Another Reason for a Lift Pump on a Duramax? - Chevy and GMC Duramax Diesel Forum
Performance Upgrades Discuss what Intakes,Exhaust,Fuel System,Programmers,Tuners,&Trans. are right for you.

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post #1 of 20 (permalink) Old 10-14-2019, 08:36 AM Thread Starter
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Another Reason for a Lift Pump on a Duramax?

Hi folks-

Making no assumptions here, as working on diesels is not my day job:

I'm at 100,000 miles on my factory original stock 2015.5 GMC Denali HD.

After installing a lift pump which puts out 95 GPH at 11 PSI (indicated by analog gauge mounted on the pump output to engine ), I had a leak the morning after install when I used remote start. in that ten minutes, the truck dripped a basketball- sized puddle under it.

I found the leak and tracked it back to the primer/ plunger at the fuel filter head.

The leak had all but stopped on its own when the new oring seal kit for the filter head arrived.

When I removed and disassembled the fuel filter head, I found a decent amount of dried, crusty DEF crystals all over and inside the plunger assembly- under the triangular plate and on and around the orings in the plunger. Flakes between the metal plunger and the plastic with two o-rings found as well.

Apparently, the liquid DEF burping back out of the tank and sloshing everywhere was seeping into the filter head and drying to form small flakes. These allowed the fuel to leak past and then basically stopped leaking.

I cleaned the crap out of everywhere, replaced and lubricated the o- rings. And now, no leaks.

So- here is what I want to float out there:
If it was leaking at that pressure with DEF flakes in it- Does that mean that it was sucking air before that?

How many of us who have these trucks are driving around with $CP4 drawing air into the fuel at the filter head and don't know it?

I did not dyno or drag race the truck to prove it, but i felt a performance improvement after installing the lift pump. Is this why?

If it is, then I would suggest a lift pump be installed on all Duramaxes - stock or otherwise. This alone might reduce the number of $CP4 failures.

I've also put a plastic bag around the filter head to keep it clean from now on.

Just my random thoughts.

2015.5 GMC Denali HD LML 6.6' bed CC SRW
EMISSIONS ON, Resonator delete, PCV relocation, AFE Rear Diff Cover, 34.5" Toyo AT2 Tires, Bilstein Shocks, FASS 95gph/ lowered PSI lift pump, Exergy Fuel System Saver, Dirty Hooker Diesel Line Pressure Modifier, Edge Insight CTS2 Monitor
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post #2 of 20 (permalink) Old 10-14-2019, 08:58 AM
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If you think cramming 11psi of fuel pressure down the throat of a CP4 is going to help it live longer, you are sadly mistaken....
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post #3 of 20 (permalink) Old 10-14-2019, 09:32 AM Thread Starter
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So are you saying that delivering fuel to the pump under moderate pressure will have an adverse effect on longevity? If so, please elaborate. This was not my concern. My focus was on the possibility of the CP4 under normal conditions pulling somewhere between 5 and 10" of vacuum and drawing air past the parts where it leaked after the lift pump install.

2015.5 GMC Denali HD LML 6.6' bed CC SRW
EMISSIONS ON, Resonator delete, PCV relocation, AFE Rear Diff Cover, 34.5" Toyo AT2 Tires, Bilstein Shocks, FASS 95gph/ lowered PSI lift pump, Exergy Fuel System Saver, Dirty Hooker Diesel Line Pressure Modifier, Edge Insight CTS2 Monitor
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post #4 of 20 (permalink) Old 10-14-2019, 10:50 AM
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A suggestion

go do a little research using this forum's "search" on the CP4 / CP3 issues.

You will find many examples of people who have had good luck with their CP4's - giving hundreds of thousands of miles of trouble-free service. Many of these claim that is because they used various kinds of fuel lubricants, additional fuel pumps, and/or whispered sweet love messages to them.

