In Tank Lift Pump vs High Pressure Fuel Pump

DocB · **Posted:** Thu Nov 09, 2017 2:00 am

Lately, I've been having what I believe is fuel delivery issues. Hard start (cranks over longer before firing off) and irradic fuel rail pressures that coincide with irradic engine revs.
Additionally, it sounds like the in tank pump is intermitantly singing a little directly after start up.
150K on the clock.

So, do you believe this is a fuel pump issue and how do you diagnose if it is the in tank lift pump or the high pressure fuul pump?

TIA, help and advice greatly appreciated.

GordnadoCRD · **Posted:** Thu Nov 09, 2017 2:52 am

There isn't enough information here to indicate that either pump is at fault.

My first question is "How do you know you are having erratic fuel rail pressures"?

Do you have a way to check for sure that the rail pressure is erratic?
What precisely are they doing?
Do they drop below the requested pressure, then jump way up high, and continue cycling like that?
You must have some way to monitor live data to determine that.

If this is the case, and it's enough to make the idle speed jump around, then most likely neither pump is at fault.

flash7210 · **Posted:** Thu Nov 09, 2017 10:41 am

Yes, we need more data.
What rail pressures are you seeing?
What are the erratic rpm ranges?

If its a fuel rail pressure problem, a code will be set and it will go into limp mode (low power).

You need to check for codes.

mass-hole · **Posted:** Fri Nov 10, 2017 1:52 pm

Fuel rail pressure would appear erratic if you are changing the throttle or RPM at all. Unless you are in total steady state cruise it will bounce around like crazy.

GordnadoCRD · **Posted:** Fri Nov 10, 2017 8:13 pm

It will also do a rev - drop - rev - drop cycle if the FQS on the back of the HP CP3 unit is sticking. There are a number of things that will cause galling or sticking FQS valve, which will cause that behavior when the ported valve body sticks.

taroo · **Joined:** Sun Apr 27, 2008 2:14 pm **Posts:** 271

Your signature does not show a lift pump and
It does not come from the factory with one. Should we assume you have installed one? Your questions implies that you did but not sure.

DocB · **Posted:** Fri Nov 10, 2017 10:23 pm

I have NOT installed a lift pump.
Was under the impression that there was an OEM pump in the tank to feed the high pressure pump up front.
Is this not correct?

flash7210 · **Posted:** Fri Nov 10, 2017 10:39 pm

Your 2006 Liberty CRD did NOT come from the factory with a fuel pump in the fuel tank.

This is why many here recommend installing a lift pump to help supply fuel up to the engine and prevent air in fuel problems.

taroo · **Joined:** Sun Apr 27, 2008 2:14 pm **Posts:** 271

DocB wrote:

I have NOT installed a lift pump.
Was under the impression that there was an OEM pump in the tank to feed the high pressure pump up front.
Is this not correct?

No OEM liftpump. Glad I asked. Lots on the board on this topic. Adding one will ease starting and ensure 10-12 psi at the input to the belt driven high pressure pump. Not saying this will solve your problem but made mine consistently start more quickly and easier. Some of us also added a 2 micron secondary fuel filter. We are all trying to protect the life of the high pressure and expensive factory fuel pump while ensuring ease of starting.

DocB · **Posted:** Sun Nov 12, 2017 1:17 am

Thanks for all the help so far. Been watching the treads and have been pondering installing one.
Are these still the latest and greatest?:

Delphi FT4015
Spectra SP7236M
Spectra SP7181
Airtex E7181M
Dodge 3500 Cummins

OR is there a better one available today, meaning quality, correct continuous PSI, and sort of plug and play with harness?

OR one that you would suggest at this time?

Your help and suggestions greatly appreciated.

TURBO-DIESEL-FREAK · **Joined:** Sat Apr 17, 2010 3:29 pm **Posts:** 1167

Posting to follow along... I am also interested in what the best lift pump would be.

