Volvo Penta V6-240 Fuel High Pressure Dropping to Zero

[Biz603]

Looking for some help here. Back story:

Had a DTC 0174, Adaptive Learn Bank 2 High fault. Engine went into limp mode.
Thinking it might be an injector issue (broken/stuck/clogged), I replaced the injectors, all of them just to be safe.

After resetting the code and leaving the ECM unplugged for some time to clear the limp mode, the codes are now gone and limp mode 'seems' to be gone. However, when I run the engine past 4300 rpm the high pressure fuel pressure drops from just over 2000psi to 24psi. Targeted and Actual throttle position remain high. Again, no codes. Seems like limp mode, kinda. Left the ECM unplugged for 7 days, no codes and same issue. Limp mode still active somewhere? Hard to believe. So . . .

I checked the HPFP pressure vs rpm with the Workshop manual chart. All good up to the point of failure.

Now I'm thinking the system is somehow fuel starved at higher RPM's. So, I ran the engine from a seperate gas can/fuel source, same issue. I've replaced the low pressure fuel pumps and fuel filter (and tested the pressures, all good). I've replace the high pressure fuel pump twice, same issue.

So, unless I missed something, it's not a fuel system issue.

At this point I'm thinking there is math inside the ECM that determines the output for the Fuel Rail Pump signal to the high pressure pump. That math is made up of information from 7 (I think) sensors. Looking at all of them with the Diacom software, only the ECT and Oil Pressure sensors seemed a little off. So I replaced them. Signals look better, but still no codes, still same issue.

Tested continuity from the High Pressure Fuel Pump signal to the ECM, all good. Not opened or shorting to ground. Even put an oscilliscope on the Fuel Rail Pump signal and it looks good (PWM signal increasing with RPM's).

Open to any suggestions on what to try next.
Is there another way to reset limp mode?
Am I missing something simple here?

Thanks in advance,
Biz

 

[alldodge]

Welcome

fuel pressure drops from just over 2000psi to 24psi.

There might be to many zero's here. Fuel pressure should be 50 to 60 psi

Limp mode clears on it's own once the sensors tell the ECM all is good

 

[cyclops222]

Is his pump 1 of the pumps that had all that black paint sprayed inside of them ?

 

[harringtondav]

Welcome


There might be to many zero's here. Fuel pressure should be 50 to 60 psi

Limp mode clears on it's own once the sensors tell the ECM all is good

I had some good learning with my G5 VP 4.3 direct injection. The fuel is delivered to the rail through a two stage electric transfer pump. IIRC the low stage delivers 10-20 psi, the high stage 55-75 psi. Both stages have pressure test ports.
The fuel is sent to a cam driven high pressure direct into cylinder pump. No test port, but the ECM monitors the nominal 2200 injection pressure.

 

[harringtondav]

Looking for some help here. Back story:

Had a DTC 0174, Adaptive Learn Bank 2 High fault. Engine went into limp mode.
Thinking it might be an injector issue (broken/stuck/clogged), I replaced the injectors, all of them just to be safe.

After resetting the code and leaving the ECM unplugged for some time to clear the limp mode, the codes are now gone and limp mode 'seems' to be gone. However, when I run the engine past 4300 rpm the high pressure fuel pressure drops from just over 2000psi to 24psi. Targeted and Actual throttle position remain high. Again, no codes. Seems like limp mode, kinda. Left the ECM unplugged for 7 days, no codes and same issue. Limp mode still active somewhere? Hard to believe. So . . .

I checked the HPFP pressure vs rpm with the Workshop manual chart. All good up to the point of failure.

Now I'm thinking the system is somehow fuel starved at higher RPM's. So, I ran the engine from a seperate gas can/fuel source, same issue. I've replaced the low pressure fuel pumps and fuel filter (and tested the pressures, all good). I've replace the high pressure fuel pump twice, same issue.

So, unless I missed something, it's not a fuel system issue.

At this point I'm thinking there is math inside the ECM that determines the output for the Fuel Rail Pump signal to the high pressure pump. That math is made up of information from 7 (I think) sensors. Looking at all of them with the Diacom software, only the ECT and Oil Pressure sensors seemed a little off. So I replaced them. Signals look better, but still no codes, still same issue.