You will find many examples of people who have had bad luck with their CP4's - in most cases their first awareness that their CP4 has failed, is when they are stuck on the side of the road awading a "roll-on". Their second awareness is when they find that CP4 failure generally trashes the entire fuel system, meaning about a eight grand or more repair. A question I cannot answer is whether using various kinds of fuel lubricants, additional fuel pumps, and/or whispered sweet love messages to them is "the answer" to avoiding CP4 failure.

You will find many examples ( such as me) who have removed or had removed the CP4, replacing it with the CP 3. ( as a side-note, for those who live in a "inspection area" and or are still under warranty & thus cannot do a "delete", some sellers of CP3 kits have a "CARB approved" version.

If you can find ONE example of someone who has been left on the side of the road with a failed CP3 failure, at the very least, someone should award you with a nice, fresh chocolate chip cookie.....

You may draw such conclusions from my post as you deem wise & appropriate.....!

2013 3500 long bed crew cab. Purchased at approx. 80,000; now have 91,000, convert to CP3. DPF "triggerd" a limp mode, so was cut out of the vehicle & cleaned by a DPF cleaning co., on re-installation, everything back to normal. Would never ever think of something as nasty and as anti bunny wabbet as a full-delete...after all..dosnt everyone like the fun & excitement of being stuck by the side of a Interstate in the ran while towing when one's truck's computer decides to go into "limp mode"...?.
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post #5 of 20 (permalink) Old 10-14-2019, 11:04 AM
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Quote:
Originally Posted by LMLLover View Post
If you think cramming 11psi of fuel pressure down the throat of a CP4 is going to help it live longer, you are sadly mistaken....
So how much pressure head should a lift pump deliver at the CP4 inlet, and how did you determine this value?

2017 Silverado 3500 LTZ (Summit White) | CC SB SRW | Z71 | Duramax L5P | Undercover Ultra Flex bed cover | Draw-Tite front receiver | AIMS 3kw inverter-charger | Titan Travel Trekker 50-gallon auxiliary fuel tank
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post #6 of 20 (permalink) Old 10-14-2019, 11:04 AM
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I'm a firm believer that a lift pump should be one of the first modifications to any of these trucks no matter the year with the exception of the new trucks that I believe come with one. Now remember that this is just my opinion.
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2001 2500HD 4WD EXTENDED CAB LS,
S&B CAI, 4" STAINLESS STEEL EXHAUST, EFI LIVE FROM ATP TRUCKS, EDGE CTS, PPE BOOST VALVE, BANKS INTERCOOLER PIPE, AIR DOG II 165, REBUILT TRANNY WITH SUNCOAST KIT, TRANSGO SHIFTKIT AND BILLIT TORQUE CONVERTER, NEW UPGRADED TAILSHAFT, PUMP RUB FIX ON TRANSFER WITH NEW ALUMINUM TAIL SHAFT, NEW TOW MIRRORS, NEW GAGE HEAVY DUTY FRONT AND REAR BUMPERS, BEANS SUMP, FUMOTO VALVE, RARE PARTS TIE RODS WITH COGNITO PISK, MAD JACK FUEL FILTER ACCESS DOOR, STAINLESS STEEL SPEED BLEEDERS.
2011 GMC 3500HD DUALLY Welding Bed, 4WD CREW CAB, 4" downpipe back exhaust, def delete, egr delete, with new LB7 up pipe, pcv reroute, Fass 150, EFI live with DSP 5, HSP CAI. Air Lift Air bags. PPEI transmission tune.
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post #7 of 20 (permalink) Old 10-14-2019, 11:55 AM Thread Starter
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Quote:
Originally Posted by 6686L View Post
A suggestion

go do a little research using this forum's "search" on the CP4 / CP3 issues.

You will find many examples of people who have had good luck with their CP4's - giving hundreds of thousands of miles of trouble-free service. Many of these claim that is because they used various kinds of fuel lubricants, additional fuel pumps, and/or whispered sweet love messages to them.

