P0087 fuel rail pressure low limp under high loads

[DmaxMaverick]

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.....

I don't think it was a dig at you.

Anyway, I think you are limiting the scope to only what is available within the allowable envelope of the vehicle calibration, and discounting the physical capability of the HP pump. Technically, a true "100%" duty cycle of the pump would likely see it destroyed in a very short period (unless #2 Diesel were infinitely compressible, but it's not, so....). The pump itself is "dumb", only varying its output according to the flow control, which is controlled by PCM commands, according to sensory data input and programmed demands. The operating envelope of the pump is determined by the calibration parameters, not the physical capability of the pump. Demanding a 100% duty cycle of the pump is only commanding the full duty cycle allowed by the calibration, and not, necessarily, the full capability of the pump (otherwise, the upper threshold of the pump's performance would have to be identical from pump to pump, vehicle to vehicle, under every conceivable condition). It's comprehensive, according to dozens of channels of sensory data. The PCM doesn't know, and doesn't care, what the physical limitation of the pump is (unless it's incapable of answering mechanical demands, not according to calibration parameter demands). The FPR/FRPR is limited only by the vapor, AKA: the PCM, via the vehicle calibration, sensory data, emission system control, and powertrain performance demands. Moving the operating envelope (range) of the pump performance sensory data, such as John is suggesting, is nothing more than that. Simple, and perhaps a band-aid fix, but it works often enough to make it a viable solution, if only temporary. The alternative is to pony up a few grand for a repair that may not be necessary for years to come. If it doesn't work, the only loss is a little time.

[dougmac]

Generally the high pressure pump does not produce its full volume because it is regulated by a pulse width modulated solenoid. It will increase and decrease volume as the demand changes. The only time you would see it at full volume is when it has fallen below the commanded pressure.

If it cannot maintain the requested pressure the system will log a code and derate the engine.

[DmaxMaverick]

Generally the high pressure pump does not produce its full volume because it is regulated by a pulse width modulated solenoid. It will increase and decrease volume as the demand changes. The only time you would see it at full volume is when it has fallen below the commanded pressure.

If it cannot maintain the requested pressure the system will log a code and derate the engine.

If that's the case, then why is it 9 generations of Duramax calibrations commanding 95% duty cycle all produce very different pressure and volume parameters? If you are correct, then all of them at "maximum duty" would all produce the exact same pressure. As you suggest, it's the PWM that limits the pump output, not its absolute physical capability. The problem isn't the pump, but the other end of the fuel rail. The root cause of this discussion is the sensory data failing to report acceptable fuel usage accountability, for whatever reason. Addressing a functioning pump is talking to the wrong end of the horse. This was never a pump problem. Although the problem is almost always the injectors, it was never as prevalent until the calibration parameters were changed. Same pump, same injector performance, same fuel pressure and volume regulation means. So, why wouldn't it be reasonable that a PCM calibration adjustment just might correct the condition in many cases?

The injectors in question are suffering the same exact failures as previous and later series. The component interoperability hasn't changed. The only difference is when the PCM perceives them to have failed, and will demand correction (SES lamp, limp mode, etc.). The pump isn't failing to perform just because the PCM says it is, and neither is the remaining fuel system components. No more than they have with any other series.