Tested continuity from the High Pressure Fuel Pump signal to the ECM, all good. Not opened or shorting to ground. Even put an oscilliscope on the Fuel Rail Pump signal and it looks good (PWM signal increasing with RPM's).

Open to any suggestions on what to try next.
Is there another way to reset limp mode?
Am I missing something simple here?

Thanks in advance,
Biz

Sounds like you have Diacom or similar. I believe the 2000+ psi direct injection pump is unregulated from what I see. It is cam driven and reaches max pressure at fairly low engine rpms. There may be a return/relief valve, but I don't recall seeing it in my manual. The injectors are PWM controlled. The millisecond opening width is controlled by ECM inputs.
High pressure dropping off is possibly a high pressure pump issue, or if there is a relief valve maybe there.
Connect your pressure gauge to the high side of the X-fer pump and watch the pressure as you increase to high RPM. If you have Diacom graph the fuel rail pressure and note the X-fer pressure when/if the high pressure rail pressure drops. If the X-fer pressure holds I'd look for an issue with the rail pump.
I get back to my manual tonight and will pass on any diagnostic info related to this.
Edit. I reread you post and you mention the code was for just one bank. The high pressure rail has a crossover line between the two bank rails. Just FYI for now.

 

[muc]

Sounds like you have Diacom or similar. I believe the 2000+ psi direct injection pump is unregulated from what I see. It is cam driven and reaches max pressure at fairly low engine rpms. There may be a return/relief valve, but I don't recall seeing it in my manual. The injectors are PWM controlled. The millisecond opening width is controlled by ECM inputs.
High pressure dropping off is possibly a high pressure pump issue, or if there is a relief valve maybe there.
Connect your pressure gauge to the high side of the X-fer pump and watch the pressure as you increase to high RPM. If you have Diacom graph the fuel rail pressure and note the X-fer pressure when/if the high pressure rail pressure drops. If the X-fer pressure holds I'd look for an issue with the rail pump.
I get back to my manual tonight and will pass on any diagnostic info related to this.
Edit. I reread you post and you mention the code was for just one bank. The high pressure rail has a crossover line between the two bank rails. Just FYI for now.

Don't think your in "limp mode" Here is Volvo's description of what your calling limp mode?

Derate 1 limits maximum throttle opening to between 40%-45%. This will result in the engine speed dropping to somewhere near 3500 rpm. This speed will vary with the size and weight of the boat. When a Derate 1 condition is set the ECM will start slowly reducing the engine RPM to approximately 3500 (if the RPM was above this point), the appropriate warning light will illuminate, and the appropriate warning horn will be sounded. If the throttle lever is not moved from its original position, and RPM was above approximately 3500 RPM, then once the active code clears the RPM will slowly return to the requested speed based on throttle lever position. If the original engine speed was below approximately 3500 RPM when the Derate 1 condition set then engine RPM probably won’t change but the appropriate light and warning horn will be illuminated/sounded.

Derate 2 limits maximum throttle opening to between approximately 30%-35%. This will result in the engine speed dropping to somewhere near 2500 rpm. This speed will vary with the size and weight of the boat. When a Derate 2 condition is set the ECM will start slowly reducing the engine RPM to approximately 2500 (if the RPM was above this point), the appropriate warning light will illuminate, and the appropriate warning horn will be sounded. This derate is a “latched event” meaning that once the Derate 2 condition is set, the engine is “latched” or locked in this mode. Even if the active code clears the only way to be released from Derate 2 operation is to return the throttle to idle. Once idle RPM has been reached (and the active code has cleared) then the throttle can be advanced towards full throttle and RPM above 2500 can be reached.

Low Rev Limit and Forced Idle are used together. Either of these derates result in the engine RPM being reduced to around 850 RPM or less. This derate is a “latched event” meaning that once a Low Rev Limit / Forced Idle condition is set, the engine is “latched” or locked in this mode for the rest of that run cycle even if the active code clears. The only way to be released from Low Rev Limit/Forced Idle operation is to shut the engine off and restart it.

Engine Shut Down
Simultaneous loss of both TPS1 and TPS2 will result in an engine shut down. This is the only pre-programmed strategy that will shut off the engine.

As you can see, derate will clear itself on key off. If it comes on you should also be getting warnings from the boats display and warning horn.

