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My Bentley 996 manual (p. 24-6) has instructions for DME adaption for ME 7.2 (996.1) and ME 7.8 (996.2). I don't think that just clearing the error codes earlier fully reset the ECU.
* It doesn't say to power cycle the ECU, but gives instructions for if the ECU is power-cycled. I removed fuse B8 for 30 seconds to remove the power to the ECU.
* Conditions:
-Vehicle is stationary
-Battery voltage is 10 to 16 V
-Engine temperature is 5 to 100 degrees C
-Intake air temperature is 10 to 100 degrees C
* Switch the ignition to on without starting the engine. Wait for 60 seconds.
* Switch the ignition off for at least 10 seconds.
I did this.
After starting the DME adaption, I ran the engine to look for vacuum leaks (which may not be the best thing to do during DME adaption).
I squeezed all of the vacuum hoses I could find to see if there was a change in the engine speed. No changes.
I sprayed propane from an unlit torch to all of the vacuum junctions and hoses I could see. No changes.
I then sprayed the aforementioned QD Cleaner, which I confirmed burns well, to all of the vacuum junctions and hoses I could see. No changes.
Twice I unscrewed the oil filler cap and the engine immediately ran rough, as seen the in plots below.
Once I pulled out the oil dipstick and to my surprise, there was no observable change in the engine running. The seal to the tube seems fine.
I have more work to do in inspecting for vacuum leaks, such as looking at the canister purge valve.
Does anyone know what the measured vacuum level should be when idling?
Two more cold starts:
* February 21: Smooth running. Problem fixed?
* February 22: Same roughness for about two minutes at the start. Not fixed; it's still intermittent.
Interesting observation:
The Durametric reports two different MAF readings:
(1) "Mass air flow (HFM)" in units of kg/hr. This is what I had been plotting previously. These values are whole numbers (e.g., 19, 20, 21).
(2) "Mass air flow," also in units of kg/hr. These values have resolution to 0.1 kg/hr (e.g., 19.0, 19.1, 19.2). This makes the curve smoother. When the engine smooths out, there is a little blip in the second MAF reading (violet curve below), but not in the first (blue curve below)
There is, however, a small downward step in the first MAF curve at this time.
Does anyone know the difference in the two MAF readings?
Couple of years ago I had a misfire on my '99 3.4. After lots of dead ends the mechanic eventually noticed a burning electrical smell near the ECU box in the rear seat. When he opened the ECU part of it was melted inside probably due to some kind of short. He's a very popular Porsche specialist and had never seen anything like it before. The part of the ECU that controlled the spark to cylinder 1 was damaged causing the misfire.
New ECU was easy to find but getting the software for a manual 3.4 wasn't so easy. Has run perfectly ever since.
Might not be your problem but worth a check (though I think opening up the ECU isn't so easy without a special tool). Hope you get it fixed.
Which brings us back to this: July 2015, 89 kmi: I was unable to get a standard Porsche X51 ECU flash, so I got one for the 996.2 X51 from Evolution Motorsports. I've noticed some hydrogen sulfide smell when I floor it and rev it up to 7000 rpm. I suspect that the flash results in a little too much fuel input at high revs, possible damaging the catalytic converters.
Have you considered that maybe the ECU flash is either incorrect, or corrupt?
Which brings us back to this: July 2015, 89 kmi: I was unable to get a standard Porsche X51 ECU flash, so I got one for the 996.2 X51 from Evolution Motorsports. I've noticed some hydrogen sulfide smell when I floor it and rev it up to 7000 rpm. I suspect that the flash results in a little too much fuel input at high revs, possible damaging the catalytic converters.
Have you considered that maybe the ECU flash is either incorrect, or corrupt?
DrMEMS, I had a stuck intake lifter on cylinder 4. Symptoms were random misfires, but typically when I went above 3000 rpm and came down to an idle, then it would misfire. Take the car out, get it nice and warm, cruise at 4000 rpm and directly come down to an idle and stop. Wait and see if it misfires. Do it a couple times and see if you can produce it. Basically what might be happening is that the lifter gets stuck in high lift, creating a mixture imbalance for idle conditions and throws the misfire code. Give it a shot and see if you can replicate the symptoms. Also the lifter issue occurred in my car at 34,000 miles, during the winter, possibly another culprit?
Good luck!
After a day of smooth running, the misfires returned when hot. I was able to force the engine to go from running smoothly to misfiring by revving it up to 7000 rpm while at a stop. When the engine returned to idle, the misfires felt severe. I captured the smoothness before and after in the graphs below.
The middle graph below shows that the ECU was not counting misfires when revved up, but did when the engine returned to idle.
The bottom graph shows the left and right cat O2 sensors before the cats (blue and green). Under normal operation, these voltages swing up and down every few seconds. When rough, the bank 2 pre-cat O2 sensor stays low, while the bank 1 pre-cat O2 sensor bounces around, but now smoothly as below.
