mklein9

Yes, jump point voltage went down as low as 12.2 with the DVM attached, and (at least based on a glance through the back window) the dash voltmeter agreed. I've checked the dash voltmeter against the battery voltage a number of times and found it is very accurate, maybe within 0.1 V when I can get that resolution against the lines on the gauge.

The low voltage is of some concern, but it was 12.2 only for a short period right after I turned on the rear defroster. It mostly stayed around 12.5 while loaded with AC and defroster. When throttle was blipped it always rose to something over 13, maybe 13.2.

In the back of my mind I am thinking I may not be out of the woods yet even with a new CPS. However, the CPS failure (very low output) occurred over a range of voltages and RPMs even when I blipped the throttle. But what could cause a persistent low voltage with those excellent drop measurements is beyond me. Of course, the correct data will always show.

mklein9

BTW Ahsai, you say you have a 997 shifter. We got my wife an '05 Boxster last year which had a B&M short shifter installed and have the 987 original shifter. I've done some research and it appears that this shifter is compatible with 987, 997, 996, and 986. If so I was thinking about maybe using it for my '02 996. Would you recommend that?

One of my cats appears to be gone (something I discovered at my indy's last week as he ran the PIWIS on this issue). I may need a replacement and Gert's option seems like a good one. Gert supplied my car's X74 as well, although to the PO, not me. The X74 is just completely awesome.

Ahsai

As long as you have 13v or higher most of the time, you should be fine. The battery won't be charged at anything below 12.8v.

What's the p/n of the 987 shifter? If it's the same as the 997 shifter, I will highly recommend it if you're looking for much tighter shift and slightly shorter throw. I love the 997 shifter and
I had the 996 porsche ssk before. I didn't like the notchiness of it.

Oh yea, the x74 is just awesome, totally transformed the car. If you get Gert's sport cats and the Fister's mufflers, our cars will be like twins down to the side skirts

mklein9

I think I'm OK with the voltage. With all this diagnosis the car has been idling for hours over the last week and it starts up with a full force crank no problem at all. That was not at all the case before the last alternator replacement. I think it's fine but once the new CPS is installed and I drive for a week or so I will know.

Re: shifters, everywhere I look I see that 986, 987, 996, 997 shifters are all compatible with each other. The B&M short shifter kit box lists all the above models as compatible. Somebody on the Pelican Parts discussion forum also answered with an unequivocal "Yes" when asked the same. The 987 shifter I have does not have a p/n on it that I can find. Anyway, I think I'll plan on making this update when I get a chance.

Ahsai

I checked for you on www.autoatlanta.com Indeed the shifters are exactly the same across those models you mentioned. You should be good to go.

Ahsai

Just to add a data point, these are my ('03) camshaft and camshaft waveforms. My crankshaft signal is 10-15v p-p.

Yellow is the camshaft waveform and cyan is the crankshaft waveform. Note the camshaft waveform actually is not a uniform square wave pattern but rather the whole cycle is like short, short, long, long.

mklein9

New CPS arrived overnight shipment on Tuesday morning and I installed it within 30 minutes. Now it's Friday and the car has been running flawlessly. I think the problem is fixed.

Ahsai, great images there, and good reference points. I hope this thread shows up on a variety of searches for similar kinds of symptoms.

JMLavoie

Superb work, guys!
Great learning here!
Merci beaucoup!

Ahsai

Congrats on fixing the problem. Yours and mine seem to be the very first Porsch 996 CKP and CMP waveforms in the wild Hope it will help future users.

Thanks. It's fun probing the DME haha

mklein9

Update.

While I thought the new CPS fixed the issue, it didn't. Each time I have improved the car somehow, the misfiring problem receded somewhat further into the background, but would come back with a vengeance under certain circumstances as I described early in this thread. Heat or time, or some combination, would bring back the massive misfiring on all cylinders and the P0336 code (Ref mark sensor, i.e. crankshaft position sensor) thrown.

This problem having been present from the moment the car came off the truck from Flat6, Jake Raby has been extremely helpful, well beyond reasonable expectation. We have had probably 100 emails back and forth; Jake even brought Tony Callas in to help. The theories were all the way from "what, a fourth CPS?" to fuel tank venting problems to shorted CPS wiring harness to fuel pressure problems to low voltage due to an under drive pulley installed by Flat6 to help out with track use. But none of these checked out after further investigation. A dozen Durametric logs were taken and forwarded to Jake and Tony, and there was no smoking gun.

This weekend Jake and Tony were teaching an M96 101 class nearby and they asked me to bring the car up Saturday evening. Imagine me driving, Tony in the passenger seat wrestling with Durametric, Jake in the back seat, and the car jerking us all around with the misfires. Every once in a while I'd stop and Tony would jump out and adjust the gas cap or the EVAP regen valve or something. It was probably pretty hilarious. Tony concluded pretty quickly that the misfiring was so violent that it was not a fuel, leak, or vacuum issue, but had to be something like a sudden ignition adjustment or momentary ignition cutout.

