nine9six

Thanks Craig...Since this is my first CEL, I will look for either consistent or random misfire codes. If consistent on the same bank (bank "2" in my case) (cyl's 4, 5, 6) might indicate the possibility of an O2 sensor; per my thoughts and Loren's validation.

If random, logic may dictate the beginnings of DMF failure, as Steve originally suggested as one of the start points.

In the interim, I will order cap and rotor as initial start points, and then progress (if necessary) to O2 sensors...
Since these sensors are 13 yrs old, does it make sense to replace all 4?

Cheers, gentlemen

Kika

roughly: went from every 1/5 drives or so times to 1/20 or 30 drives, I am kind of wagging those numbers, as I certainly did not record every time I drove the car and what happened. Also, a variety of other driving conditions changed...
I was only driving the car about 2 times a week then, and typically a 24 mile commute each time. I have not had a CEL in a little over a year now, but also, I am driving a lot less frequently.

The only reason I mention the frequency is that I think I had two different causes for the random misfire, and when it when to one cause, the frequency became less. All of this is my theory, and I have no hard evidence to prove any of it.

Kika

Do a search, but I seem to recall that 2 of the 4 are more likely to go bad, I don't remember which 2 though.

BesideTheBox

I would say that the 2 pre-catalytic converter O2 sensors are more critical to engine operation. They provide a voltage to the ECU that indicates the amount of oxygen in the exhaust gas before it hits the catalytic converter. The ECU adjusts the fuel trim based on the feedback from these 2 sensors.

The two post-catalytic converter O2 sensors also provide a voltage to the ECU that indicates the amount of oxygen in the exhaust, but after treatment by the catalytic converter. These post cat sensors are less critical in that the ECU looks at these voltages to monitor that the catalytic converters are working.

So, if you are considering new O2 sensors, get the two pre-cat Bosch sensors. In my opinion, you could wait for a CEL indicating cat failure before looking at the post cat sensors.

Lorenfb

"I know my approach is/was not very scientific, but I am hoping the LWF will completely solve the issue."

Actually, the LWF will result in a higher probability of random mis-fires because
the rotational mass of the flywheel will not help as much to stabilize the
variations in RPMs which will indicate a potential mis-fire.

"It is just a theory, but the DMF has an inner section of silicon, and when it is hotter, there is more play, enough to throw the timing off and throw a CEL."

It's not a timing issue, as the timing used is based on the average RPM
determined during a single revolution and not the instantaneous RPM
measured between cylinders. Again, it's the small change (reduction)
in RPM that indicates a potential misfire, i.e. less energy is released
during combustion (mis-fire) and thus less force on the piston reducing
that cylinder's contribution to the RPM.

Kika

Yes, my bad, I went back and read my post, sorry for the confusion. You are correct.

JB 911

"Actually, the LWF will result in a higher probability of random mis-fires"

Excepting the situation where that is the only thing left on Kika's car causing the misfires?

Sounds like Kikas car is in getting the clutch right now?

Agreed.

nine9six thanks for posting this. I'll be interested to hear if the codes jump around from side to side like csmab had or if they stay on one side.

Kika

Yes, actually the LWF and clutch were installed by my mechanic yesterday.

I will find out if the LWF causes more random misfires, or not. This is the first time I have heard of this particular "side effect". Typically the ill effects I have read about are 1. Stalling (95) and 2. Noise

JB 911

It's the first time I have heard of it too. I don't doubt it though, it makes sense if there is less mass it will be more sensitive. On the bright side, 1. If something else is not 'perfect' it is going to alert you to you that much quicker, and 2 you have a LWF

Kika

If the flywheel is accelerating or decelerating, and there is "play" due to the silicon, wouldn't the reference point tend to move, relative to the fixed pick up point, thereby altering the average?

I was told, that the wiggling reference point throws off the timing, a single mass FW would not have that issue.

If the rotational speed is constant and there is constant centrifugal force, I can see how the degree of play even if off slightly in absolute terms would remain constant from cycle to cycle (relative).

Lorenfb

"I was told, that the wiggling reference point throws off the timing, a single mass FW would not have that issue."

Right, but since there are about 60 teeths to sense in one revolution, the
timing may vary probably at most 1/2 teeth (about +/- 12 degrees). The key
point is that timing changes aren't the typical cause of a mis-fire, i.e. it's
the change in RPM from one cylinder to the next. The timing doesn't change
from one cylinder to the next cylinder instantaneously.

nine9six

Thanks guys...This is great discussion and turning into a very imformative thread!

BesideTheBox, thanks for the note on the O2 sensors...Those buggers at 4 ea (2 different part numbers) are expensive. Before cat/in cat.

As a side note, I pinged Sunset for rotor, cap, & O2 sensors quote. I was shocked when they quoted Bosch rotors (930 602 902 02) 2 ea @ $119 ea + shipping. gasp! Pelican has the same Bosch p/n for $26 ea + shipping.

Any thoughts on this HUGE price variance?

I'm not dissing Sunset, just looking for an explanation for the $90 x 2 cost difference.

Being retired and on a fixed income, I HAVE to do my shopping. A couple of bux one way or the other, and I dont bother, but this is a $180 swing on just two component parts!

Kika

Sunset deals only with Porsche factory parts, Pelican can order aftermarket parts.

There are some additional numbers following the Pelican parts number, usually starting with an "M"

I was told by Andraya, that those typically indicate aftermarket parts.

What exactly does THAT mean? I am not entirely sure. Perhaps the supplier is the same, and the part has the same form, fit and function, but maybe went through a different quality process?

I have heard that the Textar Porsche brakes have a different compound than the standard ones, so while they look and fit the same, the actual guts are a little different.

We used to buy data recording tapes for a project I worked on, we bought the ones that had more rigourous testing conducted on them, and even they they came of the exact same line as the ones that weren't tested to the same standards, they cost 3 times more due to the increased testing.

then again, you could be paying for the name on the side of the box.

Van1

I used to get random misfire codes quite frequently. There was no rhyme or reason as to which cylinders would misfire as it was different every time. Even after replacing cap, rotors, plugs, etc. Seemed to happen most often at idle, especially during track days when I was idling waiting to go out on track. After a year of getting random misfires, my clutch started to slip. I replaced the clutch with a 996 GT3 disk and the DMF with a LWF. Over 10k miles and several years later I have yet to get another random misfire CEL.

nine9six

Yes, I understood what you just stated and had since gotton off the phone with Pelican.

The Pelican reviews for the Bosch p/n rotor were outstanding, which is better than the excellent rating.

The rotor is a Bosch rotor, same p/n, same mfg, but I cannot speak knowingly as to the QA system each part was produced under.

Pelican Bosch distributor cap sells for abt $76, as opposed to the same Bosch distributor cap through Sunset for $45 ; so go figure...

There is also a $50 x 2 price difference for the two "before cat" Bosch O2 sensors.

P.S. I have smog due in Nov, so does throwing a CEL mean I have to address the drive cycles as well? How do I know if I have to reset drive cycle codes? Sorry for my ignorance...