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Discussion Starter #1 (Edited)
Long story, so I'm going for it. I work at a GM dealer (parts counter). My friend traded in his beloved 2006 LBZ Crew Cab 4x4 HD. 229k on it. Why did he trade it in? Here it goes:

Back in September/October 2016, he was towing his dump trailer no load in it. CP3 took a dump, he had no power whatsoever. Had it towed to a diesel shop in the area. They installed a new CP3, and any necessary parts/pieces with it, including the pump mount they broke. He got the truck back, and it ran great.

Then he started to run heating oil from the tank in his house he was taking out...

He was moving some topsoil (or was it his landscape trailer? anyway) and when going for it, he would lose all sorts of power. Checked his rail pressures, and sure enough, he was down around 13,000psi under load, P0087 set. He proceeded to take it to a different diesel shop in area, as the first shop didn't change any of the coolant/fuel hoses as he told them to. Shop number two did about $400 in diagnostics, said bad injectors.

So...what did he do? Traded it in of course! Unfortunately, this truck STILL is here. The wholesaler that bought it wants it fixed.

Things the previous owner had done to the truck:

- New CP3 due to pump failure.

- New coolant pipes that were rusty. Turns out, he has an external head gasket leak. Awesome.

- Shop 1 and 2 both installed a new "rail plug" which I assume is reference to the FPRV on the driver's rail.

- Installed (then removed) a lift pump after running into the P0087 issues. For some reason, he installed it after the fuel filter housing. Pretty sure he should have put that after the tank...

- New fuel filter housing about, 4-5 years ago.

- Truck did have an Edge tuner on it, approx. for 6 years. Not too much Level 4 usage, but a lot of level 2 or 3.

What we have done to the truck:

- 8 New (refurbished) injectors. Injectors were customer provided from InjectorsDirect.com Old ones failed the return test, 19-31 mL of fuel within the test time. GM spec calls for 18mL max.

- New CP3 pump, due to Shop 1 not willing to send out the pump to be tested to see if it was good. We were hoping that if it were bad, that we could be in for at most a warranty replacement on that pump. Instead, the wholesaler approved a GM reman instead.

- New sending unit. Old one was original, quite rusty up top. Feed port on it didn't seem to flow?

- Vacuum readings to start were 5.2 in/hg at WOT before changing fuel filter.

- New sections of rubber fuel line where there was concern.

So. Injector return rates are good now with the refurb'd units.

What happens when you drive it?

We are pretty much in the same boat as the p/o of the truck. Driving like an old man, it will run great. It will run commanded fuel pressure. Any type of power demand, it will not put out more than 12-14k psi of fuel pressure. In the service bay, you can put it to the floor and hold it, it will not bog or nothing. Command the fuel pressure via a Tech 2 to 23-24k psi at idle, and the truck will do it all day long, and match the commanded value.

What possibly could be going on here!?!? Our tech is lost AF right now. Everything done to this truck does nothing in return, except we did fix the return rates (the new injectors). I have read thread after thread on here and other Duramax forums, the tech has read the Kennedy P0087 information...

Are we overlooking internal damage? Is the filter housing sucking air? Why does this happen only when driving the truck? Hot, cold, etc. still does it.

H.E.L.P. P.L.E.A.S.E. !!!!!!!!!
 

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I may be off base here but if this truck came in to my shop I would likely recommend a Kennedy twin lift pump setup and see if that wouldn't cure it. Too bad money was spent on injectors as a tune from Kennedy would have cured the P0087. Just my $.02.
 

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https://www.kennedydiesel.com/detail.cfm?ID=289 what fuel suction readings should be.
I have also had trucks with the flexible suction hose bad in the tank (rough running and P0087 when below 2/3 of a tank.
Had one with the suction line crushed during tank installation (P0087)
 

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All I can offer is that when I started getting P0087 codes, I fixed it with this plug.

 

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Discussion Starter #6 (Edited)
Idle vacuum from idle through 3000rpm stays at the 2-3 range as listed on the Kennedy site for the vacuum gauge. Under load driving, it pulls a max of 10 in/hg.

I may be off base here but if this truck came in to my shop I would likely recommend a Kennedy twin lift pump setup and see if that wouldn't cure it. Too bad money was spent on injectors as a tune from Kennedy would have cured the P0087. Just my $.02.
I've noticed that many are cured with this route.

did anybody flush the fuel system after putting in the 1st cp3 pump,and did they flush it after running home heating oil thru it
From the first pump I am not sure. After the p/o ran heating oil through it for a bit, he switched back to diesel.
 

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Discussion Starter #7 (Edited)
I cant edit that last one, but apparenty he was cutting the diesel he ran with the heating oil. I wonder though, if it was Kerosene instead of a red #2 oil. I'm sure at least a 50/50 mix. Right after he started running that is when the original pump took a dump, so I wonder if it was kerosene and it killed the original pump.
 