Kind of sounds like you do have a fuel problem. I would recommend testing fuel pressure like @harringtondav suggests, but I would add the low pressure side of the X-fer pump.

I think your test with the oscilloscope shows that the driver in the ECU is working right.

Your 0174 code is lean on even # bank. This is usually a "one" trip fault but can be a "two" trip fault. So maybe if you run some more, you will get another code?

If your scan tool has a recording feature, use it. With these new engines battery voltage during cranking can be critical. A recording during cranking will allow you to slow it down. And see in slow motion the voltage that the ECU is seeing. Battery voltage can be read many places, but the one that really matters --- what the ECU "thinks" it sees.

 

[Biz603]

I had some good learning with my G5 VP 4.3 direct injection. The fuel is delivered to the rail through a two stage electric transfer pump. IIRC the low stage delivers 10-20 psi, the high stage 55-75 psi. Both stages have pressure test ports.
The fuel is sent to a cam driven high pressure direct into cylinder pump. No test port, but the ECM monitors the nominal 2200 injection pressure.

Yes, that's my system. I've tested the 10-20 PSI stage AND the 55-75 PSI statge in the test ports with a guage, and the both never drop off. Measured the high side pressure at 2000 - 2043 psi (with the Diacom software, no test ports for it) before it drops off to 24 psi

 

[Biz603]

Is his pump 1 of the pumps that had all that black paint sprayed inside of them ?

Stage 1 and 2 are black, but I know nothing about paint sprayed inside of them.

 

[Biz603]

Sounds like you have Diacom or similar. I believe the 2000+ psi direct injection pump is unregulated from what I see. It is cam driven and reaches max pressure at fairly low engine rpms. There may be a return/relief valve, but I don't recall seeing it in my manual. The injectors are PWM controlled. The millisecond opening width is controlled by ECM inputs.
High pressure dropping off is possibly a high pressure pump issue, or if there is a relief valve maybe there.
Connect your pressure gauge to the high side of the X-fer pump and watch the pressure as you increase to high RPM. If you have Diacom graph the fuel rail pressure and note the X-fer pressure when/if the high pressure rail pressure drops. If the X-fer pressure holds I'd look for an issue with the rail pump.
I get back to my manual tonight and will pass on any diagnostic info related to this.
Edit. I reread you post and you mention the code was for just one bank. The high pressure rail has a crossover line between the two bank rails. Just FYI for now.

Thanks for the reply and info. Agreed, the injectors are PWM controlled.
Put in two new pumps now, same issue. They are CAM driven, but seem to be regulated with a signal from the ECM.
I believe, after looking at it with an oscilloscope, the signal from the ECM to the high pressure pump is also a PWM type signal.
No test ports on the high pressure side. Only the reading it in the Diacom software.
Not sure what the X-fer pressure is. Are you referring to stage 1 and stage 2 pressure before the HPFP? If so, these pressures don't drop off even after the HPFP pressure drops off.
Agreed, the code was for Bank 2 only and was fixed. I think, as you're alluding to, it has nothing to do HPFP failure or I'd see it in both sides. And I think the pressure drops so fast that the adaptive learning doesn't have time to 'adapt', if you will.

 

[Biz603]

Don't think your in "limp mode" Here is Volvo's description of what your calling limp mode?

Derate 1 limits maximum throttle opening to between 40%-45%. This will result in the engine speed dropping to somewhere near 3500 rpm. This speed will vary with the size and weight of the boat. When a Derate 1 condition is set the ECM will start slowly reducing the engine RPM to approximately 3500 (if the RPM was above this point), the appropriate warning light will illuminate, and the appropriate warning horn will be sounded. If the throttle lever is not moved from its original position, and RPM was above approximately 3500 RPM, then once the active code clears the RPM will slowly return to the requested speed based on throttle lever position. If the original engine speed was below approximately 3500 RPM when the Derate 1 condition set then engine RPM probably won’t change but the appropriate light and warning horn will be illuminated/sounded.

