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roegs
08-17-2003, 14:35
My '03 Helms Shop Manual shows an inline fuel pump used on the Duramax 6.6L cab/chassis trucks. Sorry, I'm a little green on this stuff. Is a lift pump the same as a fuel pump? Is there something different about the cab/chassis 6.6L engine that requires it to use a pump?
FirstDiesel
08-17-2003, 14:46
Where does it show the pump in the system??
I think the term lift pump comes from the fact that on the earlier model trucks the pump was used to "lift" the fuel from the tank to the injection pump.
SoCalDMAX
08-17-2003, 14:57
Scott,

The factory fuel pump is a dual pump, 1st stage is a lift pump to draw fuel. The 2nd stage is a high pressure (up to 25,000psi?) injection pump. They are built as an integral unit, so there is no external lift pump to see.

The factory pump is mounted all the way up front and high on the engine. It has to suck fuel from the tank through 17' of 7/16" line, a marginal sized filter that increases restriction when clogged, through an FICM which heats up the fuel and up 3' in elevation.

Throw in subzero to Death Valley operating temps and the vapor pressure and burn rate of the fuel may be all over the map.

To be honest, I've seen more robust filtration and fuel lines on VW powered dune buggies. IMHO, this system, installed on a powerful diesel engine, is marginal. It works, but I just don't think it's ideal.

But I also have 11 fans cooling different components in my computer, so my version of ideal is different than most. ;)

Regards, Steve
FirstDiesel
08-17-2003, 15:29
Steve

I'm wondering if your answer is correct for roegs question. He did say the book showed an inline pump for the chassis cabs. Could this be different from the regular models??
roegs
08-17-2003, 15:51
For those who might have the '03 manuals, the picture is on page 6-2897. Its a small unit about the size of a large filter (frozen orange juice can) that appears to mount on the frame rail in series with the line. From what I can see, the cab/chassis trucks use dual fuel tanks, and a pump mounted on the frame rail.
OC_DMAX
08-17-2003, 15:58
I believe the chassis/cab setup has two fuel tanks. The fuel pump you mention transfers fuel from the secondary tank to the primary tank. Saw the same thing in the 2002 Helms manual about a year ago and convinced myself the above explanation is correct.

SoCalDMAX's explanation of the injection pump is correct for our trucks (not too many of have the chassis/cab setup).
FirstDiesel
08-17-2003, 16:03
What section is that in your manual?? I'd like to look in the 2002 and see if it's there too.
jbplock
08-17-2003, 16:17
OC_DMAX is correct..
Back when we first started discussing lift pumps I also noticed that same picture in the Helms and posted a similar question. I can't remember whom, but someone jumped in and explained as OC_DMAX did that these pumps are only found on the Chassis Cab models and are used for fuel transfer. I think there is only one tank sender so fuel has to be transferred from the primary to the secondary as OC_DMAX pointed out.
smile.gif
SoCalDMAX
08-17-2003, 17:09
Oooops, sorry!

Good catch guys! I didn't see the chassis/cab part.

Regards, Steve
roegs
08-17-2003, 17:14
Thanks for the replies. Its unclear in the manual (Engine Controls 6.6L)as to what the pump is used for, but its probably as mentioned, as there looks to be a fuel sender on only one of the tanks.

Scott
imported_
08-17-2003, 17:55
Originally posted by SoCalDMAX:
Scott,

The factory fuel pump is a dual pump, 1st stage is a lift pump to draw fuel. The 2nd stage is a high pressure (up to 25,000psi?) injection pump. They are built as an integral unit, so there is no external lift pump to see.

The factory pump is mounted all the way up front and high on the engine. It has to suck fuel from the tank through 17' of 7/16" line, a marginal sized filter that increases restriction when clogged, through an FICM which heats up the fuel and up 3' in elevation.

Throw in subzero to Death Valley operating temps and the vapor pressure and burn rate of the fuel may be all over the map.

To be honest, I've seen more robust filtration and fuel lines on VW powered dune buggies. IMHO, this system, installed on a powerful diesel engine, is marginal. It works, but I just don't think it's ideal.

But I also have 11 fans cooling different components in my computer, so my version of ideal is different than most. ;)

Regards, Steve You use 11 fans to cool your computer...pfffttt!
Watercooling is where its at!... all 4 computers hooked up to a 2.5 gallon resevoir, 1 350 GPM magdrive pump and 4 800 silent fans mounted on top of a ford superduty heatercore.... much better system..... 30-60% overclocks on all processors (athlon and athlon XP) at full load their temps never exceed 50 celcius on an ambient of 25 celcius......
Modified
09-04-2003, 20:17
Per dmaxallitech, this dual tank option, with two senders, is a gas engine only option. Each fuel tank level sender sends a signal to the ECM, which is the only thing powering the Fuel Pump (FP) Relay, which powers the frame mounted lift pump. See more info @:

http://forum.thedieselpage.com/ubb/ultimatebb.php?ubb=get_topic;f=3;t=006694
dmaxalliTech
09-04-2003, 20:33
close, duel tanks are avail on the diesel, but I dont know if the transfer pump is powered from the same relay "port"...ahh, more research for me!