The same graph also shows the left and right O2 sensor after the cats (red and violet). During smooth running, these are both nearly constant near 0.7 V. Under rough running, the bank 1 post-cat sensor reads a little high, while the bank 2 sensor is at ~0.05 V--way lower than it should be.
I'm not sure whether this is from a stuck valve lifter or a problem with one of the catalytic converters affecting the quantity of fuel that ECU says to inject.
"After a day of smooth running, the misfires returned when hot. I was able to force the engine to go from running smoothly to misfiring by revving it up to 7000 rpm while at a stop."
Wow, I really cannot believe what I'm reading. You revved your engine up to 7000 rpms while at a stop? You're lucky you didn't have to pick up pieces of rods from the ground...If you break your engine please don't write later that I did something wrong. I told you to find a good mechanic who will be able to identify the problem instead of trying to kill your engine doing it yourself. It's different when you drive and are in gear and different when stopped and revving your engine to 7000 rpms. You can damage your motor like that and later you will blame me...
After all this time if it was a stuck valve lifter (which usually doesn't go away and come back for such a long time) your engine would have already broke down. What you're doing now driving it everyday is slowly damaging your engine while trying to "identify the issue". Clearly you have no experience and you should seriously find a specialized shop which knows what to do and how to identify the problem.
You have a problem which is not related to the engine, but you will create a mechanical problem (if it hasn't happened already) by driving like this.
Martin and Agnes:
Thanks for your helpful posts. I have some questions.
Originally Posted by MBMotorsports
Wow, I really cannot believe what I'm reading. You revved your engine up to 7000 rpms while at a stop? You're lucky you didn't have to pick up pieces of rods from the ground...If you break your engine please don't write later that I did something wrong. I told you to find a good mechanic who will be able to identify the problem instead of trying to kill your engine doing it yourself. It's different when you drive and are in gear and different when stopped and revving your engine to 7000 rpms. You can damage your motor like that and later you will blame me....
What is the problem here? The engine was fully warmed up and as you can see, the measured temperature did not change during revving.
I revved it up to 6800 rpm; redline is ~7200 rpm. The time at high revs was less than 10 seconds. Dyno runs are done every day all over the world on stationary cars with high revving for much longer times.
Originally Posted by MBMotorsports
After all this time if it was a stuck valve lifter (which usually doesn't go away and come back for such a long time) your engine would have already broke down.
Both Macster and ChicagoSpeed996 suggested that the Variocam Plus could be stuck in high lift mode.
Also, I still have the tick-tick-tick sound at the same frequency as the camshaft rotation. I hear it much of the time (and it does not correlate with rough running). Three out of three mechanics surveyed say this sound is a sticky valve lifter.
Originally Posted by MBMotorsports
What you're doing now driving it every day is slowly damaging your engine while trying to "identify the issue".
This is bad. How am I slowly damaging my engine?
Did you notice that this is an intermittent problem? I have to run it to see the problem.
Originally Posted by MBMotorsports
Clearly you have no experience and you should seriously find a specialized shop which knows what to do and how to identify the problem.
Which shop near San Jose, California is this? As I said earlier, I don't trust the dealer. I've talked to the indy who installed the motor and he can't think of anything more to look at than what already done. There have been several posts about similar problems that other drivers had that took many different shops and a lot of money to nothing.
Originally Posted by MBMotorsports
You have a problem which is not related to the engine...
It may or may not be related to something inside of the engine. I hope it's not.
But simply declaring "it's not related to the engine" doesn't make it true. And because it's intermittent doesn't "prove" it's not related to the engine internals.
Originally Posted by MBMotorsports
... but you will create a mechanical problem (if it hasn't happened already) by driving like this.
What is the problem here? The engine was fully warmed up and as you can see, the measured temperature did not change during revving.
revving an unloaded motor that fast can and will damage a motor. Running an engine to redline loaded is fine. You can do the research yourself if you wish, but rest assured that doing that is unhealthy to a motor.
revving an unloaded motor that fast can and will damage a motor. Running an engine to redline loaded is fine. You can do the research yourself if you wish, but rest assured that doing that is unhealthy to a motor.
That's the first time I've heard that, but there's plenty for me to learn.
Curiously enough, during "Porsche Launch Control," the engine revs up to 6500 rpm while the car is stationary. See http://www.porscheownersmanuals.com/...carrera/6/155/
That's the first time I've heard that, but there's plenty for me to learn.
Curiously enough, during "Porsche Launch Control," the engine revs up to 6500 rpm while the car is stationary. See http://www.porscheownersmanuals.com/...carrera/6/155/
Weve gone OT here, but that is a 2012 motor that was designed with launch control in mind. That is apples and oranges.
02-19-2016, 04:42 PM
