*Attention* No Lift pump installed on 2008-??? Freightliner w/Cummins ISB

[HaRVey 74.5]

Interesting post. If it is as you say that all modern Freightliner chassis do not come equipped with the required low pressure/high volume fuel delivery system that the 6.7 Cummins engine & CP3 pump requires, it sounds like a good case for a class action suit against Freightliner.
I'm going to contact Freightliner and Cummins regarding my VIN to see if there is a similar issue.
Thanks

[Jon_C]

I would contribute to this thread but i know from past experience its not a good thing to do. Good luck.

[IMDiesel]

Originally Posted by ShaunAED

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.

Just wondered if you supplemented the existing pump or removed it and are using just the new one?

[ShaunAED]

Originally Posted by IMDiesel

Just wondered if you supplemented the existing pump or removed it and are using just the new one?

That's the issue, no existing lift pump.

[ShaunAED]

Originally Posted by HaRVey 74.5

Interesting post. If it is as you say that all modern Freightliner chassis do not come equipped with the required low pressure/high volume fuel delivery system that the 6.7 Cummins engine & CP3 pump requires, it sounds like a good case for a class action suit against Freightliner.
I'm going to contact Freightliner and Cummins regarding my VIN to see if there is a similar issue.
Thanks

Keep us informed.
I'm assuming you'll here the same as I did.
Cummins: Lift pump in-tank required on 2007.5+ 6.7
Freightliner: No lift pump ever installed in tank of RV chassis, and it's a *cummins problem*.

[IMDiesel]

Originally Posted by ShaunAED

That's the issue, no existing lift pump.

Isn't the CP3 a pump?

[ShaunAED]

Originally Posted by IMDiesel

Isn't the CP3 a pump?

Yeah I went over this in another thread...but...

The CP3 has 3 high pressure chambers with pistons (high pressure outlet) fed by a low pressure (85psi) gear driven pump that sucks fuel from the tank. This gear driven pump does not need any pressure, but it does need volume of fuel to feed the high pressure side at proper rates. Failure to keep volume in line will result in excessive CP3 wear as the outlet of the Gear driven low pressure / vacuum pump also supplies fuel to lubricate the moving parts of the pump.

Per cummins the low pressure gear pump was not designed as a 'lift pump', but DOES have the capability of sucking fuel from the tank in the event of a lift pump failure, thereby not rendering the rig 'dead on the road'.

Like any vacuum pump there are major limitations, specifically the pressure differential created. It an only be 1BAR (in a perfect vacuum). 1Bar = 14.5psi.
Flow volume is determined by the fixed displacement of the pump.
Efficiency (pressure differential) is determined by the type of pump, RPM, etc. Typically around 85% for an internal gear pump. So .85 Bar or 12.3psi MAX pressure differential.

What this means is atmospheric pressure PUSHES the fuel in the tank up the pickup, thru the fuel line, thru the filters, and into the pump. That means the tank needs a vent to let in air, FYI.

The real problem is Dynamic Head, or pressure DROP across the system, which is determined by the length and volume of the feed line + any restrictions (like fuel filters). Since an RV fuel line is 80% larger in diameter and 2x+ longer than a truck, the pressure DROP across the system is FAR greater.
With any vacuum pump as length/volume of the feed line increases FLOW VOLUME decreases exponentially (not linearly). IE, double the length = 4x less flow, double the volume = 4x less flow.

It's not pressure the CP3 gear pump needs, it's proper volume.

As stated earlier the RV CP3 spins at 3x+ the rate of the truck CP3. This means volume is higher even though the pump is lower in flow.
If you wanted to do the calculations we almost have enough data...almost. It's the pressure drop vs flow we don't know.

As also stated the diesel needs fuel to make power, the CP3 needs volume to make pressure. IE the volume of fuel dictates the power that *can* be supported.
This means the Freightliner OE setup has a limit to the power it can support and it's variably dependent. (no clogged filters, properly vented tank, etc).

Take this information for what you will. In my personal rig the OE Freightliner setup could not support the 340/700 rating (with new filters, new sensors, new control valves, new CP3) but with the addition of the lift pump all shortcomings have been resolved.

[IMDiesel]

Ok,

So the CP3 is not designed as a full time lift pump. So I now see the need for the added lift pump.
Can you tell me if the 5.9 has a CP3 and a lift pump? and are they separate or the same pump?

I'm trying to understand how the 5.9L fuel pump works since Cummins changed it for the 6.7L.