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10" at WOT is indicative of some type of obstruction in the suction circuit. That ain't an air leak or a bad FPRV. Either the lines are collapsing, the lines are deteriorated, or something is fouled in the pickup tube.

If you haven't pulled all of your hair out yet, run the truck off a portable tank. The quick connects on the driver's side are where to tap in. For short testing, you just need the suction side. For longer testing, you'll need to return fuel to the portable tank, too.
 

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Discussion Starter #10 (Edited)
10" at WOT is indicative of some type of obstruction in the suction circuit. That ain't an air leak or a bad FPRV. Either the lines are collapsing, the lines are deteriorated, or something is fouled in the pickup tube.

If you haven't pulled all of your hair out yet, run the truck off a portable tank. The quick connects on the driver's side are where to tap in. For short testing, you just need the suction side. For longer testing, you'll need to return fuel to the portable tank, too.
The portable sounds like the next step to eliminate the truck fuel supply system. The sending unit in the tank (looks like a fuel pump on a gas truck) was replaced with a new one.

I just went for a ride with the tech working on it for some more info. Under 48% Accelerator Position the truck will output within 1-3k psi of commanded pressure. Fuel temps get to about 130F right after a hard pull, but do cool off to 120F. At 50% APP or more, actual pressures drop to 6-10k psi less than commanded. In park, you can command the pump to 26k psi, and it will output 26k psi. Regulator command percentage is 30-35% lite throttle, and drops to 10-15% when you tip in to it. At 100% app, output pressure hit 11k psi and tripped the P0087 and limp mode'd the truck.

I find it crazy that if its lines collapsing, that its only duplicated over 50% throttle, and while driving. Runs like a champ all the other times under 48% throttle.
 

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Can you watch the vacuum during the same test driving?
 

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P0087
If these codes set only on hard acceleration or when pulling a hill with a load, check fuel supply issues first. Then see if rail pressure will reach 21,000 PSI at idle, if it does then the low rail pressure under a heavy load is usually caused by a bad high pressure pump.

Supply and Fuel Filter Housing

The fuel filter housing is on the suction side (there is not a supply pump from the factory) and are prone to suck air. 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, plugged filter, drain valve, rubber hoses and 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.

High Pressure Injection Pump (CP3 Pump)

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. Perform the injector return flow test.
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. However, the injectors are typically damaged first, but any contamination that got into the injectors went through the CP3 pump first.
3)The most common failure of the high pressure pump is the inability to keep up with high fuel demand such as towing a trailer up a hill. This problem will usually set a low rail pressure code.
4)Other Notes:
• If the vehicle has starting issues then the injectors are the most likely cause. Perform the injector return flow test.
• If the vehicle only acts up during a hard pull with a load and there are no restriction issues then it is more likely a HP pump causing the problem. A limit valve could also cause this problem.

P0087; fuel rail pressure is less than 22.5 MPa at more than 600 RPM, fuel rail pressure too low. For LLY, LBZ, LMM, see Enhanced Injector Return Flow Test above also.

1)Excessive restriction, fuel supply, plugged filter or sucking air. Install special tool J44638 to check vacuum restriction on fuel supply to the high pressure pump. Maximum restriction at WOT (wide open throttle) is 5 inches HG in park. When driving under hard acceleration maximum would be 7-8 inches Hg. If too high replace the fuel filter and retest.
2)If restriction is only a couple of inches vacuum, that could indicate that the fuel supply system is sucking air, use clear fuel lines at the filter head to check for air.
3)Excessive restriction could also cause a DTC P1093 to set at the same time.
4)Rail pressure should read 1-1.8 MPa with key on and engine off. If out of range replace the rail pressure sensor.
5)Check fuel return from the high pressure limit valve or fuel pressure relief valve. If it is leaking then it will need to be replaced. We have also heard of race plugs leaking, even if you have a race plug, you may want to check for leakage at max rail pressure.
6)With the engine up to operating temperature, use the scan tool to command rail pressure to 21,000 PSI, if the rail pressure will not achieve 21,000 PSI at idle you most likely have a problem with the injectors, Especially if you are having a hard start, miss, rough run or smoke and balance rates are excessive. Perform the enhanced injector return test.
7)Disconnect the fuel rail pressure sensor the fuel pressure should be greater than 175 MPa as displayed on the scan tool.
8)If these codes set only on hard acceleration or when pulling a hill with a load, check fuel supply issues first. Then see if rail pressure will reach 21,000 PSI at idle, if it does then the low rail pressure under a heavy load is usually caused by a bad high pressure pump.

Injectors

It takes about 2500 PSI rail pressure for the injectors to deliver fuel and the engine to start.

