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benaslan

P0300, P0303, P0305, P0306-Misfire at cold idle only

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Just noticed that your actual cam angles are close to 0 the whole time. According to this thread http://www.6speedonline.com/forums/996-turbo-gt2/260463-anyone-durametric-996t-ten-minutes.html (posts #1 and #2), looks like they should be closer to 30 degree for both banks at cold start during the 1st minute. Were the logs above taken as soon as the engine started to run?

Concur with Silver on checking the fuel trim values (TRA and FRA).

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Yes, you also definitely want to check those cam deviations closely to make sure they are within spec. Could also be related, I believe, to a variocam solenoid as I believe variocam is activated at idle speeds and you said this is only on idle. Definitely check the bracket that holds the actuator. Checking these and the fuel trims should tell you a lot.

Edited by Silver_TT

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I've had a hell of a time getting the Durametric to log on start. It crashes on me and then I have to start over. Then it's no longer cold... Finally got it and the attached file shows the same thing as in the thread you mention.

I did not get TRA until awhile down in the log because it wasn't called that in Durametric, but it shows eventually.

You see the crazy number of misfires on cyl 3 & 6 (25 & 38!!!) at the high rpm warm up and then it resets.

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The fuel trims and cam angles seem to look fine. Coolant reading is fine? You have misfires even 12min after start up so it seems not just at cold start.

Edited by Ahsai

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Yeah, I asked the shop a few days ago which ones they used:

The coils are Beru part # 997 602 104 00 and the plugs are Bosch part # 999 170 195 90

I am certainly not sure if they were gapped properly, but I'd rather rule everything out before going in there. If only they were easier to get to!

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Yeah, I asked the shop a few days ago which ones they used:

The coils are Beru part # 997 602 104 00 and the plugs are Bosch part # 999 170 195 90

I am certainly not sure if they were gapped properly, but I'd rather rule everything out before going in there. If only they were easier to get to!

So did you have misfiring problems before the coil and plug change? If so, probably the new parts are not the culprit.

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64,000 miles. Problem has been around intermittently since around 37,000. Started off just occasional, like CEL light briefly once a month or so, would clear itself. Never any driveability issues. I was told not to worry about it and the part would eventually go out and the problem be known...

Now that may happen eventually, but the light is on more often than not at this point and I can't handle it anymore.

Still no driveability issues as far as I can tell.

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Looking at the fuel trim and cam data I agree Ahsai its within spec. I have seen this issue with exhaust valves not seating properly. It is more apparent when the motor is cold. you might have some carbon buildup on the valves. Since you have changed the coils and plugs and still misfiring on 3&6 I would run some Techron in your fuel system. The only way to really prove the root issue is with a pressure transducer and a oscilloscope. I have been running in to this issue a lot lately on low mileage cars that dont get run hard enough to clean them out. However the last car I diagnosed ran two tanks of fuel with Techron and lucked out not having to do a valve job.

Edited by binger

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To be honest, I think you need to get JFP in PA to chime in here if you can get his attention.

We have been over the "usual suspects": You fixed the gas tank leak issue and there are no other codes except these misfires. You already replaced the plugs and packs. You said you are comfortable with the cam/timings, and have checked any issues possibly related to the variocam. You said the fuel trims are good. I would just check and double check your work on these to be sure you are comfortable that they have really been eliminated. If I'm not mistaken, if it's not something above you could have a more serious problem. Like I said, the Mezger isn't invincible but it's a **** good engine.

Given some of the stuff you are saying, it's really hard to say for sure without actually being able to see it, but it sounds possibly related to variocam to me (eg. actuator).

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Yeah, I think I just need to get in there and check the variocam bracket. If both sides aren't broken, then I think I'll replace the plugs again to be sure myself.

If not those, then things I may try and have noticed in oth threads:

O2 sensor, even though no errors, (although I just did pass my smog test by a mile, so not so sure about that)

Fuel filter

I'm ruling out major issues since the problem is only at low rpm. Anyone have any idea how many misfires I need for the CEL to go on? Gotten up to 38 on a cylinder and no CEL for 2 days now.

If I do go in there for the variocam bracket and plugs, anything elsei should look at or do since I'm there?

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Don't think it's the O2s because a problem here should show-up in your fuel trims. If you want to make sure your O2s are working, these values can be logged in Durametric.

I'm not a practitioner so I'm not sure how often a batch of plugs can be bad (in your case it's not just a single plug). I would think this is very rare for Bosch, which are good plugs. But anything is possible.

As you are, I wouldn't sit on this if it were a variocam issue. In theory if your timing is off it leaves open the possibility that there could be valve/piston contact. Someone can double check me and look in the manual, but if memory serves the 996TT variocam is activated when the engine oil is cold at idle speeds. Please verify this, but this is one of the things making me wonder if you could have an actuator that's not 100%. I really think you need to look at that bracket. Anyway, I'm not sure but I think only the intercooler needs to come off....so it's not like you're dropping the engine. Can't really think of anything I would do while the intercooler is off unless you're interested in welding a few of the coolant lines.

Edited by Silver_TT

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My thought isn't that the plugs would not be bad, but either not tightened correctly, or not gapped correctly. Plugs are Bosch, coils are Beru. The Indy shop I use, the main guy was out when I brought it inand his new junior guys did the work and since I have no way to guage their quality, I have to say there is a chance.

Would a bunch of plugs not gapped correctly do it?