And I'm wondering if the 5.9 would benefit from adding another lift pump to the tank as it is a long way from the engine.

[ShaunAED]

Originally Posted by IMDiesel

Ok,

So the CP3 is not designed as a full time lift pump. So I now see the need for the added lift pump.
Can you tell me if the 5.9 has a CP3 and a lift pump? and are they separate or the same pump?

I'm trying to understand how the 5.9L fuel pump works since Cummins changed it for the 6.7L.

And I'm wondering if the 5.9 would benefit from adding another lift pump to the tank as it is a long way from the engine.

5.9L pump is a different design.
In the truck world lift pumps are installed on the 5.9's to support modifications for more fuel.
Again, the trucks fuel system is shorter and has less volume than the RV, so flow is higher prior to lift pump installation.

[IMDiesel]

I'm talking the 5.9 in my RV .
it's still over 30' of distance to suck fuel.

[HaRVey 74.5]

Originally Posted by ShaunAED

Keep us informed.
I'm assuming you'll here the same as I did.
Cummins: Lift pump in-tank required on 2007.5+ 6.7
Freightliner: No lift pump ever installed in tank of RV chassis, and it's a *cummins problem*.

I sent email inquiries to both Freightliner and Cummins and confirmed that a lift pump is NOT included on their engines and per Cummins Service manual a lift pump is required from whoever/whatever it is going in to. From Freightliner I received confirmation that they DO NOT install lift pumps in their chassis or tanks.
I have requested resolution from Freightliner to their failing and solicited Thor''s assistance. We'll see if this goes anywhere or if there are other avenues to pursue corrective actions. This is clearly Freightliner''s responsibility, but how to hold them accountable is the question...

[HaRVey 74.5]

I also received an email from Freightliner that they "meet all the Cummins engineering specs and if not, why else would Cummins warranty their installations?" I forwarded that email to Cummins and asked how they reconciled Freightliner''s claim against Cummins statement that it is a requirement per the Cummins manual and asked fora clear explanation of the impacts of not having a lift pump (performance & reliability, etc.) and their recommendation for addressing the situation (i.e. instal a lift pump system of xxx gph & xx psi, etc.).
At least with documented responses and data from the 2 parties, I will have something to guide corrective action which will allow me to make the required fixes without voiding future claims.
It is incredibly frustrating to find Freightliner trying to avoid responsility for their error, but not surprising.
Anyone going to the Freightliner camp willing to address this with their representatives?

[HaRVey 74.5]

Update -
1) The Cummins service manual requires a "Lift Pump", which is actually only a manual push plunger primer on top of the fuel/water separator for priming the system after service and which Freightliner does supply, thus meeting the Cummins engineering spec.
2) however when asked Cummins for specific input fuel requirements for the CP3 pump, their rep responded with 30-94.3 psi... So I asked him to raise the inconsistency of the service manual verses what he stated to his leadership (is there a pressure requirement and hence the need for a in-line/in-tank pump or not, did the rep give me the right info or read the wrong data...)
3) I contacted Bosch directly regarding their CP3 pump (pn-5398557, number supplied by Cummins) to try to find out if there is an inlet pressure/volume requirement and got nowhere because all of that information is OEM specific (i.e. Cummins) and proprietary...
Argh!!!
At this point I'm just trying to get a scientific answer of what the correct fuel sup ply requiremnt is so I can do it myself if required or desired...

Darn you ShaunAED, see what you started! I'm sure you've been as frustrated as I with the combination of avoidance and ignorance and misdirection I've been experiencing! It's like NO ONE, not even Bosch can tell me the requirements of the pump that they designed and built!

[HaRVey 74.5]

Last one, I promise...
Mark Fraedrich at Freightliner found all of the Cummins information and drawings which showed that the CP3 pump has both a low and high pressure pump built in and it is in fact the output of the low pressure side which produces the 30-94.3 psi (as measured at the output of the fuel filter per diagnostic spec.).
So, while our 6.7 Cummins powered Freightliner chassis do not have in-tank or in-line "lift pumps", they do have combined low/high CP3 pumps designed to work independently of any other pump.
This does not mean that the addition of an in-line pump may not help, but not because of a manufacturer design issue.
It is amazing how many personnel and layers of tech "experts" at 3 different companies I had to go through to get this information, which in the end was answered by Mark at Freightliner without just passing it off! Thank you Mark!