared fine so I reassembled and drove, ran fine @WOT never saw less than 15. The truck sat for about 5 hours, went to take off.....same thing as I accelerated pressure went down to 7 or so, then pops up even as im still giving it the skinny pedal. Drove about 20 miles on that trip it only did it to me right at the start. Parked the truck took the FF apart, nothing noticeably wrong, drove about 100 mi, ran great no FP issues. This morning went to take off and on accel. it still dropped to about 7 or so then came back up to normal. I really dont think its a sending unit issue because it drops so drastically when I accel. Im thinking maybe a bypass issue? I have the preset one that comes with the kit, i know there isnt much to it to go wrong but I dont know what else it could be, I hope its not the pump taking a dump--could it be? Anyideas please?

 

It is 100% a bypass issue

Pull the regulator off of the frame, or where ever you decided to put it. pull it apart, and usually you will see a tiny bit of crap in there. That tiny bit is enough to hang the piston inside the regulator.

When I did mine, as well as a couple others, I took the time to deburr the bypass piston holes as well, something that isn't done by the machine that punches these things out. These pump systems are great, work through the best and worst of weather, hot and cold, rain and snow... Kind of like the mailman, without the union.

This said, I have dealt with several of these pistons hanging like this, and it is not a big deal to repair. It will hang open giving 0 psi, then next hting you know, it hangs shut and you get 30 - 40 psi, nasty situation, neither is good for your VP pump.

After cleaning and deburring, there have been no issues at all with the pressure fluctuations.

Good luck with it.

 

Thanks alot for the info, I will take a look at the bypass as soon as I can, I did find it odd that today I would got 21 psi for a moment which I have never gotten before, but then it would dip back down. Thanks alot!