P0087 fuel rail pressure low limp under high loads

[GMADVISORMT]

Welcome to the board! Your input is appreciated. The code P0087 is an emerging problem for the LBZ/LMM. Jim

Its been quite the issue here in Montana. Lots of guys pulling a lot of weight. I have two more coming in later this week for the same issue. I wish we could just reprogram these things and change the tolerances-no can do.

We recommend fuel filters every year or every 15,000 miles. That sure seems to help with many of the fuel issues on these trucks. I have seen collapsed fuel lines ONE time.

I'd recommend starting with the filter, and then spraying off that cooler. Though come to think of it, I have a gentleman that has a Duramax that we actually pulled/measured fuel return and it was high on 3/4 injectors on one side. That pretty much confirmed the issue was related to injectors on that pickup. Its a pain of a test, but worthwhile.

Hollar at me if you need assistance with bulletins, etc.

[Jeff Paxton]

Final update: This will come as no surprise to anyone, but after being delayed on trading the truck off for 2 months in order to fulfill GM's requests for hoop jumping, they say they will do nothing. After starting here on the boards with "Jessica", then being passed to "Dustin", who passed it to "April", who then finally passed it to another gal who I could barely understand so I didn't get her name, to give the "We are sure sorry for wasting your value-less time just to tell you we won't do anything about it" speech... But we're sure sorry, we're really sorry, so sorry Mr. Paxton ad nauseum.
She said, "April put in the request for cost assistance for replacing the injectors, and it was denied." I said, "So the diesel tech at my dealership concluded after analyzing the data from the ride-a-long that it was for sure injectors?" Her reply... "Um, er, a, yeah!" So after thanking her for wasting enough of my time that I will have no time to work a deal on a trade and am now forced to pull the rig back to the east coast for work with this truck in a few days, I called my dealership. I said, "Did Brent (the diesel tech) talk to GM yet?" The reply, "NOBODY from here has talked to anybody at GM about your truck yet!" I said, "Funny, they just told me Brent said it was the injectors and that they wouldn't help with new ones." The reply, "Brent says he would like to try the FPRV. But he didn't say ANYTHING about injectors." They lied.
The same as everybody here, I never expected them to do anything to begin with, but they contacted me! Insisting that I do this and that, saying that they would do SOMETHING about it. I should have told them "No thanks" from the get-go, but I am not an impolite person. It's the lying at the end that really irks me, jerking me around for what? Their entertainment?
Going to try try the FPRV replacement. I will post if it works.

[Kennedy]

The reply, "Brent says he would like to try the FPRV. But he didn't say ANYTHING about injectors." Going to try try the FPRV replacement. I will post if it works.

It's not going to make a damn bit of difference. Try a bottle test first, BUT see if Brent can follow simple logic:

1) The system makes adequate pressure (160mpa) at light loads.

2) The FPRV is a simple analog valve to protect from overpressure.

Acknowledging these facts, how could the relief valve start dumping at 16,000 psi under load then recover and work fine at light loads.

I've seen these valves fail. They don't necessarily fail, they weaken. They weaken from use as they were NOT designed to see any actual use. They are there to prevent any potential mishaps and are set well enough above the highest commanded psi. The problem is that once they weaken they flat line at pretty much the same psi.

We do a shimmed valve that bumps the pressure up higher yet. This should not be necessary, but some feel the need. The reason they activate is the lack of a lift pump and/or restricted supply causes severe pressure cycling where the pump overcorrects and the pressure spikes beyond the set point.

[More Power]

.....It's the lying at the end that really irks me, jerking me around for what? Their entertainment?
Going to try try the FPRV replacement. I will post if it works.

Not to make excuses for GM, but we all need to remember that GM is a large company - a large bureaucracy. Without a "service order number" to reference, to keep everyone on the same page, who said what will certainly get lost as the discussion gets moved around.

