got a question about the VE pump vs. the P pump...

[Forrest Nearing]

one of the things I loved about my 91. 5 was the big "BLAT" that came out of the exhaust pipe (straight pipe) when I touched the ignition key... the truck started almost instantly, and the sound that was created made many a woman and child jump halfway out of their skin!!



the first time I test drove a P-pumped truck, I thought something was wrong with it because it took a second to fire up and when I killed it, it took a couple rotations to stop... my old VE was instant start and when you killed it, it was pretty much instant stop...



talking to the fleet maintanence guy at the place I was thinking about buying the truck from, he said it was because of the difference in the pumps...



having driven a few P pumped trucks, I find them to all have the same characteristics, so now I'm wondering... what is happening inside the pump that causes the difference in how a VE truck starts/stops vs. a P truck does?



Forrest

 

[Greenleaf]

It's been some time since my college days, but if I remember right, don't all the mechanical pumps move to "full fuel" position while at cranking speed?



Therefore, I would have to site internal timing to be the variable.



-S

 

[cerberusiam]

In addition to fuel fuel on cranking the VE also advances the timing. Thats where you get the blatt and the quick start from. The KSB is responsible for advancing the cam plate as soon as pressure builds in the internal pump, holding it advanced during warmup then retarding it as the engine temps come up. The big drawback of the P pump is there is no mechanical advance mechanism in the pump. Since it is an inline pump there was no simple way to implement a mechanical advance Bosch made the decision to not try. The P pump does do fuel advance by way of changing the position of spill ports in relation to supply fuel as rpm increase but it is not as effective nor clean as the VE. Just one of the reasons the VP replaced it mid 98.

 

[brkoyle]

I sold my 1990, which fired up exactly as you describe. I now have a 1992 which has a 1996 P pump motor in it. I can crank the starter for more than 30 seconds and the motor still not fire, except if I have some pressure on the go pedal. I still miss that 'bark' of my old truck!! I thought that it was just my P pump truck that was different.



Bruce

 

[sparks57]

brkoyle:

You're cranking it for 30 seconds??? Something it wrong there buddy...

 

[Forrest Nearing]

agreed, you may need to tweak a couple things on that P pump... every one I've been around has fired up rather quickly. just not that instant bang that the VE pumps produce.

 

[cerberusiam]

brkoyle, jump into the 2nd gen forum and search on hard starting. There is a wealth of info on the problems with slow starting. The two that come to mind are leaks in the fuel lines between the lift pump and tank and I believe another issue is the rack travel not adjusted correctly. I think there was even a post about adjustment of the governor springs and starting.

 

[Gary - K7GLD]

In some ways, the mechanical function of the VE pump is similar to the VP - both operate the injector pistons via a cam-like ramp arrangement - the VE uses a rotating "wavy disc" that the pump pistions ride on sorta like a rollercoaster - where the VP pistons ride inside a "lumpy donut" with hills and valleys that cause the pistons to rise and fall. Both types allow injection timing change considerably easier than the P types. My old '91 would instantly fire up on the first piston to hit compression - my '02 is pretty quick too, but usually takes the second piston up - probably because it takes that long for the ECM to sense engine rotation and permit ignition...



Gotta LOVE computers...

 

[cerberusiam]

VP pistons ride inside a "lumpy donut"

Darn it Gary you mage me hungry, gonna have to make a run to Krispy Kremes... .



The 2nd cylinder up firing could be the computer or the 3 pistons the VP uses to generate the higher pressures taking another revolution to hit pop off pressure on the injectors or a combination of both. Aside from the lift pump issues the VP seems to be a fairly long lived piece. What have you seen or heard on life issues?



Since the higher pressures seem to be a power source I am wondering if it is possible to adapt the VP to a mechanical linkage rather than the computer module. All the computer is doing is changing the effective stroke for fuel delivery the same as the VE.



Anybody have a dead VP they want to donate for a high pressure mechanical VE/VP project?

 

[Gary - K7GLD]

I don't really think it's even remotely desireable to abandon the computer control of the VP-44 - that portion of it's operation seems quite reliable - and imagine an injector pump that can, on the fly, instantly change timing and adjust fuel delivery volume to suit changing engine demands and loads... No, you don't HAVE to imagine it, the VP-44 *does it*!



Later VP-44's seem to finally be significantly more reliable than early ones were - but reasonable precautions regarding cleanliness of fuel and regular use of fuel additives to enhance lubricity seem a good investment.



One fella has registered over a million miles on a VP-44 equipped truck, still with the original VP-44 - so they CAN last a long time!



I run added stages of fuel filtration on mine, and ALWAYS use a 50/50 mix of Power Service Diesel Kleen and Ashless synthetic 2-stroke oil to my fuel. If my pump fails, it dern sure won't be due to inattention or neglect!

 

[Forrest Nearing]

interesting... so it takes the P-7100 a sec to build enough pressure to pop the first injector, eh? whereas the VE is pretty much instant...



I've never been inside an injection pump, but I can totally picture how a lumpy donut would work in a rotary pump... anyone care to make an analogy that'd help me visualize how an inline pump works?



Forrest

 

[cerberusiam]

Forrest, not pressure to pop the injector, timing advance fire with a cold chamber. The P pump has a cam in the bottom that spins at the same rate as the cam gear. Injection occurs when the lobe reachs the designated lift in the sequence. Without the ability to advance that cam lobe cycle there is no mechanical advance. The VE is a rotary pump and uses a disk that has bumps on it for the injection cycle. To advance the injection timing the disk is turned opposite the rotation by supply pressure fed into a piston. If you crank up the fuel and advance the timing you get a pretty good rpm jump at starting until the fly weights pull things back down. Injecting the fuel earlier in the combustion cycle allows it to burn more and create more heat so things wind up easier. The noise your hearing is a pressure spike in the combustion chamber from the long burn time and extra fuel.



Clear as mud yet?

 

[Forrest Nearing]

actually clear as a creek... didn't realize it was a timing issue... I thought these things had static timing "curves"! (shows ya how much I know about these engines! LOL!)



Forrest

 

[cerberusiam]

Gary, so what do fueling boxes and injectors do to the life of the pump? Any hard data on performance mods and what to expect for pump life?



In a truck that is set up for the VP44 its not even a question. I am sure the benefits far outweigh the problems. The desirability to put the same efficiencies and capabilties that a 2002 has into a 1992, or any other vehicle, is what I am thinking of.



Question: Can I put the VP44 into my 92?



Answer: Not without a lot of head scratching and cussing!



Add to that the PCM is sourced from DC and the ECM is sourced from Bosch to Cummins specs and this could get frustrating. You better have some good friends in all 3 places that can get you the required specs for the interfaces otherwise it is a no run condition. Then there is that wonderful little piece called an APPS. Unless something has changed that was a DC specific item and they are really proud of it. What happens when they decide to NS1 that puppy? Granted, an aftermarket replacement should be available but it is just plain scary to think that needed electronic parts are just not available.



The same problems come into play when it comes to the auto transmissions. The 47RE/48RE will fit but there is no option other than custom for controlling the shifts.



It just smacks too much of planned obsolesence. Oh well, if all else fails I guess we have a reason to buy a new truck, ehh?

 

[Gary - K7GLD]

Only downside to performance boxes added to VP-44 injected engines is their tendency to quickly reveal the weak VP-44's!



Ones that are marginal will often immediately fail after adding a "box", or not too far down the road... Mine has been functioning perfectly for over 24,000 miles with an Edge Comp - so hopefully *I* got one of those "million mile" VP-44's