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


benaslan

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I have had these codes on misfires forever. I cannot get them to go away.

I have had it in the shop and they replaced all coils and plugs.

I replaced the MAF last week as a long shot just for the hell of it.

Code resets itself after 7 clean starts. (Then will come back at some point).

It is ALWAYS AT COLD FIRST START IDLE OF 1,120 RPM (first thing in the morning and no other time).

Please help!

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I'm using an Innova scanner, model 3100.

This is the data that is saved by this scanner:

Parameter Description Results DTC for which Freeze Frame was Stored P0300 Fuel System 1 Status Closed Loop Fuel System 2 Status Closed Loop Calculated LOAD Value 5.49 % Engine Coolant Temp 77.00 °F Short Term Fuel Trim - Bank 1 -3.91 % Long Term Fuel Trim - Bank 1 1.56 % Short Term Fuel Trim - Bank 2 -10.16 % Long Term Fuel Trim - Bank 2 0.00 % Intake Manifold Absolute Pressure 75.51 inHg Engine RPM 1,120.00 rpm Vehicle Speed Sensor 0.00 mph Monitor Name Monitor Icon Status MIL (Check Engine Light) Display-icon-CheckEngine.gifON Misfire Monitoring Display-icon-2-M-small.gifComplete Fuel System Monitoring Display-icon-2-F-small.gifComplete Comprehensive Component Monitoring Display-icon-2-CC-small.gifComplete Catalyst Monitoring Display-icon-2-C-small.gifNot Supported Heated Catalyst Monitoring Display-icon-2-HC-small.gifNot Supported Evaporative System Monitoring Display-icon-2-EV-small.gifNot complete NMHC Monitoring Display-icon-2-NM-small.gifNot Supported NOxAdsorber Monitoring Display-icon-2-N-small.gifNot Supported Secondary Air System Monitoring Display-icon-2-2A-small.gifComplete Oxygen Sensor Monitoring Display-icon-2-O-small.gifComplete Oxygen Sensor Heater Monitoring Display-icon-2-OH-small.gifComplete EGR System Monitoring Display-icon-2-E-small.gifNot Supported Boost Pressure System Monitoring Display-icon-2-BP-small.gifNot Supported Exhaust Gas Sensor Monitoring Display-icon-2-EG-small.gifNot Supported PM Filter Monitoring Display-icon-2-P-small.gifNot Supported

And no, I'm not sure of anything. I have thought about that being the issue, but read that it is usually indicated by misfires on all of the same bank, which I don't get. I suppose anything is possible. Is there an easy way to check?

Thanks!

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+1 to what Loren said. You definitely don't want to use anything else other than Durametric or PST2/PIWIS on these cars. You need to baseline what's going on by doing a scan with a tool which will give you reliable results. You can also check the camshaft attributes from these tools.

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"Intake Manifold Absolute Pressure 75.51 inHg". That is 2.6 bar absolute pressure. The engine is on boost when idling? Doesn't seem to make sense...

Are you saying that may be the problem? Wouldn't a misfire create a whole lot of pressure in the engine? This is a snapshot of when the misfire occurs.

My durametric will be here tomorrow. Any tips for use in diagnosing this would be appreciated. I've never used one.

Thanks again!

Edited by benaslan
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"Intake Manifold Absolute Pressure 75.51 inHg". That is 2.6 bar absolute pressure. The engine is on boost when idling? Doesn't seem to make sense...

Are you saying that may be the problem? Wouldn't a misfire create a whole lot of pressure in the engine? This is a snapshot of when the misfire occurs.

My durametric will be here tomorrow. Any tips for use in diagnosing this would be appreciated. I've never used one.

Thanks again!

I don't think misfire will create pressure in the intake (you may be thinking about backfiring). I don't know enough about 996 TT but I would not expect the engine to be on boost at idling in general. Maybe the pressure sensor is sending wrong measurements, or the engine is really on boost, or the scanner is wrong.

I hope someone who knows could chime in with typical intake pressure value during cold idling for your car.

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I'm not a gambler but I bet it's the scanner and that's not correct. You often see things like this when using scanners that aren't Porsche specific. They can miss codes or throw phantom codes. You will know tomorrow once your Durametric arrives. Let us know how it goes.

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Okay, so my Durametric finally came 4 days late (thanks UPS for my "2 day" air that took the scenic route).

Only codes it shows are the misfire codes. Same cylinders... (in the Engine Faults area)

I also see: "fuel tank ventilation - Fail"

Is there something else I should be looking at? Do I need to have it connected while it happens to log it?

Thanks,

Ben

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This is good. So now you at least know what the real problems are -- much easier to troubleshoot this way. One other thing is it's always ideal to post the actual error code (and not just the description). Based on what you are showing, I would address the issue with the fuel tank ventilation system. Usual culprit is the gas cap or seal so I would check that to start.

If you do want to monitor the car in realtime as you mentioned, this is possible using the Durametric. Yes, you will need to have it connected to the car while it's running to capture the logs in Durametric. There are a TON of variables you can monitor in the DME.

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Ok, I see. That is one of the emissions checks then. Just FYI as we are getting close to the end of the year, you won't be able to pass an emissions test until you get that fixed.