What if the fuel cap was the main issue and the ECU just needs to be reset. That a possibility?(by disconnecting power and waiting)

And yes variocam is obviously a high possibility. I've been tracking the numbers the past 3 days now and while the cam deviation numbers are all within spec, they are all very different every time. I'm guessing that's not so normal?

Edited by benaslan

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Yes, those are good brands on the plugs and coils -- should be fine. I mean, possible they didn't torque and space the plugs correctly, but given that you said you had this problem for years before those were ever touched I'm wondering how likely that is. If that were the case then, yes, it could cause misfires. Just doesn't seem like the most likely cause.

Don't think the ECU needs any more time. The fuel cap was presumably not air-tight before you replaced it and that's why the error went away after you did. My thought was that this leaky cap could have caused unmetered air to enter into the system and make your trims too lean as RPM increases -- therefore causing misfires. I would think that once you fixed that problem with the cap anything related to this issue was over then on the spot.

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Agree with Silver's thinking. Nothing much to add. The only thing is the cam deviation is still varying 10min into engine warm-up. I understand the actual cam angle changes all the time but you would think the cam deviation should not. On my car (M96, non-Turbo), the cam deviations remain the same regardless of rpm once the engine is running, even at cold start. They do change a little bit though across start ups (max +/- 0.2). Maybe the cam deviation jitter behavior is specific to Turbo engines but I can't exlpain why they should though.

@Binger: would a leak-down test reveal the valves are not sealing due to carbon deposit or it's too small to be detected but yet can still trigger misfires? Also, if the carbon buildup is on the exhaust valves, will techron still be effective given it's injected on the intake side?

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Hi Ahsai,

Only dynamic leak-down testing with a pressure transducer and a oscilloscope will reveal the valves are not sealing. It will also show you if the cams are out of time. I put a few links about pressure transducers and a oscilloscope testing below. It is very fast and powerful tool take a look. As for techron it is hit and miss however I have seen it help in the short term.

On a side note. You will start seeing a lot of carbon issues coming up on all direct injection engines from every MFG in the near future. We are seeing valve jobs at 50k however the MFGs are trying to sweep it under the carpet. Lexus is one just pays for it under warranty and dose not tell the customer. GM, BMW, VW, Ford are trying to get to the bottom of how to solve it. I went to a drivability update training class a few months ago that focused on direct injection carbon issues.

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Thanks, binger. Yes, I understand the pressure transducer + scope analysis. However, most shops are not equipped with the knowledge and equiement hence my question on a simple leak-down test.

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Unfortunately simple leak-down tests wont show you this detail. the only way your going to see it is in the waveform. Most shops that do not have the hardware or expertise hire mobile dianostic guys like me to help. The dealer will just sell you a valve job and be done with it.

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I'm curious to know what you find to be the problem. I am having the same issue with my 06 Cayenne. It slightly misfires about 10 to 20 times during cold start only. Once it warms up, it's perfectly fine and runs fine. My first thing to do is change the coils and spark plugs.

Edited by Peter Villalon

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Thanks for all the info!

I will post when I figure it out.

I can't imagine it's anything major for me. If I have a valve issue, It would have degraded performance, yes/no? This car rocks and all RPM except at cold idle (at which it's just rock-y, haha).

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I don't want to be a downer but I don't think anyone can tell you for sure that you don't have a more serious issue (like a valve issue or something else) before we figure out what's going on. It's good your car runs well and that this only happens on cold idle, but is still a pretty serious fundamental issue in my opinion. Even though I don't think the odds are that high in your case, anything that might have the cams out of timing isn't something I would take lightly if it were my car. This is one of the most fundamental and critical aspects of your engine. Yes, you have one of the best Porsche engines ever made....but anything is still possible.

Dump a bottle of techron in before your next full tank of gas. It's cheap and worth a shot, and good to do anyway. Never a bad idea to get your oil changed shortly after this, but I wouldn't fret too much if you're not due for an oil change just yet -- it's just good form if you can.

Get the variocam and bracket looked at closely. Make sure you are 100% sure that everything we have gone over looks ok. If you're sure about all those things I think it is in fact something more serious with the engine.... but if I had to take a shot in the dark, my money is still on an issue with the variocam. Report back once you're able to get these things we discussed looked at by a professional.

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Update to my f'd up thread... First of all, I have had no CEL since replacing the fuel cap, but I did still have some misfires, just not remotely close to enough to even issue a pending code. But, since I still had them, I know it wasn't perfect and wnted to figure it out.

Just tore the car apart. First off, solenoid brackets look perfect; no issues there.

I pulled the number 6 plug since that one fouled more than any other. It is FUGLY!

Not only is it the "wrong" plug and different than I was told was installed (Beru 5LDU versus Bosch 6LDU), but not gapped correctly, or even remotely close to it! So tight I couldn't measure it properly... But somewhere around .015" instead of the book's .06".

Any thoughts on the plug choice? I thought Porsche changed the recommended plug to the 6LDU. Clearly the main issue was the gapping, though, right?

image.jpg

post-23341-0-33430600-1387139718_thumb.j

Edited by benaslan

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The plug looked worn but its gap looks Ok and much larger than 0.015" in the photo. Are you sure you are measuring it correctly? The gap should be the min distance between the central metal cylindrical tip and each prongs.

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I was being lazy and measured it after my post: .018". Had to use a feeler gauge to get in there. That's much smaller than the .06" recommended.

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