Why would my IP not bleed off through the check valve's port? Reason I say the check valve's port is because I removed the valve itself after pulling off all the other lines and checking for restrictions, of which there were none. The valve was replaced new with the pump, and it works just fine, both through its weep hole and the spring's pressure. But fuel is only trickling out of the VP44 itself after pressurizing the system, which takes a few seconds now. Before as soon as the key was turned the split second run of the LP would raise the pressure above 5 and then drop as fast as it rose. To rule the LP out, I replaced that with another under warranty, but no difference. It will make pressure in a couple of seconds, but this restricted return is slowing the process.

This all seemed to have started on a road trip of around 200 miles last week, but it's been parked since I got back. Never seen this before, but when I turned the ignition off, the pressure stayed at 15psi, off of the initial 20 at idle. Took forever to slowly drop ( like more than five minutes ) and once at two or so pounds I flipped the water drain and bled the rest. And just before I noticed this, it did take more revolutions than normal to start when at operating temps, so probably the high pressure hard starting syndrome but just didn't see it. Once running, I also noticed the dipping idle when coming to a stop that had started when I first put this IP in not more than 5k miles ago, but this time a lot heavier. I posted a question about the waving idle some time back but no response.

So I called the shop I got the pump from where it's still under warranty and one of the techs pauses after hearing I installed myself, like that's the whole problem. But then he goes into a bit about in-tank check valves and pumps and problems it could be before I could tell him about the fueling items in my sig. So only thing they can do is send it off to be checked, but I've seen some old posts here on the forums talking about if they find any additives other than diesel specific, as in the 2 cycle i've been running, that they would not warranty the pump. Any body have a similar experience, either with your pump not returning fuel or losing a warranty over 2 cycle? I was hoping it was a simple fix, but I'm fearing the worse of having to buy yet another IP

 

Surprised nobody chimed in with possibilities... but turned out it was the 2 cycle oil. Using way less than the ratio of an ounce per gallon, I was adding just under 20 oz at fill ups of 25 gallons or more. Only thing I can figure is in 5k miles, whatever's inside the pump that lets fuel pass to the return port got gunked up from the 2 cycle oil. Might be tight tolerances on a new IP? Filled up with straight diesel, added no 2 cycle oil at all, and in less than 10 minutes the FP was back to normal, plus pressure built up within a fraction of a second at first key like it used to. Think I might switch back to PS. My old 7.3L had just under 300,000 on the original IP and never had an issue with all the PS Kleen I ran through it.

 

What kind of 2 stroke oil were you running, I know it should be TCW3 ashless... I've had no problems running 1 liter of 2 stroke oil to 129 liters of fuel...

Where did you get your pump from?

 

Found out about the oil here on the boards, Wally World blue gallon jug, just like everybody else. Pump was from local injection shop, authorized Bosch dealer. They do not work on them in house, send off to Bosch builder. The manager is a really good guy, but he wasn't in that day and one of the techs answered. The techs have that "you shouldn't work on your own truck, bring it in so we can find the problem" attitude. Unless I just got the not so friendly one.

 

bump???????????????????????????????

 

With a new VP there is no free flow of fuel through it. At the input of the VP is a 4 vane pump where the vanes are spring loaded and block almost all flow if the pump is not spinning. With 100K miles on it there will be fuel leaking by the input pump and out the return fitting.

I don’t know how many times people on this forum write that the spill back valve open at about 14 psi and this is responsible for the lift pump pressure reading. IT JUST IS NOT TRUE. This misinformation originated from the way a 12 valve IP works where the spill back valve opens at about 35 psi and is used to control the internal IP pressure. The VP spill back valve has a bleed orifice to remove air and a spring loaded check valve to recycle hot fuel at high RPM.

But don’t take my word for how the VP44 works. Buy some technical books from Bosch and find out for yourself. As you might guess the misinformation on the forums is unstoppable and irritating to me. Rant over

 

So almost all flow means some flow will still pass through? I'm only asking because my initial post tells of how it trickled out. Not brand new, but only 5k miles, so still new.

So how does my FP drop as fast as it rose when the LP first cycles for a second. It only jumps to 10 psi, and drops just as fast when the pump stops. My valve is working properly so I know it is not opening. The weep hole does flow good at 10 psi though. There is no back flow going back on the supply line, as I showed by flipping the water drain and relieving pressure. Even though I do have a gerotor LP, and it does offer some back flow, the Racor pre/primary filter does not allow back flow and keeps prime behind the LP. Since I did get a trickle before, I'm pretty sure it will be flowing now if I take the valve out again. Not arguing how a VP works, because I honestly don't know, but what allows the FP to drop instantly when the LP is turned off if not back the way it came, which it can not?