The cap is the usual suspect and cheapest place to start. Before you just replace it for no reason though I would specifically inspect it and the seal. Make sure it's creating an air-tight seal and there isn't a vacuum leak.

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A lot of these "readiness states" are not set instantaneously and are rather set as the DME takes measurements over a period of time. It's possible this issue has manifested itself since you had the test done, but this should have shown up if it was the kind of test where they simply plug in their reader through he OBD2 port and you did have this issue at the time. As a matter of fact, most states now don't even actually test these "states" directly -- they simply query these "ready states" from your DME and ask if everything is ok. If you're car says "PASS" to all of them, they give you a pass and you go on your way for the next year or two until the next test.

If this is the gas cap, which it often can be, this is the cheap-to-replace low-hanging fruit so to speak. You need to be sure you're getting a nice tight seal. I would address this first, as it could be the cause of your misfires..... have you looked at your fuel trims? A vacuum leak could cause your fuel trims to go out of spec and therefore cause misfire(s). You should be able to monitor the fuel trims in the Durametric in realtime, and I would test as the RPM increases. If your fuel trim keeps getting leaner as RPM increases, this indicates a fuel delivery issue -- aka unmetered air entering into the system from that leak. To this point, you may be able to hear the air leak at the gas cap as you rev the engine a little.

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Update:

It may take me awhile to make sense of this, and not sure I selected the correct variable to look at, but hopefully just too many. If I am understanding correctly, there is more often a misfire than I thought, it just does not always make the CEL go on. Only ones that have made it go on are at cold high idle previously, unless my code reader was giving incorrect info, which is possible.

I think this shows I have other misfires. My light is off currently since I reset it last night. This log is from this morning, but I had a hard time setting up logging for the first time and car was partially warmed up before I got it going...

Any input on this spreadsheet of data? What should I be looking for, or what other values should I add into the log?

LOG FILE HERE: https://drive.google.com/file/d/0B0SIEMPr2EXYSDlMUFdoRXRrcFk/edit?usp=sharing

Let me know if that link doesn't work.

Thanks!!!

***I just did a search and it seems that the CEL is activated if a certain number of misfires in the same cylinder over a short period of time. So maybe the ones shown are not important and I really need to capture the ones on cold high idle?

Edited by benaslan
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Link does not work for me. I don't have it in front of me but it should be pretty easy to find if you look through all the variables. You can also simply call Durametric and ask them where they are in the software interface. They are friendly and generally answer the phone with a person without going through a lot of prompts. I'm sure they would be happy to answer a question like this for one of their new users.

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Yes, the CEL is only triggered by the DME similar to what I described above when a certain threshold of criteria is met (eg. so many misfires within a certain period of time). However, that said you really should not be getting misfires, so I would start by addressing the issue above and then starting to think about things like when the last time was that you changed your coil packs and plugs.... and making sure you have good, fresh fuel with no moisture. Like I said above though, if you have a vacuum leak in the fuel tank, it can cause unmetered air to enter and cause you to run too lean, which could potentially result in a misfire.

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Agree with Silver about coils and plugs. Obviously cylinder#4 is having misfire. The other thing is your cam deviations are varying a lot as the engine warms up. Not sure if hat's the thing with turbo cars. Mine is N/A and the cam deviations are rock solid regardless of revs. The values can change from start to start a little bit (say +/-0.1) but once eninge is running, the values stay the same regardless or revs.

I think if it's consistently only cylinder #4, you may need a compression and leak down test to verify its health.

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Just replaced the fuel cap and that took care of the fuel ventilation issue. No more fuel vent issue. Not sure if my problem is fixed or not, we'll see. As for the main issue if it comes back:

Plugs and coils were replaced 6 months or so ago to address this problem. It did nothing, no change. I feel it running stronger since then, but no fewer misfires, nor a difference in which cylinders (primarily 3,5,6 are the ones that give codes). Don't think I've every gotten a code from 4.

Problem has been intermittent for 3 years with zero drive-ability issues and zero other codes. Certainly not a fuel issue as I only use premium gas and 3 years running...

I do have a code showing but no CEL. It's a random misfire and cyl 6.

Here is a new log from my trip to get the gas cap if anyone is bored and wants another look. I got onto it plenty in this one. Feels great, no hesitation under full load.

https://drive.google.com/file/d/0B0SIEMPr2EXYVmFlQ3J0ZmlRTnc/edit?usp=sharing

No misfires on 4. Could the tappet valve brackets be causing the cam variation, or is that not enough variation to indicate an issue? Loren, any idea?

Thanks again!

I will clear the pending codes and see what happens later tonight or tomorrow morning.

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Ok, so you're still getting misfires. And how do the fuel trims look against spec?

It's always good to give background on recent service, such as you said you just had the plugs and coil packs done. You use premium gas, and that's fine, but I was referring to moisture and just making sure the fuel is fresh. For folks that keep the car in a more humid climate this can be an issue, especially if the car isn't driven every day.

Even if the cap fixed your gas tank issue, you still need to make sure the fuel trims look ok. If you have done all this and are comfortable with what you are seeing then, like Ahsai said, it may be time for a leak down compression test. Anything is possible, however, this wouldn't be my first guess as your engine is widely known as one of the best engines Porsche ever made. Things happen, but if maintained properly these engines are not often as prone to fundamental failures.

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