BocB, you should consider a Webasto heater if you are going to drop the tank for a lift pump, or at least consider the installation of the Webasto heater fuel tank stand pipe and hose for a heater installation later. :2cents:

GordnadoCRD · **Posted:** Sun Nov 12, 2017 3:35 am

DocB wrote:

Thanks for all the help so far. Been watching the treads and have been pondering installing one.
Are these still the latest and greatest?:

Delphi FT4015
Spectra SP7236M
Spectra SP7181
Airtex E7181M
Dodge 3500 Cummins

OR is there a better one available today, meaning quality, correct continuous PSI, and sort of plug and play with harness?

OR one that you would suggest at this time?

Better? Dunno, but it's working fine = Carter P76611M

Your help and suggestions greatly appreciated.

WWDiesel · **Posted:** Sun Nov 12, 2017 10:48 am

DocB wrote:

Thanks for all the help so far. Been watching the treads and have been pondering installing one.
Are these still the latest and greatest?:
Delphi FT4015
*Spectra SP7236M
*Spectra SP7181
Airtex E7181M
Dodge 3500 Cummins
OR is there a better one available today, meaning quality, correct continuous PSI, and sort of plug and play with harness?
OR one that you would suggest at this time?
Your help and suggestions greatly appreciated.

CARTER P76148M
I installed one of these in my Jeep CRD back in 2013!
Can be easily found on eBay, Amazon, and many other vendors!
It is probably the most popular pump used for retrofit and the same one Sasquatch sells!

*Note: FYI, Spectra does not have a good reputation according to my local Autozone Commercial Manager. :roll:

https://shop.sasquatchparts.com/product ... 5143160aa/

GordnadoCRD · **Posted:** Sun Nov 12, 2017 2:17 pm

With so many choices, I wonder if there is any commonality between the ones lately reported to have come apart in the tank?

WWDiesel · **Posted:** Sun Nov 12, 2017 3:48 pm

GordnadoCRD wrote:

With so many choices, I wonder if there is any commonality between the ones lately reported to have come apart in the tank?

Good question, I would be very curious of the brands that failed! :roll:

dennyb · **Joined:** Wed Aug 13, 2014 4:27 pm **Posts:** 110

Some have had factory pickup come apart. Not an aftermarket pump and pickup. Plastic failure and rods bounce around in tank.

Perfect time to upgrade to lift pump.

WWDiesel · **Posted:** Sun Nov 12, 2017 4:31 pm

dennyb wrote:

Some have had factory pickup come apart. Not an aftermarket pump and pickup. Plastic failure and rods bounce around in tank.

Perfect time to upgrade to lift pump.

Thanks, that good info!
Best of my knowledge, I have not read of any failures so far of a retrofit lift pump in a Jeep CRD.

DocB · **Posted:** Sun Nov 12, 2017 10:47 pm

At this time, for this vehicle, is there any consensus as to what the best PSI output of the lift pump should be as to provide enough pressure, but not to much to facilitate aeration?

Asking this because I see that two different pumps from the same manufacturer have been suggested.

GordnadoCRD · **Posted:** Mon Nov 13, 2017 1:15 am

Aeration cannot happen with in-tank air pump.

Edit: to be more precise - IF aeration happens with an in-tank lift pump... you're out of fuel.

Output pressure has no connection to suction-side aeration of external lift pump, as it's identical as the CP3 pump.

WWDiesel · **Posted:** Mon Nov 13, 2017 1:23 pm

DocB wrote:

At this time, for this vehicle, is there any consensus as to what the best PSI output of the lift pump should be as to provide enough pressure, but not to much to facilitate aeration?

Asking this because I see that two different pumps from the same manufacturer have been suggested.

Any low pressure pump in the range of 10-15 psig will suffice just fine!
One consideration; make sure that any pump you get will allow fuel to flow through it if it were to lose power or fail for some reason.
That way your CP3 could still pull fuel from the tank and not leave you stranded on the side of the road! :wink:

Most recommend and use the Carter P76148M

In Tank Lift Pump vs High Pressure Fuel Pump

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