Engine/Transmission (1998.5 - 2002) Why no cam-driven mechanical lift pump?

[MAX A/C]

OK, this is probably a dumb question, but I've not seen it mentioned anywhere, so I'm sure you guys will set me straight.



An article in Issue 35 states, "... the mechanical pump used from 1994-'98 provides about 17-22 psi fuel pressure at idle, and 25-30 psi at governed maximum engine speed".



So why can't the 24V engines still use a mechanical pump? If the pressures are too high, couldn't a pressure reducer be used? If it was a question of needing some pressure during cranking, I would think a "part time" electric pump could run for 2 seconds at cranking/firing, and then quit to allow the mechanical pump to take over. Seems like we'd have a much more reliable system that way. I think I read somewhere that there is no longer a lobe on the cam to drive it, but I'm wondering why it wouldn't work if the parts were in place..... So what's the easy answer?



Scott

 

[FourBarR]

my understanding is that cummins removed the lobe , when they went to the 24 valve. some early 98. 5 still have the hole in the block which is covered by a plate behind the lift pump. if you have a truck that has the hole in the block , you could change the cam and install the 12 valve lift pump. probably pricey to do.

 

[Ncostello]

I don't know what the real answer is... but I think a senior engineer at Cummins found some new engineer surfing the web. His punishment was to re-invent the wheel basically... or fuel pump rather. Unless Cummins was trying to squeeze every last drop of power and economy (perhaps emissions) out of this engine, I don't have another explanation. It worked fine. Perhaps the VP44 demanded more constant pressure. But a mechanical pump could have been designed around that constraint.



I like the mechanical pump on the 12V's. If the engine rotates... it WORKS. It don't get any simpler than that. The new lift pump wasn't a result of removing a lobe. Rather it was probably the new lift pump allowed the removal of the lobe. Less machine and material costs.



Whatever the answer they ruined a good thing as the reliability of these electric pumps is minimal at best. The heart of the engine is fed by a toy pump.

 

[rmrc]

I know it's a bit pricey,,,, but the new RASP system seems to be the answer regarding a mechanical solution for a reliable fuel system on the 24V engine!

 

[BTowler]

who sells the rasp?

 

[MAX A/C]

His punishment was to re-invent the wheel basically... or fuel pump rather.

That's what I was afraid of! There was no real reason to have taken it away! :{ Shoot, if I ever needed to replace my block, I think I'd go with one where I could put on the proven mechanical pump.



BTowler: www.koengineering.com I believe DTT transmissions sells them. If you haven't already, check out the long thread on the RASP a couple pages down.

 

[Double J]

Do it right the first time or join the club of frustrated electrical LP failures. Been there done that.