Derate 2 limits maximum throttle opening to between approximately 30%-35%. This will result in the engine speed dropping to somewhere near 2500 rpm. This speed will vary with the size and weight of the boat. When a Derate 2 condition is set the ECM will start slowly reducing the engine RPM to approximately 2500 (if the RPM was above this point), the appropriate warning light will illuminate, and the appropriate warning horn will be sounded. This derate is a “latched event” meaning that once the Derate 2 condition is set, the engine is “latched” or locked in this mode. Even if the active code clears the only way to be released from Derate 2 operation is to return the throttle to idle. Once idle RPM has been reached (and the active code has cleared) then the throttle can be advanced towards full throttle and RPM above 2500 can be reached.

Low Rev Limit and Forced Idle are used together. Either of these derates result in the engine RPM being reduced to around 850 RPM or less. This derate is a “latched event” meaning that once a Low Rev Limit / Forced Idle condition is set, the engine is “latched” or locked in this mode for the rest of that run cycle even if the active code clears. The only way to be released from Low Rev Limit/Forced Idle operation is to shut the engine off and restart it.

Engine Shut Down
Simultaneous loss of both TPS1 and TPS2 will result in an engine shut down. This is the only pre-programmed strategy that will shut off the engine.

As you can see, derate will clear itself on key off. If it comes on you should also be getting warnings from the boats display and warning horn.

Kind of sounds like you do have a fuel problem. I would recommend testing fuel pressure like @harringtondav suggests, but I would add the low pressure side of the X-fer pump.

I think your test with the oscilloscope shows that the driver in the ECU is working right.

Your 0174 code is lean on even # bank. This is usually a "one" trip fault but can be a "two" trip fault. So maybe if you run some more, you will get another code?

If your scan tool has a recording feature, use it. With these new engines battery voltage during cranking can be critical. A recording during cranking will allow you to slow it down. And see in slow motion the voltage that the ECU is seeing. Battery voltage can be read many places, but the one that really matters --- what the ECU "thinks" it sees.

Great information!! Thank you. So, I'm hearing not any kind of limp mode.
See my reply to @harringtondav above. The two lower pressure stages (which I believe are the X-fer's you're referring to, correct me if I'm wrong) hold their normal psi even after the high pressure pump fails and dropped to 24psi. Tested with a guage.
Currently I have no engine lights, warning lights/horns, or codes.
Based on your suggestions, I'll run the boat some more and crank the boat engine while graphing the supply voltage to the ECM. I'll get back to you in a couple days.

 

[Biz603]

Here's the RPM to Fuel Rail Pressure chart for this V6-240 engine.
143bar = 2074psi

 

[harringtondav]

Here's the RPM to Fuel Rail Pressure chart for this V6-240 engine.
143bar = 2074psi
View attachment 411686

Great, I see you also have the ECG diagnostics manual. When I say X-fer I'm referring to the two stage supply pump.
I've been searching the manual for an ECM pin out diagram to see where/if the ECM regulates HPFP pressure. I can't find anything. The previous page 54 states the ECM is comparing HPFP pressure to the values above pressures based on rpm. ....I'm still thinking the HPFP is a positive displacement pump that increases volume and pressure based on cam speed. Also thinking the pump has an internal relief that feeds excess fuel back into the supply hose above 3500 rpm, 143 bar/2074 psi.
You've verified the HPFP is working correctly after two replacements. My Hail Mary guess is the fuel rail pressure sensor may be quirky.
The ECM derates if the sensor pressure is >10 bar from the above table.
Continue with your high pressure vs engine rpm graphing at slowly increasing engine speeds to verify against the table. Over 4000 rpm accelerate as slowly as possible to catch any abnormalities.

 

[Biz603]

Great, I see you also have the ECG diagnostics manual. When I say X-fer I'm referring to the two stage supply pump.
I've been searching the manual for an ECM pin out diagram to see where/if the ECM regulates HPFP pressure. I can't find anything. The previous page 54 states the ECM is comparing HPFP pressure to the values above pressures based on rpm. ....I'm still thinking the HPFP is a positive displacement pump that increases volume and pressure based on cam speed. Also thinking the pump has an internal relief that feeds excess fuel back into the supply hose above 3500 rpm, 143 bar/2074 psi.
You've verified the HPFP is working correctly after two replacements. My Hail Mary guess is the fuel rail pressure sensor may be quirky.
The ECM derates if the sensor pressure is >10 bar from the above table.
Continue with your high pressure vs engine rpm graphing at slowly increasing engine speeds to verify against the table. Over 4000 rpm accelerate as slowly as possible to catch any abnormalities.