1)Injector return flow; maximum allowable leakage for one injector is 5 ml in 15 seconds, maximum per bank is 20 ml: check when cranking, with the FICM disabled, pressure should be 114 – 135 MPa during cranking. Specifications are for API rating of 40-44.
2)GM only provides a specification for return fuel when cranking for LB7 engines, however, we have done some testing on a good running LB7 and found that injector return flow at idle from one bank was 95 – 110 ml in one minute at 21,000 PSI.
3)Excessive leakage from the injectors usually results in a starting issue, which could occur hot or cold, but usually occurs hot because the fuel is thinner when hot. However, excessive leakage from the injectors can also cause a DTC P0087, P0093 or a P1093 to set. When using the scan tool to increase rail pressure at idle, if you can’t get to 21,000 PSI then the injectors are usually bad.
4)You can also use balance rates to help determine if you have any bad injectors. If an injector is leaking excessively into the return the balance rates are often at the edge of specification. Injectors that have a poor cylinder power contribution or a noise or smoke change when canceled will also need to be replaced and are likely to cause low rail pressure during cranking.
5)LBZ Enhanced Injector Return Flow Test- GM has come up with a test for use on the later Duramax engines. This test is specifically for the LBZ engine, but could be applied to LLY and LMM engines also.

The test steps are listed below-
1)Engine at normal operating temperature, 181-189 deg. F.
2)Remove return hoses from one bank of injectors.
3)Use adapters to run hoses off of injector returns in to individual graduated containers.
4)Run engine until fuel flows from all four injector return hoses. Then with the engine at idle, command rail pressure to 17,400 psi with the scan tool. Place the hoses in the graduated containers for 30 seconds.
5)Turn off ignition and record measurements.
6)Repeat above steps on the other bank of injectors.
7)Add up all recorded measurements to determine total injector return volume. If the return volume is less than 144 ml for all 8 injectors, refer to the high pressure pump test. If the return volume is greater than 72 ml per bank, replace any individual injector with return volume greater than 18 ml.

6)Other Injector Notes
-Balance Rates, when checked hot in drive after a hard test drive, should indicate bad injectors. Any injectors that are more than +/- 6 are a possible cause for rough run.
-Miss, smoke or rough run usually indicate that the injectors are the cause. LMM engines with a DPF may not show any smoke, but frequent DPF regen events would suggest poor combustion.
-We have seen a couple of vehicles with no starting issues, but injector return is excessive at higher rail pressures, this can cause a P0093 or P1093.
 

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Discussion Starter #13 (Edited)
Can you watch the vacuum during the same test driving?
I went with him just now. He ran a brand new 5 gallon tank out of the bed, fresh fuel from a high volume store. He plumbed some clear 1/2 line (stiff so it wouldn't kink, yet clampable). He went for the feed pipe where the lines from the tank connect to. First few minutes in the drive were fine. Then it started to act up. Under a load, fuel pressure would peak at command then fall quite quick to a lowest noted of 12,500psi. The regulator command % at first stayed in the 30-35% range, but when the truck acts up, it drops to as low as 9%. No air bubbles visible.

We did not have a vacuum gauge on at the time, but next run he will. Also, he is planning on going either direct to the filter head or bypassing the filter all together. So...new fuel source, the new injection pump, the injectors, filter, same problem still.
 

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Discussion Starter #14
Update:

Tech plumbed right to the pipe after the filter housing (the parts catalog calls in the fuel feed manifold? where the hose from the filter goes to).

No change. Truck still does the same crap. Rules out the supply side and the filter housing. He is going to see about running the feed direct to the injector pump, try and see if that "manifold feed pipe" is restricted.
 

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I don't know if this was related to this code, but there was a thread on here awhile back that after the CP3 pump went out and was replaced, the tech could not get the truck started, no matter what he did. They eventually sent it to GM and a Master tech figured it out.

After the cp3 pump went it sent metal into the fuel rail and plugged it. The normal fuel rail size to the injectors is about a #2 lead pencil size (his description), but there a restriction (the size of a needle) just before it y's off to the two banks.

Perhaps you have a partially plugged fuel rail from the first cp3 going out.
 

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Discussion Starter #16 (Edited)
Update:

Tech went back out with vacuum gauge and the 5 gallon remote supply for fuel. Vacuum under load and driving never broke 2-3 in/hg.

I don't know if this was related to this code, but there was a thread on here awhile back that after the CP3 pump went out and was replaced, the tech could not get the truck started, no matter what he did. They eventually sent it to GM and a Master tech figured it out.

After the cp3 pump went it sent metal into the fuel rail and plugged it. The normal fuel rail size to the injectors is about a #2 lead pencil size (his description), but there a restriction (the size of a needle) just before it y's off to the two banks.

Perhaps you have a partially plugged fuel rail from the first cp3 going out.
Tech is headed there next. We have a copy of the bill from the first place, I see no indication they replaced either rail or if they cleaned the system or not.
 

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Any update?
 
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