Engine/Transmission (1998.5 - 2002) yet another fuel pressure?

[jelvington]

I installed new injectors, EZ w/boost elbow and gauges a couple of weeks ago. How much fuel pressure should I be getting? I installed the gauge at the schrader valve on the VP44 using the hose from Geno's to the isolator. I am getting 7-8psi at 65mph and almost 10psi at idle. I have not tested WOT.

 

[jmtandem]

fuel pressure

check almost any site on this and the concensus is that a new fuel pump should put out about 14 or more tested pre filter at idle, and at least 12 at cruise (65 or so level ground not towing). Numbers substantially less than those are probably cause for concern.

 

[WadePatton]

WOT is all that matters.



So long as you have pressure at idle and cruise. Just because you get a 12 or a 14 or a 10 at idle/cruise really doesn't tell you much, UNLESS you see a steady decrease over a period of time, then your pump is going TU. But pumps vary out of the box--as do gauges, so don't sweat a pound or two, especially at low demand.



The test of the setup is WOT, max fuel, and high RPM. At that point I, personally, am comfortable if I have 4 or 5 psi. It is recommended to have 8.



After modding my lines I now have almost 8psi at WFO, 36#, 400+ HP, 3000 RPM. (Before that BOMB, I got zero quite often. )



Happy Camper.

 

[jmadden]

I'm waiting on some info on acceptable pressures from Cummins. They indicated my VP44 died of fuel starvation and I had the following pressures:



Idle: 13psi

70mph: 9psi

WOT: 6psi.



At least one of those numbers must not be high enough or fuel starvation perhaps wasn't the cause of the failure.



jm

 

[plongson]

"Starvation", means that the the VP-44 is needing more fuel than the LP can supply... . The fact that the VP-44 supply side, had POSITIVE PRESSURE means that there was more fuel than it required. Thus it was not starving. I believe in the latest theory, that VOLUME must be considered as well as PRESSURE. If the VP-44 had 100 psi @ 100gpm on its suction side, it would still only use as much as the engine required. BUT if they went to "0"psi and "0"gpm... LOOK OUT...

 

[jmtandem]

starvation?

jmadden,



You might ask for clarification on the term 'starvation'. The lift pump puts out the same pressure all the time it is running. When at idle, half throttle or full throttle the pressure is the same, the reason pressure reads lower with more throttle is because the engine is using more fuel, the volume changes. Unless the engine was using more fuel than the pump could supply or the filter is very restrictive then how can the injection pump be starved? A fuel pressure reading of five or six at full throttle is still sending fuel to the injection pump.

 

[jmadden]

here's the latest from Cummins:



"On ISB engines, the lift pump does not start operating with the key switch on until the engine is bump cranked. Then it starts working for 30 seconds and then shuts down by itself. During 30 seconds of running, it primes the fuel system. Pressure during this running period should be around 13 to 15psi and during cranking, the pressure should not drop down more than 8psi. We have seen in the past that even if the pressure are found to be within specs, priming pumps due to internal check valve and excessively worn out pump impellers, that it creates fuel

spikes which create and pump air into the fuel system, which leads to the major problem in the VP44. There is no fool proof methods to check the internal condition of the priming pump or to check air created by the priming pump. "



jm

 

[Steve Campbell]

"There is no fool proof methods to check the internal condition of the priming pump o

I do not know if my fix is fool proof, but I put a tee in the return line and a valve and hose out of the pre-filter plug on my 99 and return a "small" amout of pre-filterd fuel (which includes most of the air) back to the tank.