P0087 fuel rail pressure low limp under high loads

[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?

[Kennedy]

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?

I did not say that you are dumb. What I am pointing out is that you have made 2 factually incorrect statements and likely a third

1) There is no FICM

2) The pump flow at 100% duty cycle is theoretically 0

3) So how do you know the pump command is really giving all it can when the DTC is set?


The way I see it for those who face this condition there are 6 options:

1) Replace the injectors
2) ECM programing
3) Ignore the problem and reset the code on the fly as MRE did for quite some time
4) Spend hundreds if not thousands in diagnostics and parts changing everything short of the injectors because they cost most.
5)Sell or trade the truck
6) Step into in Mr Peabody's WABAC machine and go back to the day the truck was delivered. Add a lift pump, secondary filtration, and quality additive to every ounce of fuel that you burn.



FWIW the WABAC machine pre-dates me by a significant number of years bet here it is:

[rapidoxidationman]

This is an interesting conversation to me and I've been following it closely. I'm hoping the new guy won't get frustrated and quit visiting this forum cuz it does sound like he knows a bit about the dmax and could be a valuable asset here - if he can take the initiation...

I'm trying to understand just how the HPFP and related system works, given the info that's been presented by both sides of the discussion. Hopefully someone will confirm or deny what is presently my understanding:

The high pressure fuel pump is driven by the engine (cam, chain, gear, it doesn't matter). It is mechanical and directly connected so its ability to pump fuel is directly related to the engine speed.

The fuel pressure regulator does the control side of things, is electronically controlled, and does the bidding of the ECM according to load, RPM's, and requested pressures to make the injectors work properly. It has the ability to be fully closed (delivering 100% of the pressure the pump is able to put out but very low volume) or it can be fully open (essentially dropping the pump output pressure to zero but with high volume in layman's terms) but the normal range of operation is - what - between 5% and 50%?

So when the injectors (or whatever failing component) have too much free flow and the regulator has to go beyond that normal range of operation the computer gets pissed off, sets a code, and goes into limp mode.

Kennedy's solution tweaks the "normal range of operation" to something that is technically out of the engineer's specs, but allows normal operation albeit with higher flows from the regulator to compensate for worn parts.


How'd I do?

[DmaxMaverick]

This is an interesting conversation to me and I've been following it closely. I'm hoping the new guy won't get frustrated and quit visiting this forum cuz it does sound like he knows a bit about the dmax and could be a valuable asset here - if he can take the initiation...

We value the input of anyone willing to engage, with something to offer (or nothing to offer, for that matter). This is especially true of the technicians actually working in the field. We, TDP, need to do the best we can to ensure everyone is on the same page, so to speak, especially when unorthodox methods are being implemented. A $5K repair is not always the immediate solution, such as in this case.

I'm trying to understand just how the HPFP and related system works, given the info that's been presented by both sides of the discussion. Hopefully someone will confirm or deny what is presently my understanding:

The high pressure fuel pump is driven by the engine (cam, chain, gear, it doesn't matter). It is mechanical and directly connected so its ability to pump fuel is directly related to the engine speed.

The fuel pressure regulator does the control side of things, is electronically controlled, and does the bidding of the ECM according to load, RPM's, and requested pressures to make the injectors work properly. It has the ability to be fully closed (delivering 100% of the pressure the pump is able to put out but very low volume) or it can be fully open (essentially dropping the pump output pressure to zero but with high volume in layman's terms) but the normal range of operation is - what - between 5% and 50%?

So when the injectors (or whatever failing component) have too much free flow and the regulator has to go beyond that normal range of operation the computer gets pissed off, sets a code, and goes into limp mode.

Kennedy's solution tweaks the "normal range of operation" to something that is technically out of the engineer's specs, but allows normal operation albeit with higher flows from the regulator to compensate for worn parts.


How'd I do?

Essentially correct. The regulator will compensate for the failed component's (unaccounted) increased flow, causing the PCM to complain when the regulator requirement is greater than what is expected, according to the conditions. The PCM accounts for every drop of fuel through the system, and "knows" where the fuel should be going, as well as what is required of the components to accomplish that.

[dougmac]

The regulator will compensate for the failed component's (unaccounted) increased flow, causing the PCM to complain when the regulator requirement is greater than what is expected , according to the conditions. The PCM accounts for every drop of fuel through the system, and "knows" where the fuel should be going, as well as what is required of the components to accomplish that.

I don't believe this to be true and I don't understand the term "complain" as it relates to the pcm. I see no trouble codes that indicate a fault condition exists when "the regulator requirement is greater than expected" and it is not listed as a condition for setting the P0087 trouble code or even mentioned anywhere in the P0087 trouble shooting chart.

Excessive injector spillback is however mentioned as a cause.

What leads you to this conclusion?

[dougmac]

It is completely flawed logic that the pump does not pump to capacity when it sees a pressure below requested condition.

Equally flawed is the statement that it reduces output as a protection mode for the pump. There is less pressure on the internal parts because the the rail pressure is reduced under these conditions. There is more fuel flow through the pump allowing for better cooling and lubrication. This condition is a less stressful to the pump than operating at full pressure with more limited fuel flow.... I am not sure what they would be trying to protect it against?

[rapidoxidationman]

I don't believe this to be true and I don't understand the term "complain" as it relates to the pcm. I see no trouble codes that indicate a fault condition exists when "the regulator requirement is greater than expected" and it is not listed as a condition for setting the P0087 trouble code or even mentioned anywhere in the P0087 trouble shooting chart.

Excessive injector spillback is however mentioned as a cause.

What leads you to this conclusion?

I'm going to preface this by saying two things:
1) I have nowhere near the knowledge base that other members here have, possibly including you.
B) When I need to I'm pretty good at sussing things out.

BUT:
Wouldn't "excessive injector spillback" cause the regulator requirement to be greater than expected?
and
As far as the term "complain" goes, is the lodging of a trouble code not a complaint as a result of the PCM seeing something out of spec?

I'm not trying to start an internet pissing match, but there's a great deal of real world experience on this board that may not be found in a tech manual or a P0087 troubleshooting chart...

'scuse me while I go pop another batch, this time with butter...