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Discussion Starter #1
I know this topic has had a few hits, but the search didnt get Me what I was looking for.
I just bought a 12 LML with 160k miles on it, it has been tuned with what I think to be H&S and the DPF system removed. when purchased it had replace fuel filter warning on and DTCs p0087 and p0088 for high and low fuel rail pressure. I replaced the fuel filter and cleared codes, but the p0087 low rail pressure has returned along with a drivability problem.
some times the truck runs strong with just a little haze on accel. but after running for a while and accelerating it will blow black smoke and fall flat.
one step at a time i have tested the fuel system and so far this is the results: when it looses power the fuel rail is commanding 26-28Kp but actual falls to 8 or less. at idle the vac. test is 5in. and at wot and full load its is in the 8-10 in range. removed the FPR from the pump for inspection and the screen was clean, no metal or debris.
I am leaning towards first replacing the pressure regulator and/or maybe the cp4. I have no plans of any major power increase, so I dont think doing a cp3 swap would be needed.
also seems that the cp4 may be original, and may be a good idea to go ahead and replace it before it self destructs.
 

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Usually if you're getting pressure codes, the pump is on the way out. A new regulator might help, but since you're out of warranty, I'd look at replacing it ASAP, preferably with a CP3, as they do have less issues with fuel supply than the CP4.

But a fresh CP4 and a lift pump should also do well.

Once a CP4 has the rail drained on it a few times, it's only a matter of time before she pops. If the FPR's are cheap enough, replacing them might not hurt, but I don't think it'll help.

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Discussion Starter #3
think I`m gonna order a new CP4, and replace it before the disaster. CP3 upgrade would be nice but there is a lot to doing that conversion. conversion kit, pump,egr delete, tune ect. money adds up quick. I have no plans of outrageous power, so a new pump,upgrade filtration,and lift pump.matbe get another 160,000 miles out of it.
if I had the option I would return the truck back all stock, exhaust ect.
 

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Discussion Starter #5
ran vacuum test on pump, was in spec, around 5 at idle and never above 10 at full throttle/full load and loosing power. a collapsed hose or bad pickup tube should have showed up.
 

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ran vacuum test on pump, was in spec, around 5 at idle and never above 10 at full throttle/full load and loosing power. a collapsed hose or bad pickup tube should have showed up.
I am assuming you checked vacuum at the test port ? With a new/clean filter you should be pulling 2"-3" and when it hits 5" I change my filters. So if your filter is good you might have a restriction somewhere.
 

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High Pressure Injection Pump (CP4.2 Pump)

Note: The CP4.2 pumps are not as durable as the CP3 pumps. Poor fuel supply, contamination, and/or running them out of fuel (plugged fuel filter) will cause them to fail. When they fail it is often catastrophic and they send metal particles throughout the high pressure side of the fuel system, causing further damage.

Check the fuel supply system first: see “Fuel Supply” above.

1) Before condemning the pump for a starting issue you need to be certain that the high pressure fuel system is not leaking the pressure. Check the injector return and the pressure control valve in the fuel rail.
2) If there has been a major contamination issue with dirt and or water then it is very likely that the high pressure pump will need to be replaced. The injectors are typically damaged as well if the pump is damaged.
2) If the pump will not build the desired pressure while cranking and everything else checks OK, remove the regulator from the pump and inspect for metal. If there is metal debris, the entire fuel system will need to be cleaned and/or replaced.

Fuel Supply and Fuel Filter Housing

The fuel filter housing (AKA fuel conditioning module in GM literature) is on the suction side (there is not a fuel supply pump from the factory on pick ups) and are prone to suck air. The 2011 and newer trucks are equipped with a “fuel filter pressure switch” that will open and trigger a “Fuel Filter Restricted” message in the IPC (instrument panel cluster) when supply restriction reaches 14”. Follow the GM fuel system diagnosis in the service manual.