If a service order number was cut for this problem, and the discussion about who said what still got lost, then there's no excuse. Jim

[Jeff Paxton]

Not sure if it's the same thing, but what "Dustin" referred to as a case number was given to me and I was instructed to refer to the number in my correspondence with GM service people both on my end and in Detroit. The number was 71-1198579870

Kennedy: I think I misspoke concerning what Brent wanted to try, though maybe it makes no difference. I said incorrectly about the fprv, Brent wanted to replace the fuel pressure regulator. ??? Anyway, I replaced the fprv. The computer senses that mileage is improved, though I think it was simply that the relief valve had partially stuck open and this fuel was not actually being burned, but rather dumped during what the computer sensed as lowered economy. It is averaging 1.8 mpg's "better", closer to what I normally got before all this began, according to the computers sensors. It had definitely weakened as the limp mode became easier to trigger throughout. I think the regulator is still a valuable possibility. If the fprv has no effect, I should know soon enough and will post, but cooling temps may play a part in delaying a limp until we return to higher temps next summer. In any event, I intend to keep the board posted of any results I get, good or bad.

[dougmac]

Hello! I am new to this form. I found this a very interesting thread. I am a diesel mechanic and have my own perspective on this problem..

The first thing I check when I have a rail pressure fault on a common rail fuel system is the injector spill-back. Excessive spill back appears to be the problem most of you are facing. I see it mentioned but not being addressed. I imagine that is due to the cost of the injector replacement.

Common rail systems return very little fuel back to the tank under normal conditions. On a Duramax, if every injector was at the the maximum allowable spill-back, at an idle you would only be returning 100ml per minute to the tank.

Excessive spill back causes the fuel demand to exceed the high pressure pump's capacity. As the fuel temp increases and the fuel viscosity decreases the spill-back will increase.

I also theorize, as the spill-back increases the excessive returning hot fuel introduces more heat into the fuel tank further exasperating the problem by elevating the temperature of the fuel in the tank.

From my perspective, you may be able to mask the problem with program tweaks and beefed up coolers but in the end to really solve the issue, you probably need to address the injector problem.

Doug

[Kennedy]

Hello! I am new to this form. I found this a very interesting thread. I am a diesel mechanic and have my own perspective on this problem..

The first thing I check when I have a rail pressure fault on a common rail fuel system is the injector spill-back. Excessive spill back appears to be the problem most of you are facing. I see it mentioned but not being addressed. I imagine that is due to the cost of the injector replacement.

Common rail systems return very little fuel back to the tank under normal conditions. On a Duramax, if every injector was at the the maximum allowable spill-back, at an idle you would only be returning 100ml per minute to the tank.

Excessive spill back causes the fuel demand to exceed the high pressure pump's capacity. As the fuel temp increases and the fuel viscosity decreases the spill-back will increase.

I also theorize, as the spill-back increases the excessive returning hot fuel introduces more heat into the fuel tank further exasperating the problem by elevating the temperature of the fuel in the tank.

From my perspective, you may be able to mask the problem with program tweaks and beefed up coolers but in the end to really solve the issue, you probably need to address the injector problem.

Doug

Comments above are quite accurate and what I've been saying all along, but I will add that I have several trucks running with program tweaks that saved the $5-7k cost of replacing injectors.

[dougmac]

Comments above are quite accurate and what I've been saying all along, but I will add that I have several trucks running with program tweaks that saved the $5-7k cost of replacing injectors.

I am guessing the program tweaks prevent the PCM from reporting the low rail pressure condition and keep the engine from de-rating. The pump can only move so much fuel. Under a heavy load, it is still is not able to keep up with the demand of the injectors with the excessive leakage. The low rail pressure condition is still present.

As long as the performance is not affected significantly and you are saving thousands of dollars, I completely understand why folks would go that route rather than fixing the actual problem.

Doug

[Kennedy]

I am guessing the program tweaks prevent the PCM from reporting the low rail pressure condition and keep the engine from de-rating. The pump can only move so much fuel. Under a heavy load, it is still is not able to keep up with the demand of the injectors with the excessive leakage. The low rail pressure condition is still present.

As long as the performance is not affected significantly and you are saving thousands of dollars, I completely understand why folks would go that route rather than fixing the actual problem.