Thanks for your research and input!!
I could only find this (below) that shows the signal going to the starboard side fuel rail. I traced it out and it does. But the diagram doesn't show the red line I drew which are after that connector and plug into the HPFP. One conductor is 12VDC the other is from the ECM and is the one I put the oscilloscope on to read the PWM signal to the pump. My best guess, but I'm not sure, this signal is derived from the engine sensors (with some math) and used to supply pressure to the injectors based on the RPM vs Pressure chart. Effectively changing the displacement as needed on the CAM driven HPFP. Again, not sure.
Wondering about the internal relief valve. You could be on to something there. Is there a way to tell if the relief valve is opening? I can look and see if I'm getting a pressure bump on the supply side. Agreed, failing on 2 new HPFP's is hard to believe, but I'm desperate, I'll check it.
I will definitely try your suggestions about reading rpm vs pressure and circle back here with the results.
Thanks again!!

 

[Biz603]

Thanks for your research and input!!
I could only find this (below) that shows the signal going to the starboard side fuel rail. I traced it out and it does. But the diagram doesn't show the red line I drew which are after that connector and plug into the HPFP. One conductor is 12VDC the other is from the ECM and is the one I put the oscilloscope on to read the PWM signal to the pump. My best guess, but I'm not sure, this signal is derived from the engine sensors (with some math) and used to supply pressure to the injectors based on the RPM vs Pressure chart. Effectively changing the displacement as needed on the CAM driven HPFP. Again, not sure.
Wondering about the internal relief valve. You could be on to something there. It seems to be acting like a relief valve. It drops the pressure, then keeps the pressure dropped until the RPMs come down and the valve closes again. And because I'm getting no codes, at this point. Is there a way to tell if the relief valve is opening? Maybe I can look for a pressure bump on the supply side. Agreed, failing on 2 new HPFP's is hard to believe, but I'm desperate, I'll check it.
I will definitely try your suggestions about reading rpm vs pressure. I'll circle back here with all the results.
Thanks again!!

Just found this on the HPFP. Seems there is a relief valve, although I don't see an external adjustment screw.

View attachment 411711

 

[Biz603]

Just found this on the HPFP. Seems there is a relief valve, although I don't see an external adjustment screw.

Took the old HPFP apart looking for a relief valve set screw to set the pressure, thinking it might be set a little low. Couldn't find one.

 

[muc]

The video says the relief pressure is set by the manufacturer. Have you been getting these pumps from Volvo? I would think they would be the same pump used by GM, but some weird stuff can get changed during marinization. Agree that the chances of having 2 high pressure pumps fail exactly the same are slim. I'm usually not a fan of just swapping parts, but. About the only part you haven't replaced is the pressure sender.

Something I find strange is the only reference in the service manual to a fuel pump solenoid valve is as a possible cause for a DTC 0088 Primary Fuel Pressure High

I missed earlier that when you measured PWM, it was to the high pressure pump. Would it be possible to check power and ground right at the high pressure fuel pump? Was thinking that the solenoid might be loosing power above 4300 RPMs due to vibration in the harness?

 

[harringtondav]

Thanks for your research and input!!
I could only find this (below) that shows the signal going to the starboard side fuel rail. I traced it out and it does. But the diagram doesn't show the red line I drew which are after that connector and plug into the HPFP. One conductor is 12VDC the other is from the ECM and is the one I put the oscilloscope on to read the PWM signal to the pump. My best guess, but I'm not sure, this signal is derived from the engine sensors (with some math) and used to supply pressure to the injectors based on the RPM vs Pressure chart. Effectively changing the displacement as needed on the CAM driven HPFP. Again, not sure.
Wondering about the internal relief valve. You could be on to something there. Is there a way to tell if the relief valve is opening? I can look and see if I'm getting a pressure bump on the supply side. Agreed, failing on 2 new HPFP's is hard to believe, but I'm desperate, I'll check it.
I will definitely try your suggestions about reading rpm vs pressure and circle back here with the results.
Thanks again!!