1) Install fuel vacuum test tool.
2) Prime the fuel system with the hand primer until 10 PSI is indicated on the gauge, check for external leaks and repair. If the pressure drops from 10 PSI to 2 PSI in less than 1 minute, remove the fuel outlet line from the filter and cap it. Remove the ignition 1 relay and crank the engine for 2 – 15 second intervals, the high pressure pump should pull at least 12 inches of Hg vacuum. If air gets into the system it will cause a false/low reading.
3) Install clear hoses at the inlet and outlet of the fuel filter housing. Re-prime the system and then start the engine, there should be very little air going into or coming out of the fuel filter housing.
4) Common air ingestion places are the filter housing, drain valve, rubber hoses and quick connections. You need to use clear lines to isolate where the air is coming from and work your way back toward the tank until you don’t have any more air coming through the clear line. Unless you know where to get the tool that sees through black rubber lines to find air, your only other option is to bounce around and replace parts.

No Start or Hard Start

1) Check the injector returns:
2) Verify the fuel injector return line pressure is greater than 3 BAR (see “Fuel Injectors” for more information).
3) Unplug the fuel pressure regulator 2 (pressure control valve in left hand rail) electrical connector. Crank the engine for 15 seconds and verify there is a steady flow of fuel from the fitting on the rail. If there is not, proceed to checking/replacing the high pressure pump.
4) Remove the return hose from the fuel pressure regulator 2 (pressure control valve in left hand rail) and plug the hose. Crank the engine for 15 seconds and measure the fuel from the regulator. The volume of fuel should be less than 10 ml. If it is more, replace the regulator. The high pressure seal on the pressure control valve is one time use. Do not remove the pressure control valve unless you are sure it is defective and you are replacing it.
5) Check for air in fuel system; install clear lines before and after the filter housing to check for air in the lines.
6) Use a vacuum gauge to check the suction side of the fuel system. You should have no more than 5 inches Hg at WOT (wide open throttle) or 7-8 inches Hg under load. If you still have too much restriction after changing the filter, check for collapsing soft fuel lines by the drivers side valve cover and under the truck near the transmission. The fuel tank pick up may also be plugged. Too little vacuum (less than 2 inches Hg) means that it could be sucking air.
7) Confirm actual versus desired rail pressure even under crank no start conditions, to confirm the starting issue is rail pressure related. If rail pressure matches desired, diagnose other codes that may be related to starting problems.
1) (No Start) Disconnect the electrical connector and return line from one injector. Plug the fuel return line fitting with a suitable tool (CH-50377-A). Crank the engine for 15 seconds and verify no fuel leaks from the injector. If fuel leaks from the injector, replace it. Repeat for all eight injectors.
2) (Hard start but runs) Disconnect the return line from one injector. Plug the fuel return line fitting with a suitable tool (CH-50377-A). Use adapter CH-50378 (required to accurately test return, contains regulator to maintain injector return pressure) to route the injector return into a graduated container. Crank or idle the engine until fuel is dripping out of the line. Crank or idle the engine for 15 seconds and measure the return quantity. If the quantity is greater than 3 ml in 15 seconds, replace it. Repeat for all eight injectors.
8) Remove the high pressure regulator from the high pressure pump and check for metal debris. If there is metal found, the entire high pressure fuel system must be checked for metal and replaced as needed. GM recommends replacing the injection pump, rails, high pressure fuel lines, fuel injectors, fuel return rails, indirect fuel injector, and indirect injector fuel feed tubes if metal is found.(See picture under High Pressure Pump).

The maximum allowable leakage for one injector is 3 ml in 15 seconds, cranking or at idle.
The injectors require a minimum of 3 BAR (45 psi) of pressure in the return system. Pressure is maintained via a “Constant Pressure Regulator” at 4-11 BAR (58-160 PSI).

injector return is excessive at higher rail pressures which may cause the P0087 to set.
 

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Discussion Starter #8
never had any starting problems and during warm up engine performs well. but at operating temp and after making a couple of full power runs, the problem arises. ran vacuum test from start up and driving until problem showed up. vaccum reading at idle and under full load remain the same,but rail pressure drops. 160k miles on the original CP4, not gonna wait on the catastrophic failure. new pump comes with fuel pressure regulator so it may be a shot gun fix. doing the work Myself it is much less expensive to install a new CP4 than to do a retro fit CP3, and I dont plan on going to big power tunes ever.
 

