Johnnyceesred

Just a "far shot" from my yesterday experience with similar problem...

- the car is a MY06 987 with a 3.6 997 engine installed (!)

- car developed very bad idle from noticeable shaking on the wheel to detonation and engine stall within 5 days and 500 miles (all started when weather turned cold)

- CEL light kept coming on after a few minutes of idle, giving every code from 300 to 306 (random misfire and all cylinders misfire)

- checked with generic OBD readers and later with Durametric, found that MAF reads way lower than it should be, while ignition timing going crazy between -4 and +11 degrees

- replaced MAF, replaced all spark plugs, replaced one coil pack, replaced air filter, removed and checked throttle body, whole intake tubing, checked exhaust with tailpipe sensor (obviously very bad values everywhere, 700ppm CH or so...), checked both valve lifting and valve timing electronics - still no joy.

We were preparing to remove the engine when "just my 2c's" removed the breather hose between the oil separator and the intake manifold (the thicker one). Closing the hole on the intake manifold cured the problems - and later found that the :censored: tube developed a very thin crack on the lower side. Unnoticeable otherwise but the vacuum probably sucked it inwards and opened up the gap. This way air could get into the engine passing by both the MAF and the throttle valve, but only when there was enough vacuum from the previous engine revolutions to open the gap. Hence the jumpy-detonating-CEL-throwing idle... :lightbulb:

Hi and thanks for your reply.

Did the misfire move from one bank of cylinders to the other bank as mine did?

As the engine's now totally dismantled it will give the independant specialist a chance to inspect all tubes connectors etc. Our collective worry is the state of parts of the one crank block half as seen in the first thumbnail on my last post. My hope is that an authoratitive technical specialist from Porsche GB or maybe even Stuttgart if necessary, will come out and view the engine in its current state and give us a verdict on what he/she sees. I also spotted some further gouging in another part of the engine casing but we're not sure whether this was done at the factory to remove some imperfections in the casting or for some other reason.

Anyway I'll let you know more as things develop.

Best regards

John

Hope everyone had a good Christmas and Happy New Year to you all.

The engine has been dismantled and there are some concerns about the crank block.

1. Some striations have been found on one half of the crank block as if something has gouged out metal from parts of it.

2. There are cracks in the steel elements of the crank block.

3. The profile of the steel elements of the crank block differ between the two halves.

I'll attach photos to illustrate the above.

We're not sure whether these symptoms are the cause of the original misfire or additional to it. I'll report back on further results when more is known after the New Year holiday.

Best regards

John

Thanks for the 2 latest posts. The engine's out and in an almost dismantled state. Some evidence has been uncovered regarding corrosion in the connecting rods in the engine block. Will know more and report back (maybe with photos) between Christmas and early January.

Happy Christmas to all members and a good New Year.

Rgds

JCR

B-man and Scouser,

Thanks for the replies. I'll keep the thread updated with progress on mine.

The main challenges have been to find out what's causing the misfire given we've had 2 different diagnoses from 2 OPCs (1st one was a coil pack failure, hence all 6 coil packs were changed considering the high mileage, and the 2nd was misfire on cylinder 6) and why the misfire moved from one bank of cylinders to the other 2 days after the 2nd PIWIS diagnosis.

Rgds

JCR

Johnny, sorry to hear about your problem. I hope it turns out to be something simple. Anyway, please be sure to let us know what becomes of this. Cheers.

Thanks for your thoughts. The engine's being taken out of the car today as when the sump was inspected a small fragment of "white metal" (Bebbitt Metal) was found and this could be off the Intermediate Shaft Bearing. Won't know for sure until further dismantling.

The OPC where I bought the car from did say that they had experieced a misfire moving from one bank of cylinders to the other caused by swarf getting into the tappets. However this was on a brand new car and they wouldn't expect it to happen after 118,000 miles unless it was a component breaking down.

So whether the two are linked and this has resulted in the moving misfire, we'll have to wait and see.

Rgds

JCR

I have an ongoing thread on the Porsche Club GB Website. The thread title is "Mis-fire Problem".

http://www.porscheclubgbforum.com/tm.asp?m=242384

The first entry is below. I've had some very useful comments from fellow club members and thought it might be useful for reference here and any comments the Renntech forum members might have. The latest entry on the thread confirms that the engine is being taken out for deeper level investigation and hopefully a fix.

Mis-fire problem.

I would be grateful if anyone one would comment and/or give me any advice regarding the problem below. Apologies if it appears somewhat verbose, but I felt that if I missed anything out, the full picture would not be understood.

I have a 2003 996 C4S and current mileage is 117,907 (114,071 of those done by me as it’s a business car). The car’s been serviced at the relevant mileage intervals. No running problems have been encountered until the last 10 days.

On the first frosty morning of this autumn (November 1st) I started the car and immediately noticed unevenness in the engine performance on tick over. The car vibrated as if there was an imbalance in the number of cylinders firing and the “Check” warning light came on as well as the “Drive to Workshop” message. On listening to the exhaust note there was a distinct “chugging” and intermittent “pop” from the nearside exhaust. The offside exhaust sounded normal. When the car was driven a short distance however, the performance did not seem to be impacted but the “lumpiness” and “chugging” persisted on tick over.

Upon underside engine inspection, a faulty coil pack was suspected. Subsequent diagnosis at an OPC indicated a coil pack problem. The condition of one coil pack was particularly poor and others were showing the signs of splitting, so all six were changed on November 3rd. It was noted at the time the work was done, that the nearside exhaust showed more emission deposits than the offside one i.e. it was blacker

All seemed well until the same symptoms, or be they not quite as severe as when they first appeared, recurred the day after the coil packs were changed. Again the performance under normal driving did not appear to be impacted. After some miles being covered the check warning light went out. This resulted in a second visit to another OPC on November 8th. The diagnosis this time indicated a problem on cylinder number 6. Consequently a different coil pack and spark plug for the cylinder were tried but the diagnosis persisted. The suggestion was that it could possibly be a broken valve spring but this I believe does not fit in with the problem being an intermittent one and only being noticeable on tick over. Whilst driving home, around 120 miles, the warning light and message did not appear but I did notice on a couple of occasions when I braked for a junction the “lumpiness” recurred but then cleared upon acceleration.

The charge from the alternator/battery connection has now been tested as part of the problem diagnosis and has been found to be below the power reading expected. It is thought that this could be having an effect on the Engine Management System and hence causing an engine malfunction e.g. causing a cylinder/cylinders to run too rich.

The other odd thing now is that the offside exhaust outlet is now blacker than the nearside one. Also when I put my hands close to the exhausts I get the impression that the offside one is running hotter than the nearside one. Photos are attached.

I’d be interested to find out if anyone has had similar experiences and would appreciate any replies that you are able to post.

Regards

John C