Engine/Transmission (1998.5 - 2002) Another VP44 bites the dust!

[piperpilot3tk]

I just bought my 02 about six weeks ago and it was completely stock with 128000 miles and original lift pump and injection pump. I knew it needed a fuel gauge installed and could use a new lift pump just because of the age and mileage. So I ordered a fuel gauge and Fass LP, but the Fass went back order for two weeks. So two weeks go by and the new pump shows up, then two days later I get code 0216 and truck ran like crap even after resetting the ECM to clear the limp mode. I checked the lift pump and it was not making much pressure and was making strange noises. So I installed the new LP and the truck ran ok but was still setting code 0216, so I ordered a remanufactured IP from DAP. Took a little over two and a half hours to install and the truck runs great. One thing I noticed while installing the new IP was that the overflow valve has a small orifice about .025-.030" up stream of the pressure relief ball valve that allows fuel to constantly flow to return. I have read hundreds of times where guys swear you have to have something like 14-16 PSI to hold the overflow valve open to get enough fuel flow through the IP to cool it or a failure will be imminent. After seeing this orifice in the overflow valve I am not sure I buy the high pressure LP theory.

 

[JR]

From reading your other post it certainly has been an expensive New Year!

The whole theory of maintaining higher fuel pressure is controversial, but I have to disagree on your theory with the overflow valve. That tiny orifice is merely a bleed hole to allow any entrapped air out of the chamber to prevent damage to the VP, there could never be enough volume passing through such a small opening to move any tangible amount of fuel...that would be like assuming the bleed hole on a thermostat allows sufficient coolant to circulate to keep an engine cool...without the thermostat opening properly (or the overflow on the VP) things are going to get rather warm and stale. I think the biggest improvements made to the VP44 compared to earlier pumps are the refinements of certain internal components like the steel housing, the rotor and distributor, as well as probably some changes in soldering practices in the computers, that have made for a more reliable pump, but I believe there is at least some merit to the idea of maintaining higher pressures than the oem pumps are capable of. Just my opinion of course, I certainly am no certified Bosch technician

 

[piperpilot3tk]

Well I would not say that the bleed hole does not move any tangible amount of fuel. If you were to hard wire the lift pump and run some fuel at the stock lift pump pressure through that orifice I bet you could fill a coke can in a couple of minutes flat. I would even bet that while cruising on the road under steady throttle the engine does not even use as much as bypasses through the orifice alone. I just don't get why my IP lasted as long as it did with the stock LP if VP44 death is imminent unless you have a huge aftermarket lift pump holding an overflow check valve open. Another point I find interesting is that some guys have tried to measure return flow from the overflow valve using just a high pressure LP, but I have never seen where anyone has tried to measure fuel return from the IP with a stock LP running at cruise RPM. Maybe in a stock set up the overflow valve will open above a certain RPM due to the vane pump inside of the VP44?