Community Forums

ShaunAED · 11-11-2019, 10:33 AM

Experiencing fuel starvation?
High Pressure Fuel pump (CP3) taking a dump?

Well....there's a reason.

5.9L ISB Cummins has a lift pump mounted ON the engine, therefore no lift pump supplied by Freightliner was necessary.

Starting with the EPA07 6.7L ISB the Lift Pumps were moved to the Fuel Tank (in the light duty trucks).
The midrange CP3 used for the RV 6.7 ISB also needs a Lift Pump (according to Cummins), but Freightliner DID NOT install one in the fuel tank, or in line.

Hence low fuel pressure and low power, followed by CP3 failure.

CP3 has a failsafe feature that allows it to pull fuel from the tank in the event of Lift Pump failure. This feature was not intended to be used as the primary lift pump. GM HAS used it like this, but Cummins does not. IMO if you can help feed the CP3 with gravity it'll last a lot longer, but a lift pump is what SHOULD be used.

I post this as we just purchased our First Motorhome. A 2008 Itasca with 6.7L ISB and 23K miles on the clock. After noticing a severe lack of power and following up on all maintenance (fuel filters, trans filter, trans fluid swap, diff fluid swap, oil / filter change, coolant, DPF cleaning, etc) the coach still had a lack of power. To the point the engine surges at 1/2+ throttle, makes 17-19psi boost MAX, and struggles up minor grades at 45MPH.

I replaced the Cascade overflow valve, fuel pressure sensor, fuel pressure regulator valve, and fuel pressure relief valve. Upon removing the fuel pressure sensor ON the rail after driving 15min and letting the coach sit for 15-20min, there was only a trickle of fuel that came out of the fuel rail. (Obviously a lack of fuel volume to the rail).

Following an exhaustive search for the lift pump I contacted Freightliner and with the VIN they confirmed there was NO lift pump installed in the tank or line of this coach. I then contacted Cummins and confirmed there was NO lift pump installed on the 6.7ISB unlike the 5.9. Cummins confirmed a lift pump in the tank was to be used with the 6.7 ISB, and that was up to the manufacture of the chassis to install.
Called Freightliner back and they laid blame on Cummins.

So.... a New Midrange (RV style) CP3 is $2000, and a retrofit lift pump $500 or so pretty easy once you figure in wiring and fittings.
Not to mention labor.

Just an FYI for anyone with the Freightliner Chassis and 6.7ISB. If you experience a Lack Of Power that is Fuel related.....you now know why.

Ray,IN · 11-11-2019, 08:14 PM

I would investigate having your injector pump rebuilt. Almost any diesel shop can rebuild pumps.
As to the lift pump, instead I would investigate installing a FASS fuel pump/filter system. There are threads here from members who have installed a FASS system on their MH and all sing praises. I would be redundant to attempt to explain what you may read.

ShaunAED · 11-12-2019, 08:29 AM

'Rebuilding' a High Pressure fuel pump where the piston to wall clearance is .0005" at a 'shop'. LMAO
I own a performance shop, we build race cars, and engines. There is NO WAY a local diesel shop will do more than simply replacing gaskets and seals +cleaning. If the CP3 pistons/walls have been damaged from a lack of lubricating fuel (Cascade overflow valve has 2 lubricating circuits that are open at different pressures), I'd simply be wasting $$$ and getting back a unit that wouldn't be able to push the volume/pressure as a new or OEM remaned unit would.

FASS is junk.
Been down that road before.

I've got an AFE 42-3001 on the way along with the parker fittings to connect to the Freightliner 5/8 fuel line.

I'm debating on using the fuel tank drain port as the inlet using Stainless Steel hardline and fittings and having the pump mounted low for gravity feed, or putting it in the frame rail. Obviously the closer the pump is to the source, and the lower it is, the better it'll work.

I also need to figure out where to have the pump triggered. Key ON is fine, but I want the pump to shut off after a few seconds of Prime like a factory setup and not run 100% of the time with the key ON, like when leveling the rig.

Ray,IN · 11-13-2019, 08:15 AM

You are right of couse Shaun, that's why I said rebuild in instead of re-manufacture. I retired from tool N die making so I know all about tolerances. I have worked with tolerances as small as a micro-inch.
I agree again, a pump will push better than it can pull.

deprived · 11-26-2019, 06:14 AM

Quote:

Originally Posted by ShaunAED

Starting with the EPA07 ... Freightliner DID NOT install one in the fuel tank, or in line.

anyone with the Freightliner Chassis and 6.7ISB.

I just want to be sure I understand you: You are saying that the in-tank lift pump found on most Cummins/Freightliner setups has been omitted from certain Freightliner/6.7L setups in favor of an engine-mounted lift pump.

This is interesting. I have a 2008 Tiffin on a Freightliner chassis with a Cummins 6.7, however my rig is one of the short-lived front-engined setups. I wonder if this applies to me as well. I have a 2008 Freightliner shop manual but it only sort-of covers my rig.