After some time of complete befuddlement it was either Jake or Tony, I don't remember who (I do but the other guy is too embarrassed to let this out) thought of a scenario that would explain it. I decided to leave the original flywheel and clutch in because they were in good shape but of course partly worn (the car has 42k miles). The car was then placed on the truck for the ride back, 2300 miles. If the trucker left the car in first gear then it is possible that the bumping along the ride stressed the flywheel enough to damage it so the CPS loses the signal from the flywheel teeth, the ECU gets confused momentarily, and the engine bucks like crazy. And the P0336 code would get thrown.

Jake has arranged for a mechanic to help with this in a creative win-win way :-). I will get a new flywheel and we will carefully evaluate both old and new to see if this is a likely cause.

Further updates when I know more.

Hats off to Jake for sticking with this even though his responsibility ended when the car was put on the truck. We all hope this is finally the right diagnosis.

One lesson: when the DME throws a code, it's usually on target, or really close to it.

Flat6 Innovations

Mike is a trooper, and a very smart guy. Tony and I are both baffled by the symptoms and the inconsistency of the occurrences.

We'll learn from it.. Its not everyday that a guy works on a car 2300 miles from his shop :-)

Ahsai

Sounds like some good progress. For that code, the flywheel is the next logical suspect anyway after ruling out the CPS and wiring. One thing I don't understand though, the flywheel teeth are not touching anything so why would towing the car damage them? Or we're talking about the springs inside the flywheel damaged by towing? Very curious to see what you guys find.

Flat6 Innovations

You must not clearly understand how a flywheel can create misfires.. As a flywheel ages the second mass loses control and will allow radial fluctuations that can create this issue. I have a special tool from Luk that is uesd to measure the radial movement of the flywheel to determine it's condition.

With the car being shipped in gear for over 2,000 miles the movement on the truck was banging the flywheel and could have easily killed it or taken it far enough out of range to give this issue. Leaving a car in gear during transport can kill all sort of components and can even make the engine jump valve timing. We go to great lengths to ensure this doesn't happen, but it still does from time to time.

I have an attendee of my class this past weekend who is in Mike's area and will pull the flywheel and ,easure it, then replace it. he will then send me the flywheel and I will measure it with my same special tool to see how much is has deviated from when my work was done.

Dual mass flywheels can go bad like this and cause misfires even without aggrevation. We solve phantom issues with a flywheel replacement all the time. With Mike's car nothing made sense as it was perfect when I loaded it on the truck and it was horrible immediately after it was unloaded. The only real common denominator is the flywheel and the potential shipping damage.

Its all on my dime, several thousand dollars worth. I do whats required.

Ahsai

That's interesting info to know and kudos to your dedication to get to the bottom of this and pay for it too.

A question about the construction of the flywheel. Are the timing teeth, starter gear ring, and the center flange (shown in this photo) welded together as a single piece and bolted onto the crankshaft? https://rennlist.com/forums/11360135-post3.html

Then the second mass is on the other side of the flywheel coupled to the first mass via springs?

mklein9

I did some research on these two points and found out:

1) It appears to be normal practice among auto transport guides to tell the driver to put the car in gear, generally first gear. Presumably the trucker is more concerned about making sure the car physically gets to its destination than about damage that might occur internally. It is difficult to get references on this and I am not sure I got representative ones; I found 3 web pages from transport instructions in the UK, a page on ehow.com (which in my experience is hugely unreliable), and an Abu Dhabi transport company. Although Flat6 insists on keeping the car in neutral during transport, that may be against the trucker's policy, insurance, or whatnot.

2) A dual-mass flywheel is, as mentioned here, actually two flywheels rotating together but allowed to move radially from each other slightly by springs between them. These springs absorb rotational shocks from the engine before they are transmitted to the transmission, wheels, and chassis. However, these shocks, which are the changes in angular velocity of the crankshaft, are picked up by the ECU from the CPS signal. As each cylinder compresses or fires in turn, the crankshaft slows down or speeds up. The ECU, through the CPS signal, detects an orderly sequence of these rotational speed changes as correct cylinder firings. If they do not occur as expected, the ECU starts throwing misfire codes (P030x), and if the signal's integrity is questionable or far from expected, throws a sensor code (P0336).

As Tony was able to narrow it down, my ECU was throwing P0336 almost instantly after clearing it once it was in bad shape. When run long enough under these conditions the P030x misfire codes were also thrown (they are accumulated for a longer period so don't show up instantly and only when really bad).

The car drives perfectly when cold, and when on the freeway at higher and consistent RPMs (and airflow). It starts acting up after coming down to idle for a while when hot. Whether the trigger is heat, time, or idle is not known. As Jake described, idle is an unstable state for the car and could provoke failure of a marginal part that is sensitive to sudden changes in angular velocity.

This all lends credence to the theory that the flywheel itself is at fault. It could be damaged in shape or position, springs broken, weakened, or acting inconsistently, or something else. We shall see.