Greetings all,
I have been battling an intermittent loss of power in my 2005.5 manual BRM TDI. The condition manifests itself in the following fashion: randomly (i.e. I cannot get it to assert under any specific set of conditions that I am aware of) when accelerating it feels like the ECU completely cuts fueling to the engine. When it happens, if I step on the pedal to command acceleration, there is no response from the engine (either by seat of the pants feel or by tachometer response). The engine doesn't shut off or anything like that...it just simply begins to engine brake smoothly back toward idle. 1) If I step on the clutch and downshift and reaccelerate the engine responds to the acceleration command normally. 2) OR if I coast long enough (usually 3-4 seconds) and continue to step on the accelerator pedal it usually responds eventually to the acceleration command. 3) OR if I engage the cruise control the engine will begin fueling normally and maintain whatever speed I was at at the time of cruise control engagement.
I have taken my car to the local "guru" who is stumped at what is causing the condition. After much research on this site I have attempted to overtime eliminate the conditions which may cause the ECU to cut fueling to the engine (such as overboost or a bad brake light or brake pedal switch). Like I said earlier, there are no codes associated with the condition and I currently have no engine codes per the VCDS.
I began data logging several parameters I thought pertinent to the problem on my daily drive to work and was finally able to get the condition to assert several times on one drive. I'll post the data pictures to the post (hopefully!).
The measuring blocks that I was recording when it happened include the following:
RPM, Boost Specified, Boost Actual, N75 duty cycle, Injection Quantity Actual, Injection Requirement, Cruise Control Monitoring, and Accelerator Pedal Position.
My analysis of the data recorded during the instances where I lost power is as follows:
- During loss of power there was no overboost condition.
- During loss of power there was no assertion of the brake pedal switch or brake light switch according to the CCM bits (i.e. normal expected indications)
- During loss of power there the accelerator pedal position channel indicated normal readings of my accelerator pedal request (i.e. it didn't drop to zero indicating a loss of the request signal). I could see the pedal position respond to my inputs as I cycled the pedal from zero to 100% to no avail
**What I think is the smoking gun**
1) During loss of power the ECU did not register an Injection Requirement commensurate with the Acceleration Pedal request. It registered 0 injection requirement as if I had let off the accelerator pedal completely (even though the accelerator pedal channel showed I was making an acceleration request)
2) During loss of power when I tried to accelerate using the accelerator pedal while I had the cruise control activated (i.e. I was driving down the road, cruise set, and using the pedal to speed up to pass another car and got no response to the pedal) the accelerator pedal override bit on the CCM channel was never set indicating that according to the CCM recording that I had never pressed the accelerator pedal even though I was pressing the accelerator pedal.
I think, according to the data, that there are times that the ECU stops "seeing" my acceleration pedal request even though part of the ECU "knows" that I am in fact inputing acceleration. Is this an accurate analysis? How could the ECU simultaneously "see" my acceleration request and record it correctly in the Acceleration Pedal measurement block but NOT see the acceleration input on the CCM measurement block?
Is this a pedal problem? A wiring problem between the pedal and the ECU? Or something completely different?
Thanks in advance for all your help and experience.
**Attached are pictures of three instances when the condition asserted. I highlighted in red the exact instance when the ECU would not command fueling to the engine when I depressed the accelerator pedal. I am also including a Cruise Control Switch diagram that describes the bits you should see in the Cruise Control Monitoring measurement block for various conditions.
1) Loss of Power w/Cruise Control Not Engaged
2) Loss of Power w/Cruise Control Engaged #1
3) Loss of Power w/Cruise Control Engaged #2
4) Cruise Control Switch Values
I have been battling an intermittent loss of power in my 2005.5 manual BRM TDI. The condition manifests itself in the following fashion: randomly (i.e. I cannot get it to assert under any specific set of conditions that I am aware of) when accelerating it feels like the ECU completely cuts fueling to the engine. When it happens, if I step on the pedal to command acceleration, there is no response from the engine (either by seat of the pants feel or by tachometer response). The engine doesn't shut off or anything like that...it just simply begins to engine brake smoothly back toward idle. 1) If I step on the clutch and downshift and reaccelerate the engine responds to the acceleration command normally. 2) OR if I coast long enough (usually 3-4 seconds) and continue to step on the accelerator pedal it usually responds eventually to the acceleration command. 3) OR if I engage the cruise control the engine will begin fueling normally and maintain whatever speed I was at at the time of cruise control engagement.
I have taken my car to the local "guru" who is stumped at what is causing the condition. After much research on this site I have attempted to overtime eliminate the conditions which may cause the ECU to cut fueling to the engine (such as overboost or a bad brake light or brake pedal switch). Like I said earlier, there are no codes associated with the condition and I currently have no engine codes per the VCDS.
I began data logging several parameters I thought pertinent to the problem on my daily drive to work and was finally able to get the condition to assert several times on one drive. I'll post the data pictures to the post (hopefully!).
The measuring blocks that I was recording when it happened include the following:
RPM, Boost Specified, Boost Actual, N75 duty cycle, Injection Quantity Actual, Injection Requirement, Cruise Control Monitoring, and Accelerator Pedal Position.
My analysis of the data recorded during the instances where I lost power is as follows:
- During loss of power there was no overboost condition.
- During loss of power there was no assertion of the brake pedal switch or brake light switch according to the CCM bits (i.e. normal expected indications)
- During loss of power there the accelerator pedal position channel indicated normal readings of my accelerator pedal request (i.e. it didn't drop to zero indicating a loss of the request signal). I could see the pedal position respond to my inputs as I cycled the pedal from zero to 100% to no avail
**What I think is the smoking gun**
1) During loss of power the ECU did not register an Injection Requirement commensurate with the Acceleration Pedal request. It registered 0 injection requirement as if I had let off the accelerator pedal completely (even though the accelerator pedal channel showed I was making an acceleration request)
2) During loss of power when I tried to accelerate using the accelerator pedal while I had the cruise control activated (i.e. I was driving down the road, cruise set, and using the pedal to speed up to pass another car and got no response to the pedal) the accelerator pedal override bit on the CCM channel was never set indicating that according to the CCM recording that I had never pressed the accelerator pedal even though I was pressing the accelerator pedal.
I think, according to the data, that there are times that the ECU stops "seeing" my acceleration pedal request even though part of the ECU "knows" that I am in fact inputing acceleration. Is this an accurate analysis? How could the ECU simultaneously "see" my acceleration request and record it correctly in the Acceleration Pedal measurement block but NOT see the acceleration input on the CCM measurement block?
Is this a pedal problem? A wiring problem between the pedal and the ECU? Or something completely different?
Thanks in advance for all your help and experience.
**Attached are pictures of three instances when the condition asserted. I highlighted in red the exact instance when the ECU would not command fueling to the engine when I depressed the accelerator pedal. I am also including a Cruise Control Switch diagram that describes the bits you should see in the Cruise Control Monitoring measurement block for various conditions.
1) Loss of Power w/Cruise Control Not Engaged
2) Loss of Power w/Cruise Control Engaged #1
3) Loss of Power w/Cruise Control Engaged #2
4) Cruise Control Switch Values
