ECU problem
05-17-2015, 09:27 PM
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ECU problem
Greetings fellow Rennlisters,
I purchased a 2003 996TT X50 about 6 months ago with 48,000 miles. At 50,000 miles, I took it to Motorwerks in Houston for a new clutch, new plugs, coils and fresh fluids all-around. The coils were not changed because the tech stated the coils looked ok.
A couple weeks ago, at around 54,000 miles, as I was driving it at 70mph in 6th, I felt a loss of power and tripped a CEL. Initially, the power was sluggish around 3200 rpm, then would suddenly surge to full boost (variocam sensor?). The CEL indicated a misfire cylinder 5, 6, and random. After hours of research here, I changed the plugs and coils myself and tested for boost and vacuum leaks. I didn't find any leaks and the plug/coil replacement didn't fix the problem. So I took it back to Motorwerks for help. They found three burned wires on the engine harness (right bank). I had them replace the harness (and a few other things that looked questionable such as a power steering hose and other coolant hoses and reservoir tank). Motorwerks also performed a compression test and stated that was ok. But the car still doesn't run properly. It won't rev past about 3500 rpm. Motorwerks think it's a problem with the ECU. Specifically, the DMU drivers to cylinder 4. I just took the ECU out and measured the resistance across each of the six drivers and read 5.94-5.98 kOhms. A new ECU is more than $2k. Motorwerks recommended I send the ECU to porschedmu repair in Florida. But, I don't want to spend another grand on a guess. Can any one offer any advice?
Thank you.
James
I purchased a 2003 996TT X50 about 6 months ago with 48,000 miles. At 50,000 miles, I took it to Motorwerks in Houston for a new clutch, new plugs, coils and fresh fluids all-around. The coils were not changed because the tech stated the coils looked ok.
A couple weeks ago, at around 54,000 miles, as I was driving it at 70mph in 6th, I felt a loss of power and tripped a CEL. Initially, the power was sluggish around 3200 rpm, then would suddenly surge to full boost (variocam sensor?). The CEL indicated a misfire cylinder 5, 6, and random. After hours of research here, I changed the plugs and coils myself and tested for boost and vacuum leaks. I didn't find any leaks and the plug/coil replacement didn't fix the problem. So I took it back to Motorwerks for help. They found three burned wires on the engine harness (right bank). I had them replace the harness (and a few other things that looked questionable such as a power steering hose and other coolant hoses and reservoir tank). Motorwerks also performed a compression test and stated that was ok. But the car still doesn't run properly. It won't rev past about 3500 rpm. Motorwerks think it's a problem with the ECU. Specifically, the DMU drivers to cylinder 4. I just took the ECU out and measured the resistance across each of the six drivers and read 5.94-5.98 kOhms. A new ECU is more than $2k. Motorwerks recommended I send the ECU to porschedmu repair in Florida. But, I don't want to spend another grand on a guess. Can any one offer any advice?
Thank you.
James
05-17-2015, 09:34 PM
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Forgot to mention, Motorwerks also tried moving injectors and also checked for boost leaks after putting the engine back in. They think when the harness melted, it shorted the DMU driver. If that's the case, shouldn't there be visible damage to the driver, and no conductivity? As I mentioned, I am reading consistent resistance across each driver.
05-18-2015, 12:26 PM
#4
Race Director
First I would avoid driving the car any more until you get this sorted.
Second, trouble-shooting the ECU is a real problem. If you do not see any obvious signs of damage at any of the bits and blobs on the boards it can be hard to know what is wrong.
Maybe someone who works on similar PCBA's have a clue.
From the wiring harness damage what Motorwerks offered as what happened makes sense.
I recently had my Boxster in for the air bag warning light being on all the time. The tech found there were no error codes associated with this warning light.
The diagnosis was a "short". Well, being a software engineer rather than a hardware engineer I wondered how could this be.
What i learned was the warning lights are all fed power through a common power line. When the DME or instrument cluster controller wants to turn on a light it activates a ground. This is I think a fail safe system in that it requires active effort on the part of the controller to keep the lights dark.
I took the instrument cluster to work and had a tech look over the board. I looked too. Everything looked just fine. Since the unit can be "rebuilt" (at a cost of $400, vs $2500 for a new one!) we didn't get too frisky with the thing.
What probably happened is the output that is the ground control for the air bag LED/light has failed and this can no longer be raised to break/disconnect the light from the ground. Because the light has power all the time it of course then shines.
I talked to the guy who fixes these clusters and he said to fix he'll unsolder the bad chip and solder in a new one.
Something like this could have happened to the DME in your car. A power surge took at the control pin's internal chip circuit and the DME can no longer control this pin.
Or possibly some intervening hardware/circuitry that is between the incoming wire and the DME, to provide an extra layer of "insulation" against just such an occurrence.
The DME rebuild service probably knows all about this which is why it can repair these.
All you can do is eliminate the other possible causes for the behavior and if none of those are the cause then there's not much left. These ECU/DME rebuilding services arise because things do happen, go wrong, with these electronics.
In the case of my Boxster I think age caught up with it. IN the case of your car, the wiring short I think played the primary role.
Second, trouble-shooting the ECU is a real problem. If you do not see any obvious signs of damage at any of the bits and blobs on the boards it can be hard to know what is wrong.
Maybe someone who works on similar PCBA's have a clue.
From the wiring harness damage what Motorwerks offered as what happened makes sense.
I recently had my Boxster in for the air bag warning light being on all the time. The tech found there were no error codes associated with this warning light.
The diagnosis was a "short". Well, being a software engineer rather than a hardware engineer I wondered how could this be.
What i learned was the warning lights are all fed power through a common power line. When the DME or instrument cluster controller wants to turn on a light it activates a ground. This is I think a fail safe system in that it requires active effort on the part of the controller to keep the lights dark.
I took the instrument cluster to work and had a tech look over the board. I looked too. Everything looked just fine. Since the unit can be "rebuilt" (at a cost of $400, vs $2500 for a new one!) we didn't get too frisky with the thing.
What probably happened is the output that is the ground control for the air bag LED/light has failed and this can no longer be raised to break/disconnect the light from the ground. Because the light has power all the time it of course then shines.
I talked to the guy who fixes these clusters and he said to fix he'll unsolder the bad chip and solder in a new one.
Something like this could have happened to the DME in your car. A power surge took at the control pin's internal chip circuit and the DME can no longer control this pin.
Or possibly some intervening hardware/circuitry that is between the incoming wire and the DME, to provide an extra layer of "insulation" against just such an occurrence.
The DME rebuild service probably knows all about this which is why it can repair these.
All you can do is eliminate the other possible causes for the behavior and if none of those are the cause then there's not much left. These ECU/DME rebuilding services arise because things do happen, go wrong, with these electronics.
In the case of my Boxster I think age caught up with it. IN the case of your car, the wiring short I think played the primary role.
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