Engine died

[PMalin]

Not sure if you are running stock or have any power modifications. Either way from what I recall reading here (and I believe in the FSM?) feed pressures less than 10# are not good for the life of the VP. I also read here the VP doesn't like more than 22.5# head (feed) pressure. I set my regulator at 20# and checked accuracy to the in-cab gauge with a mechanical gauge, spot on. With my Edge set at kill and wide open throttle I've never seen less than 18#. Most folks run around 16#.

Engine is Stock...

 

[petersonj]

I will probably be challenged here, but the following is my perception of how the VP44 fuel system works. Some of this comes from many hours of research over the years reading many solid documentations of return flow testing of the VP44 fuel system. The rest comes from my own experiences and VP44 testing with my truck, and my background in fluid power.

I was thinking that this carter pump should provide plenty of pressure,

Pumps do not provide pressure. They provide flow. When flow meets resistance, then pressure is generated. When a lift pump output volume (flow) exceeds the input volume (flow) of the VP44's internal fixed displacement vane pump, then the pressure will rise and continue rise until the operating pressure of the pressure regulating valve inside the lift pump has been reached and allows the excess flow to be diverted back to the suction side of the said lift pump.

In a nutshell. The fixed displacement vane pump inside the VP44 provides the flow (pressure regulated from 116 - 319 psi) to all internal operating components, flow to the injectors, and flow to the 14 psi overflow valve to return lots of fuel back to the fuel tank. The lift pump has nothing to do with this. The primary purpose of the lift pump is to provide more flow than the VP44 injection pump can consume under any operating condition. That's all. Nothing else.

From the 2002 FSM - The fuel volume of the transfer pump will always provide more fuel than the fuel injection pump requires. This will be why you always see a positive pressure on your fuel pressure gauge.

From Bosch - The first thing the incoming fuel sees in the VP44 is a vane-type fuel pump (called by Bosch the ‘Internal Fuel Pump’) which raises the pressure to “8 – 22 bar (116-319 PSI) depending on the application and RPM” (direct quote from VP44 Service Manual and Bosch Fuel Injection Pump Manual).

@Joe Mc mentions, "feed pressures less than 10# are not good for the life of the VP".

2002 FSM states, "(6) Start engine and record fuel pressure. Pressure should be a minimum of 69 kPa (10 psi) at idle speed.

What the FSM does not state and also what Bosch kept quiet about for years was that the lift pump pressure was not nearly as critical as was believed at the time. Early on, the real problems were inside the VP44 injection pump. Things like: rotors that did not get deburred, plastic diaphragms (instead of steel) for dampening pulses, plastic parts in timing piston assemblies, poor solder connections in the PSG, etc. Bosch quietly fixed those issues and the Bosch certified remanufactured VP44 injection pumps came out with the improvements automatically.

My own personal experience supports this. A bit of history – the first VP44 injection pump on my truck failed (code 0216) and was replaced under warranty along with the engine block-mounted lift pump which was also replaced under warranty with an in-tank lift pump in August of 2005 at 87,000 miles. At first, I was disappointed that I received a remanufactured VP44 injection pump, but as I learned more about VP44 failures, I was very happy that I received a remanufactured pump.

The old block-mounted lift pump was still providing 12 psi at idle and 7 psi at wide open throttle when it was replaced. The new in-tank lift pump provided 6 psi at idle and 3 psi at wide open throttle. I ran that lift pump for 164,000 miles. Some would say that low fuel pressure like this would trash the VP44. Not the case at all. In April of 2016 at 251,000 miles on the truck, I removed the in-tank lift pump and installed a used FASS DRP-02 frame mounted lift pump. The in-tank lift pump was still working fine – I just wanted the lift pump to be easily accessible if it failed on a road trip. The FASS lift pump provides 12 psi at idle and 6 psi at wide open throttle.

Currently, there is approximately 106,000 miles logged on the used FASS DRP-02 lift pump. The current replaced VP44 has logged over 273,000 miles. I am not concerned about low fuel pressure.

So, the thing is my pressure may be more a result of my VP44 (overflow/return spring) or whatever it is that regulates the pressure, being the reason I do not see a higher pressure than this???

It has nothing to do with the VP44 injection pump. It has all to do with rated flow and pressure setting on the lift pump. Plus there are other factors that muddle with the expectation of a particular lift pump. Being that it is an electric pump, wiring size and good connections are key to having proper voltage at the lift pump. Voltage drop reduces flow performance. As pressure rises, the lift pump speed slows resulting in lower flow output. Usually when these pumps are advertised, a flow rate will be given, but a flow rate at a specific pressure is not given. So, in the end it will be difficult to know exactly what you are getting in terms of flow. But, it really doesn't matter anyway - as long as there is a positive pressure at the inlet of the VP44, the VP44 will be fine.

