I just had the clutch and flywheel replaced in my 2006 CS (original clutch with 172K miles on it). I now notice a strong engine vibration at 2000 rpm which definitely was not there before the repair. I'm taking it back to the shop today but was curious if anyone had any ideas? Loose or broken motor mount? The vibration is evident with or without the clutch pedal depressed.
The mechanic believes it may be a defective (new) flywheel. He's checking the car this morning. A second, less-likely source is a faulty harmonic dampener. But since that wasn't messed with during the repair it is likely the flywheel.
Got the car back again. Similar issue. Vibration at 900 rpm. Another at 2000 rpm and then rough running up to 3000. The vibration at 2k is not as noticeable as before; i only notice it when stopped and the rev the engine.
Went back to the shop. They showed me engine diagnostics (while running) that showed misfires on 4 cylinders and want to change the plugs. I'm still 7000 miles away from the change interval.
So my question is: could a broken motor mount (potential caused during the clutch repair) be to blame for the misfirings due to the knock sensor being activated? Or did I all of a sudden develop plugs that aren't firing correctly?
The knock sensor wasn't activated. It is a vibration sensor which is tuned to the frequency of vibrations arising from the onset of detonation.
The misfires are from the plugs, coils, fueling issues or perhaps issues with the VarioCam system.
A defective flywheel might (might) cause/contribute to misfires.
Well, one possibility is the defective flywheel causes some variation in signal generated by the crankshaft position sensor. This mimics the conditions of misfire: the acceleration in rotational speed expected to be imparted to the flywheel by the power strokes of one or more cylinders is too little (or too great) and this is identified as misfires.
I would want the vibration to be gone before I went on a plug replacement expedition.
However, 7K miles from the plugs' scheduled change interval is not that many miles and plug service life is somewhat dependent upon how the car is used, the quality of the gasoline, so a plug change while a bit premature is not out of the question too premature. Might mention the coils could be suspect too if the car is used in nasty weather conditions. High humid areas, areas that receive snow/ice and have salted roads are harder on coils on these cars than drier areas with less severe winter weather.
At least you would know if the plugs were the cause of the misfires.
But I would not want to live with the vibration. Based on what you write it is something that wasn't there before and shouldn't be there now.
Also, I do not get the warm fuzzies that the mechanic confirmed the FW was bad, replaced it along with the clutch hardware, and still the car has vibrations.
Last but not least, I have to wonder did some mechanic take the car out for a test drive after the 1st clutch was installed and perhaps over rev the engine? Might be worth the effort to have the overrev counters along with the timestamps of the most recent events just to see what they are...
The mechanic told me that after the first repair everything was running smoothly and he thought he had the issue fixed. I think his reasoning is that the vibrations are due to the misfires as opposed to a vibration causing the misfires. He insisted that the vibrations today were different than the ones he observed the first time I returned the car.
While I agree that it isn't unreasonable to replace the plugs 7k early I would have a better feeling about it if 4 cylinders hadn't developed the problem suddenly and in conjunction with an unrelated repair. I've never owned a vehicle where multiple plugs caused misfires simultaneously over the course of several days.
If the plugs aren't fouled or severely worn I don't want to go down the path of exploratory replacements of other components looking for this issue. I intend to use the Durametric s/w to examine what I can and go from there.
I returned to the shop to pick up my car after the plug installation and they told me that three of the coil packs were cracked (and they showed them to me) and they installed three new ones to the tune of $87 each. They told me the car ran great now but the head mechanic told me that he still noticed a "slight" vibration at 2000 rpm. They told me to settle up later and I have yet to pay for the plug replacement/coil repair. Please not that I did not authorize the coil replacement.
I drove the car to work and then home. It did feel smoother while driving but when I got home and revved the engine, the vibrations are still there and as bad as before. I called the shop and they said they had called some Porsche shops in the mean time and that those vibrations are normal for "those" cars.
So I asked why they only replaced 3 coils on a car with 173000 miles on the original ones and they told me that was all they could get from their supplier. So to eliminate any possibility that the other ones could be bad I ordered 3 from Suncoast Parts (awesome place to work with) and replaced them myself. No difference.
And in the process I discovered that the shop charged me $87 each for "genuine Porsche" coils but installed Beru coils (Beru is the supplier to Porsche, but their coils, without a Porsche name and part number, are about half as much).
So at this point I'm pretty fed up with this shop. I intend to take the Cayman to a dealership or Indy shop that specializes in them and go from there.
That seems like the most likely scenario at the moment - that doing the procedure twice in some way stressed the motor mount and caused it to fail. With that many miles, it was probably already on it's way out.
Like I said, it's the next step in trying to solve this...