Where on the engine is the external pump mounted? I'd like to see if my RV has set up this way.

ShaunAED · 11-26-2019, 04:14 PM

Quote:

Originally Posted by deprived

I just want to be sure I understand you: You are saying that the in-tank lift pump found on most Cummins/Freightliner setups has been omitted from certain Freightliner/6.7L setups in favor of an engine-mounted lift pump.

This is interesting. I have a 2008 Tiffin on a Freightliner chassis with a Cummins 6.7, however my rig is one of the short-lived front-engined setups. I wonder if this applies to me as well. I have a 2008 Freightliner shop manual but it only sort-of covers my rig.

Where on the engine is the external pump mounted? I'd like to see if my RV has set up this way.

According to Freightliner, they have NEVER installed an in-tank lift pump on ANY cummins equipped chassis.

I can confirm this is the case with our 6.7L 2008 Model Year Freightliner chassis.

The midrange CP3 (high pressure fuel pump) is located on the engine at the rear (not the front cover like truck applications). It is turned by a gear in the REAR cover. (transmission bell housing)

ShaunAED · 12-12-2019, 06:46 PM

New CP3 installed, still NO POWER.
Old CP3 disassembled and found to be 'just fine'.

Next step is to drop the tank and inspect for blockage / air leaks, and install the AFE Lift pump that just showed up today. (VERY nice piece BTW).

deprived · 12-13-2019, 05:55 PM

Quote:

Originally Posted by ShaunAED

I can confirm this is the case with our 6.7L 2008 Model Year Freightliner chassis.

What rig do you have?

ShaunAED · 12-13-2019, 06:37 PM

Quote:

Originally Posted by deprived

What rig do you have?

Itasca Latitude 39W

ShaunAED · 12-16-2019, 04:39 PM

Lift pump installed, set on the lowest pressure (10psi).

Rig sees more boost now, and it comes in faster, takes less throttle to stay at speed, and holds MPH better on the grades as well.

Don't get me wrong, it's still a turd (340HP 6.7), but it's at least up to spec now.

deprived · 12-17-2019, 02:28 AM

Quote:

Originally Posted by ShaunAED

Lift pump installed, set on the lowest pressure (10psi)
Don't get me wrong, it's still a turd \

My 6.7 is tuned to 300HP (an even bigger turd), so I am very interested in your situation. Which model pump did you end up using and, if you don't mind saying, how much did it cost?

Thanks for the info, BTW.

ShaunAED · 12-17-2019, 08:31 AM

Quote:

Originally Posted by deprived

My 6.7 is tuned to 300HP (an even bigger turd), so I am very interested in your situation. Which model pump did you end up using and, if you don't mind saying, how much did it cost?

Thanks for the info, BTW.

AFE DFS780
https://afepower.com/afe-power-42-30...80-stand-alone

You will also need the correct Parker fittings for the 5/8" fuel line:
https://www.amazon.com/Parker-Brake-.../dp/B077PBF6QK

The AFE supplied power wire was long enough to reach the front Fuse/relay box (engine fuse/relays in this box on my rig) and from there into the cab under the dash.
If you just want an ignition ON setup, the ignition (key) behind the dash has extra tabs to connect a Spade connector for a very easy install. I installed a switch to turn the pump OFF. (Like key ON leveling)

The only hickup is I had to install the pump upside down due to the in/out positions and mounting where the fuel line runs in the Passenger side frame rail.

deprived · 12-17-2019, 02:53 PM

Quote:

Originally Posted by ShaunAED

I installed a switch to turn the pump OFF. (Like key ON leveling)

Good thinking.

Thanks for the info!

ShaunAED · 12-17-2019, 03:18 PM

FYI, diesel power is ALL about fuel, but the ECU controls boost as well.
More fuel = more boost up until the point the ECU pulls down boost for control.

My Rig saw a max of 23-24psi boost before the pump install. It now sees 27 and then drops to 24-26psi as the ECU pulls power via Boost control. It does get to peak boost faster, but 2-4psi gain is nominal in power increase. (probably 20-30HP max)
Since it gets into boost faster it does gain more TQ, but still not enough for the rig IMO.

Next step is to install a programmer to allow more boost peak and add more fuel across the RPM band.

The end result will be LOTS more TQ as fueling down low is increased (along with more boost faster) and maximum boost increased for higher HP (along with more fuel). Now that the fuel system can keep up, this should get us where we need (55MPH up our 3 and 4% grades) while towing the Race car (5000lbs).

Oh, another tid bit of valuable info. The CP3 on the 6.7 Truck flows MORE than the RV but turns at a 1:1 ratio vs engine speed. The Midrange RV 6.7 CP3 flows less but is turned by a very large gear in the rear of the engine (I can only guess at the ratio but likely between 3 and 5:1).
This means the RV 6.7 CP3 has more total flow vs engine RPM, so there is no need to 'upgrade' to a modified unit. We just need to feed it low pressure volume.
I believe 200lph for the truck and 175lph for the RV.
This is measured at a specific RPM of the pump.