I would not worry over your fuel pump pressure. But, you can if you want to.

- John

 

[PMalin]

Well, I went ahead and installed a check valve just ahead of my relocated lift pump. Installed a Fuelab 71702 and I called them prior to doing this and asked what is the pressure that it takes to activate this (open it up to flow) in the direction of flow. He said it takes about 2 psi (They have a spring to force it closed that has to be overcome) . Then I discussed how the vp44 basically functions as a regulator for this by limiting the resulting pressure and returning excess flow to the tank. He replied then, that I should see no drop in my pressure as a result of this (2 psi) thing. Due to the Carter pump being able to pressurize and flow in excess of this and then it will be essentially regulated at the VP44. Next step cut the line and installed it. I didnt see much pressure drop but maybe 1 psi or less so far at idle. Road test tomorrow, and I think it will be slightly lower than earlier values without the checkvalve. But will it give me an easy startup??? Mr. Pertersonj I appreciate your writeup on the details above.

Basically my idea of the lift pump is to provide sufficient combination of flow and or pressure to maintain some positive pressure at the VP44 under all conditions to (supply it with fuel) Excess is routed back to the tank. Some talk of the need to cool the VP44 with some of this flow as well. I have found recently that without a functional lift pump, the engine dies. I suppose an extremely weak lift pump may still allow things to work, but your getting close to the failure point if that be the case. Some say that can damage the VP44, likely due to minimal cooling effect of the flowing fuel through it.

 

[petersonj]

Well, I went ahead and installed a check valve just ahead of my relocated lift pump

In terms of fuel flow direction, is the check valve installed upstream or downstream of the lift pump? Suction side or discharge side of the lift pump? Hopefully it is on the discharge side. If I am understanding correctly, you have installed a dedicated fuel return line from the lift pump. What is the approximate rated flow for the lift pump?

Basically my idea of the lift pump is to provide sufficient combination of flow and or pressure to maintain some positive pressure at the VP44 under all conditions to (supply it with fuel)

This is a good idea.

I have found recently that without a functional lift pump, the engine dies.

This would mean that when your lift pump became dysfunctional, the fuel passageway became severely restricted or completely blocked. If the passageway would have remained open, the VP44 internal vane pump would have continued to draw fuel into the VP44 and the engine would not have missed a beat and full return fuel flow would not have been interrupted. To illustrate this, last summer I performed some fuel return flow tests. With the assistance of a friend, we conducted flow tests into a measured container. Test #3 and #4 had a fuel line routed around the lift pump (fuel transfer pump).

Test #1: engine at idle, fuel transfer pump operating - .5 gallons pumped in 92 seconds
Test #2: engine at idle, fuel transfer pump operating - .5 gallons pumped in 94 seconds

Average fuel pumped is .5 gallons in 93 seconds = .3225 gpm rounded to .32 gpm or 19.35 gph

Test #3: engine at idle, fuel transfer pump disabled - .5 gallons pumped in 93 seconds
Test #4: engine at idle, fuel transfer pump disabled - .5 gallons pumped in 95 seconds

Average fuel pumped is .5 gallons in 94 seconds = .3191 gpm rounded to .32 gpm or 19.35 gph

Note that the return flow from the VP44 is virtually the same whether or not the lift pump is operational. This clearly shows that the internal vane pump is doing the work, not the lift pump. I performed one other test. Since I am certain that it is the internal vane pump that does all of the work, I disabled the lift pump and drove my truck to town and back – a 25 mile round trip. I accelerated hard and held 30 psi boost several times. I restarted the truck several times while running errands. The engine never stumbled and continued to deliver the power it always does. Of course, I reconnected power to the lift pump when I arrived home.

Let us know how you test drive turns out.

- John

 

[PMalin]

Well the truck has sit several hours yesterday and overnight. Testing to see if the checkvalve helps me get a standard routine startup. Yes it did!!! No bump starter routine to pump fuel ahead of crankup. Just rotate key 1st position, 2nd position and wait for warmup cycle, then crank to start and she fired up. No accelerator input needed to assist. Now for the updated fuel pressures since the checkvalve install. Some were recorded yesterday some today. Bump starter = 9 psi, Truck Idle = 7 psi, 70mph 5 to 6 psi, Accelerate normal 5 psi, Accelerate hard 4 psi. In general the readings dropped 1 psi since install of the checkvalve mentioned. But it gave me the benefit of a normal startup without hassle.

Thanks for the replies to everyone.
I dont know what else there is to report on this now.
Good luck ...