isb and hpcr, the differences?

[PLohr]

I have been searching this forum and haven't found my answer as of yet. I noticed in the TDR publication I received this month (the current issue), 2003 and newer Dodge Rams use HPCR while 2002 and earlier use ISB. What are the differences between the two systems? Is one system quieter than the other? Thanks for any help.

 

[DPelletier]

The pre '03 24V uses a Bosch VP-44 injection pump to time and pressurize the fuel. The injectors on this system are nothing more than nozzles



The HPCR uses a CP-3 pump to pressurize the common rail (which is a plenum, basically) and then the injectors (which are equipped with solenoids) are computer controlled to time the injections.



The advantages of the common rail are that the engineers can program the system for a wide range of conditions and it lends itself to more "micro management" of the fuel system. The HPCR equipped engines are quieter than the VP-44 engines in a large part due to the pilot injection system which allows a small amount of fuel into the combustion chamber prior to the main shot to allow the flame front to detonate less violently. In the field, the HPCR CP-3 pumps seem to be far less prone to catastrophic failure (usually induced by a failed lift pump) than the VP-44.



The advantages of the VP-44 (IMO) are that in the event you have an injector solenoid failure in the open position, the HPCR engine can, and will, torch a cylinder. Doesn't happen often, but it is more of a risk on the HPCR than the VP-44 equipped trucks.



Cheers,

Dave

 

[Alan Reagan]

Nice explanation, Dave.

 

[DPelletier]

Thanks.



One clarification though; ISB or ISBe refers to the engine itself, not the injection system. I meant to say that in my earlier reply.



Dave

 

[PLohr]

Thank you for the detailed explanation. Its an interesting point about the possibility of an HPCR injector hanging open and the damage that will occur.

 

[DPelletier]

No problem,



HPCR also has a couple of other minor advantages that I didn't mention; it apparently has enhanced cold starting ability and you don't have to bleed the injection lines if you run out of fuel.

But while I'm doing comparisons, I'd be remiss if I didn't also say that 24V ETH (HO) engines equipped with an HX35 turbo would appear to have more power potential (without replacing turbos) than the HPCR engines with HY35 turbos. Or at least more useable power (lower EGT's).



Dave

 

[Roger rodbolt]

These differences aren't in the fuel injection but don't forget the "swirl cooled pistons", layered head gasket and solid side cover block on the ISBe. lc