View attachment 411711

I'm trying to invalidate my theory that the HPFP displacement is fixed. I'm mostly relying on VP's part diagrams per the attached link. I'm using my 2022 250 hp G5 engine s/n which I believe is identical to yours sans ECM.
The HPFP shown doesn't show a harness connection. But both port and starboard rails have a harness connection that I believe feeds the ECM PWM signal to the injectors.
Did your HPFPs have a harness connector? If not you may have been measuring the PWM signal for the starboard injector control harness shown.
Earlier this summer I was working with VP Sensei @muc on a full throttle range performance issue. Diacom showed injector pulse widths always below 5 ms. ...I'm thinking full power demand should be at 16-18 ms.
So unless the HPFP has a connector I'm sticking with my theory about fixed displacement/cam stroke.
When you take your next data run also graph injector pulse with along with engine rpm and rail fuel pressure. ...@muc knows Diacom like the back of his hand, so he may be able to give you better advice.

Fuel Injectors and Fuel Rails

Make sure to keep your Volvo Penta Genuine!

www.volvopenta.com

 

[Biz603]

Ok. Ramped up to steady for 20 seconds here (below):

Then, one second later:


One more second:


One more second:


You can see I was throttling back here because it was dying. It then went to idle speed.

I can do this over and over. Always dies around 4300 rpm.

Tried throttling up slow, same issue.
Tried throttling up fast, it will get to 5800 rpm and die out 1-2 seconds later.

 

[muc]

You can see I was throttling back here because it was dying. It then went to idle speed.

You maybe pulling back on the lever, but from these "snapshots" The ECM seems to be adding air and fuel.

If you look at manifold pressure, it's going up in chart 2 and has reached WOT in charts 3+4. Guessing the ECM is trying to add more air by opening the butterfly in the throttle body. If you look at TCP and TPS actual and commanded you might see more.

Now look at calculated fuel flow, It looks like the ECM is adding more and more fuel in charts 2+3 and even though it drops a bit in chart 4 it's still calling for more fuel then chart 1. If you look at injector pulse width you might see.

Hard to tell much with so little data. But (just a wild guess at this point) it looks a lot like there is air getting into the fuel system before the high pressure pump.

If you haven't yet, I would highly recommend that you take a look at cranking voltage during a Diacom recording session. Low voltage during cranking can cause some very weird things to happen in the ECM.
I have also found that once the engine gets into Closed Loop "CL+Adapt" take a look at how the fuel trims change thru out the RPMs and check the misfire counters both historic and real time.

 

[muc]

I'm trying to invalidate my theory that the HPFP displacement is fixed. I'm mostly relying on VP's part diagrams per the attached link. I'm using my 2022 250 hp G5 engine s/n which I believe is identical to yours sans ECM.
The HPFP shown doesn't show a harness connection. But both port and starboard rails have a harness connection that I believe feeds the ECM PWM signal to the injectors.
Did your HPFPs have a harness connector? If not you may have been measuring the PWM signal for the starboard injector control harness shown.
Earlier this summer I was working with VP Sensei @muc on a full throttle range performance issue. Diacom showed injector pulse widths always below 5 ms. ...I'm thinking full power demand should be at 16-18 ms.
So unless the HPFP has a connector I'm sticking with my theory about fixed displacement/cam stroke.
When you take your next data run also graph injector pulse with along with engine rpm and rail fuel pressure. ...@muc knows Diacom like the back of his hand, so he may be able to give you better advice.

Fuel Injectors and Fuel Rails

Make sure to keep your Volvo Penta Genuine!

www.volvopenta.com

I'm pretty sure the HPFP is PWM with a fuel pump solenoid valve. The wires for it are in the harness and the diagram shows a HS and LS at the ECM. This thread has been a learning experience for me. Had no idea there was a pressure relief in the high pressure side, but it makes sense because this is a positive displacement liquid pump. It could blow itself up without relief. With the OPs symptoms it would sure be tops on the list, But 3 of them?

My manual has the fuel feed pump pressures showing.

Regulated Flow Rate 40 ± 2 GPH
Regulated Pressure @ Regulated Flow 60 ± 5 PSI
Max Static Pressure 86 PSI
Internal Regulated Pressure 10–40 PSI
High Pressure Pump Max Current @ Regulated Pressure 11.5 Amps
Low Pressure Pump Max Current @ Regulated Pressure 7.8 Amps

Are you seeing something different?