You will find many examples of people who have had bad luck with their CP4's - in most cases their first awareness that their CP4 has failed, is when they are stuck on the side of the road awading a "roll-on". Their second awareness is when they find that CP4 failure generally trashes the entire fuel system, meaning about a eight grand or more repair. A question I cannot answer is whether using various kinds of fuel lubricants, additional fuel pumps, and/or whispered sweet love messages to them is "the answer" to avoiding CP4 failure.

You will find many examples ( such as me) who have removed or had removed the CP4, replacing it with the CP 3. ( as a side-note, for those who live in a "inspection area" and or are still under warranty & thus cannot do a "delete", some sellers of CP3 kits have a "CARB approved" version.

If you can find ONE example of someone who has been left on the side of the road with a failed CP3 failure, at the very least, someone should award you with a nice, fresh chocolate chip cookie.....

You may draw such conclusions from my post as you deem wise & appropriate.....!
I do like cookies.

2015.5 GMC Denali HD LML 6.6' bed CC SRW
EMISSIONS ON, Resonator delete, PCV relocation, AFE Rear Diff Cover, 34.5" Toyo AT2 Tires, Bilstein Shocks, FASS 95gph/ lowered PSI lift pump, Exergy Fuel System Saver, Dirty Hooker Diesel Line Pressure Modifier, Edge Insight CTS2 Monitor
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post #8 of 20 (permalink) Old 10-14-2019, 12:50 PM
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The "feed" section of a CP3 / CP4 pump is designed to draw fuel from the tank, and deliver it to the high pressure section.

My LLY has been doing that successfuly for 300k+ miles now... without issue.

I also run a Racor filter keep my filter head and fuel lines in good condition.

Whenever you see a post where a guy adds a lift pump, and suddenly his rig runs 10x better, the lift pump is overcoming some other issue, like collapsed fuel lines. This is the main benefit of a lift pump.

Someone once posted a photo where the pumping gears in a CP3 feed pump wore into the housing from excessive lift pump inlet pressure. All the debris went straight through into the high pressure side, and on to the injectors.

Not good.....

John Kennedy has made 900hp or so, off of 6 psi of fuel pressure on one of his double-pump setups.

I run a Kennedy single pump on my LML at 4psi, measured at the CP4 fuel inlet.

I run a lift pump on my LML, for the added filtration and water separation. I dont run one to max out the delivery pressure, and wipe out my feed pump gears in the process.

The feed pump gears operate like a revolving door at a department store. It will only allow so many shoppers through at a time, no matter how many are crammed into a line to get in.

Excess fuel pressure is a poor idea, but high GPH numbers and PSI is what sells pumps to the uninformed.

95 GPH is over 1000hp ..... how many GPH do you think you need to go down the highway? 20 mpg = 3GPH @ 60 mph.
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post #9 of 20 (permalink) Old 10-14-2019, 12:57 PM
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Quote:
Originally Posted by LMLLover View Post
If you think cramming 11psi of fuel pressure down the throat of a CP4 is going to help it live longer, you are sadly mistaken....
I ran 10 to 12 psi on my fass when it was stock cp4 for 145k miles. Never had an issue. Cp4 was in great health when pulled. Lb7 lly the higher lp pressure would effect the ficm or the fpr and cause idling issues. The lbz to lmm usually do fine with anywhere from 7 to 12 psi. On a stock fuel truck 6 to 7 is fine. Really any positive pressure is enough. If its dropping rail pressure at wot crank it up, if its making rail pressure fluctuate at idle drop it down.
My race truck with dual pumps( 10mm stroker and cp3k) with 150% over injectors drops my ad150 from 14 psi to 2 at wot on a 1200us tune. Bigger tunes it pulls it below and rail starts to dip slightly. Turned the pump up to 25psi and it stays around 6psi wot most of the time.
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Last edited by SilverGorillaLML; 10-14-2019 at 01:04 PM.
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post #10 of 20 (permalink) Old 10-14-2019, 03:33 PM
J83
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Quote:
Originally Posted by LMLMAO View Post
Hi folks-

Making no assumptions here, as working on diesels is not my day job:

I'm at 100,000 miles on my factory original stock 2015.5 GMC Denali HD.