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At least one good thing is your new OEM pump is $504.74 vs $949.99 for a new CP3.
Remanufactured CP3's are not much cheaper $844.33
 

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Lift pump
 

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Discussion Starter #11
Seems as some have had Injector problems along with pump failures, but for sure have had desasterous pump failures. As of now My pump has 160k on it and no metal particals and I know it is on barrowed time. So the pump is getting replaced along with EGR delete and a lift pump.
 

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New FPR you might be interested in.

Shop I am taking my truck to be deleted to has advised about a new fuel pressure regulator from Exergy that has a screen in it that should the Cp4 implode it will save injectors and rails.

I contacted Exergy and they confirmed their new product has two 20 micron screens as the oem fpr has one 80 micron screen.

At this time it is not anywhere on their site. So new it is only offered to their preferred performance shops.
 

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Discussion Starter #13
list of parts NOT causing My issues, CP4 pump. fuel pressure regulator on pump,fuel filter, restriction between pump and fuel pickup in tank. glad I`m not paying labor on this.
 

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Discussion Starter #14
well replaced left side fuel rail with pressure regulator and pressure sensor, and replaced unknown tuning with EFI live from Kurt at Farm Tuned Diesel. I now have a happy Duramax.
 

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Shop I am taking my truck to be deleted to has advised about a new fuel pressure regulator from Exergy that has a screen in it that should the Cp4 implode it will save injectors and rails.

I contacted Exergy and they confirmed their new product has two 20 micron screens as the oem fpr has one 80 micron screen.

At this time it is not anywhere on their site. So new it is only offered to their preferred performance shops.
I spoke with someone from exergy he told me they stock the regulator's now the price is $240 from what he said contaminated fuel is most likely the culprit in most cp4 failures another words if the fuel doesn't have the amount of lubricity the cp4 neeeds then your gonna have problem's with the cp4 and I'm thinking the tight tollerances of the cp4 vs cp3 may be the only reason the cp4 ever failed to begin with.
 

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I spoke with someone from exergy he told me they stock the regulator's now the price is $240 from what he said contaminated fuel is most likely the culprit in most cp4 failures another words if the fuel doesn't have the amount of lubricity the cp4 neeeds then your gonna have problem's with the cp4 and I'm thinking the tight tollerances of the cp4 vs cp3 may be the only reason the cp4 ever failed to begin with.
Shitty fuel and draining the rail kill the CP4. There's very few failures on trucks with lift pumps from new.

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I have had a fass 150 since 20000 miles I'm at 70000 now hopefully I"m ok. I did discover that my truck had a very restricted pick up tube for drawing the fuel out of the tank. The Fass 150 was cavitating until I put a sump in the tank now all is good. I almost feel like the cp4 pump is under to much stress having to suck the fuel thru the restricted sock in the tank.
 

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Check your fuel pressure regulator once and awhile, and you can likely catch it before catastrophic failure, if you're worried about it.

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I have had a fass 150 since 20000 miles I'm at 70000 now hopefully I"m ok. I did discover that my truck had a very restricted pick up tube for drawing the fuel out of the tank. The Fass 150 was cavitating until I put a sump in the tank now all is good. I almost feel like the cp4 pump is under to much stress having to suck the fuel thru the restricted sock in the tank.
Are you sure the in-tank sock is the diesel one? From other posts here, it seems if you buy a replacement for the in-tank mechanism, it, for whatever reason, comes with a gasoline sock [yes, even the diesel-specific parts], and you have to separately buy and install the diesel sock.
 

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I fitted a Bean's Sump kit too, to feed the hungry FASS 150.

Even just looking at the original plumbing between the bottom of the tank and the intake of the FASS gave me a headache. Thin drawstraw and tiny intake hole etc etc.

Far happier now ....and I've added a Kennedy pump before the FASS, with extra plumbing so I can bypass the FASS if it ever fails for any reason (eg: electric pump failure).

Bill Roach
Kadina, SA, Australia
 
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