Doug

Actually that is not the case. The P0087 is still reported and I do not simply widen the parameters. My adjustments are made to the pump control in an effort to provide the increased flow necessary to remain on target.

I do alter the limp mode somewhat to make it more useable though as the way it is now can be pretty hairy in traffic on a grade.

[dougmac]

Actually that is not the case. The P0087 is still reported and I do not simply widen the parameters. My adjustments are made to the pump control in an effort to provide the increased flow necessary to remain on target.

I do alter the limp mode somewhat to make it more useable though as the way it is now can be pretty hairy in traffic on a grade.

When a low rail pressure code presents itself the FICM has already commanded the high pressure fuel pump to 100% duty cycle to attain the requested fuel pressure. The code is set when it cannot maintain the requested fuel pressure and falls 2,176 psi below that requested fuel pressure.

I am not sure I understand.....

I don't see how it is possible to increase the "flow" beyond what the pump is capable of at 100% duty cycle. At 100% duty cycle, it is at its mechanical limit.... no matter what the programming is, the FICM can only send 100% duty cycle to the Fuel Pressure Regulator there is nothing beyond that. At that point the pump is maxed out... it cannot physically flow beyond its mechanical displacement....

[rapidoxidationman]

[Kennedy]

FICM? What FICM?

I guess it's just magic or something like that.

I'm not going to get into the detail, but it has to do with expected flow which is a calculated value based on what fresh injectors are expected to deliver and return. My theory is that once the return rate plus the delivery rate exceeds the expected flow by some apparent value the ECM needs to make excessive corrections, gets upset and quits trying. This explains why it is load sensitive. Same general operating pressures, but increased delivery.

[dougmac]

I very respectfully disagree with your theory,

As a course of troubleshooting for low rail pressure problems, I generally like to observe the desired rail pressure, the actual rail pressure and the pressure regulator duty cycle. I have yet to see a situation where I had rail pressure reading below desired and the pump was not commanded to 100%. Your experience may be different but it seem illogical that the the pump would be commanded below 100% when the ecm was detecting rail pressure below the requested value.

That's my story and I am sticking to it .....

[Kennedy]

Every Dmax that I have ever seen operated within a window of about 45%-5% in fact the programming control tables for the regulator have hard coded limits of 95% and 5%.

Maybe the FICM altered the signals

[dougmac]

So you are saying the ecm is not capable of commanding the pump to its maximum output? I am not buying it... not for one second ....

[DmaxMaverick]

Just curious....

Is the FICM relevant to the model year(s) in this discussion?

[Kennedy]

Just curious....

Is the FICM relevant to the model year(s) in this discussion?

No it absolutely is not.

[dougmac]

Just curious....

Is the FICM relevant to the model year(s) in this discussion?

Its not... if you didn't catch on, its a dig at me...

I guess asking how you use a software change to get more volume out of a pump that is already working at is capacity poses a problem.....

[Kennedy]

When a low rail pressure code presents itself the FICM has already commanded the high pressure fuel pump to 100% duty cycle to attain the requested fuel pressure. The code is set when it cannot maintain the requested fuel pressure and falls 2,176 psi below that requested fuel pressure.

I am not sure I understand.....

I don't see how it is possible to increase the "flow" beyond what the pump is capable of at 100% duty cycle. At 100% duty cycle, it is at its mechanical limit.... no matter what the programming is, the FICM can only send 100% duty cycle to the Fuel Pressure Regulator there is nothing beyond that. At that point the pump is maxed out... it cannot physically flow beyond its mechanical displacement....

For clarification there is no FICM as mentioned above.

There is no 100% duty cycle to the pump. Additionally, 100% duty cycle would be regulator completely closed and 0% duty cycle would be wide open.

[dougmac]

For clarification there is no FICM as mentioned above.

There is no 100% duty cycle to the pump. Additionally, 100% duty cycle would be regulator completely closed and 0% duty cycle would be wide open.

Ok... I concede ... I am dumber than you..

Now explain in simple terms that a dumb guy can understand. How you use a software change to get more volume out of a pump that is already working at is capacity?