After installing a lift pump which puts out 95 GPH at 11 PSI (indicated by analog gauge mounted on the pump output to engine ), I had a leak the morning after install when I used remote start. in that ten minutes, the truck dripped a basketball- sized puddle under it.

I found the leak and tracked it back to the primer/ plunger at the fuel filter head.

The leak had all but stopped on its own when the new oring seal kit for the filter head arrived.

When I removed and disassembled the fuel filter head, I found a decent amount of dried, crusty DEF crystals all over and inside the plunger assembly- under the triangular plate and on and around the orings in the plunger. Flakes between the metal plunger and the plastic with two o-rings found as well.

Apparently, the liquid DEF burping back out of the tank and sloshing everywhere was seeping into the filter head and drying to form small flakes. These allowed the fuel to leak past and then basically stopped leaking.

I cleaned the crap out of everywhere, replaced and lubricated the o- rings. And now, no leaks.

So- here is what I want to float out there:
If it was leaking at that pressure with DEF flakes in it- Does that mean that it was sucking air before that?

Its likely there was some getting in, air is much less dense so it would be easier to pull air through the leak than to pull fuel up from the tank. Did the truck ever randomly stall on you before, or ever fail to start without a LOT of cranking? i had the exact same problem on my 15.5, though i just replaced the whole head for 40 bucks more with a filter on it instead of doing the rebuild so i dont know if it was DEF related or not.

How many of us who have these trucks are driving around with $CP4 drawing air into the fuel at the filter head and don't know it?

I did not dyno or drag race the truck to prove it, but i felt a performance improvement after installing the lift pump. Is this why?

probably, i felt, and heard in the sound of the engine running a significant difference after i fixed the leak in my filter head.

If it is, then I would suggest a lift pump be installed on all Duramaxes - stock or otherwise. This alone might reduce the number of $CP4 failures.

to be fair, the new trucks do have lift pumps from the factory. while i agree they should all have lift pumps stock, the real issue here is the lousy location of the filter head.

I've also put a plastic bag around the filter head to keep it clean from now on.

Just my random thoughts.

i bought this. THIS should have come from the factory.....

GMC & CHEVY Duramax Fuel Filter Relocation Kit - Western Diesel



Quote:
Originally Posted by LMLMAO View Post
So are you saying that delivering fuel to the pump under moderate pressure will have an adverse effect on longevity? If so, please elaborate. This was not my concern. My focus was on the possibility of the CP4 under normal conditions pulling somewhere between 5 and 10" of vacuum and drawing air past the parts where it leaked after the lift pump install.

the pressure at the inlet of the pump should be almost nothing, high pressure loads the input of the pump and increase the wear due to higher loads on the gear faces. the lift pump should be dialed back so the pressure at the CP4 inlet is only a pound or two. You want to push the fuel to the pump, not pressurize the inlet of the pump. Think of it more like relocating the CP4 inside the tank rather than adding a fuel pump.


Quote:
Originally Posted by jdwarren View Post
So how much pressure head should a lift pump deliver at the CP4 inlet, and how did you determine this value?
I have to say, i agree with him, maybe not to the doom and gloom extent it was put, but i would not be running anything over 5 PSI at the CP4 inlet. There is just no need, the pump puts out so much more fuel than the CP4 would ever pull in that your never going to drain the fuel line even at 0-1 PSI. Running higher is just going to increase loads inside the pump.

The lift pump just needs to provide flow, and remove the vacuum load on the pump, nothing more. Will running it at 11 blow your truck up? probably not. But unless your making SilverGorilla levels of power, i also dont think its helping any. So if there is no gain, and a risk of failure, seems like an easy solution would be to dial the pressure down a bit.

If you have a twin / triplet monster that you sled pull or race with, you may be the exception to the rule.

2015 Chevy Silverado 2500 HD 6.6L LML

Last edited by J83; 10-14-2019 at 03:48 PM.
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