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Code 306

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32wildbilly
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Code 306

Post by 32wildbilly » Tue Sep 11, 2018 2:26 pm

Yesterday started the car, backed it out, patiently waited for air injector to cycle off and idle to drop. Drove out of driveway and out to street(live on a small circle). While driving to street noticed pronounced roughness in engine. Turned right on street in a reasonable manner, got the dreaded flashing CEL with warning "drive to service center". Backed off throttle and began looking for driveway to turn around in. At this point the engine calmed down and the CEL went out as well as the CPU warning. Drove car to destination and returned no problem. Checked the code on return and it was 306 #6 cylinder misfire. This happened this spring after an extended rainy period and never since. I know it's probably a cracked coil or Beelzebub in my engine, but my question is: When this happens then everything straightens out, lights/warning goes out and engine runs fine. Other than I know I need new coils which is planned for this winter in addition to plugs and injectors, should I be concerned. The code reader gave the code and said "pending". Is this just the code reader saying I found this code what do you want me to do with it or what? 2005 C4S 54,500 miles.

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sweet victory
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Re: Code 306

Post by sweet victory » Wed Sep 12, 2018 7:21 am

I doubt there was anything damaged from a high/low fuel trim. Your have a problem with fuel delivery, vacuum leak, or spark. Sounds like you already know what your problem is. The reason it ran rough after warming up is because during the warm up process, your ecm does not respond to 02 sensor data. After the car warms up, it becomes a closed loop, and the 02 sensors will take over and the ecm adjusts the short term fuel trims as necessary. I wouldn't be worried about it, but I also wouldn't continue to drive the car.
2001 996 C2 Aero

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Black-Out
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Re: Code 306

Post by Black-Out » Thu Sep 13, 2018 8:06 pm

sweet victory wrote:
Wed Sep 12, 2018 7:21 am
I doubt there was anything damaged from a high/low fuel trim. Your have a problem with fuel delivery, vacuum leak, or spark. Sounds like you already know what your problem is. The reason it ran rough after warming up is because during the warm up process, your ecm does not respond to 02 sensor data. After the car warms up, it becomes a closed loop, and the 02 sensors will take over and the ecm adjusts the short term fuel trims as necessary. I wouldn't be worried about it, but I also wouldn't continue to drive the car.

I second this....If you continue to drive with a misfire it can permanently damage the expensive catalyst on you 911 and trust me when I tell you it doesn't have to be driven far before the damage is done........ ask me how I know.... -_-
William-
Current Ridez:
87' Dodge Conquest TSi
88' BMW 635CSi
89' Merkur XR4Ti
90' Mitsubishi 3000GT VR-4
95' BMW M3
99' BMW 328i Sedan
00' BMW 528i Sedan
00' Pontiac Fire Hawk Trans-Am
02' Porsche 911 Carrera
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32wildbilly
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Re: Code 306

Post by 32wildbilly » Fri Sep 14, 2018 5:38 am

Black-Out wrote:
Thu Sep 13, 2018 8:06 pm
sweet victory wrote:
Wed Sep 12, 2018 7:21 am
I doubt there was anything damaged from a high/low fuel trim. Your have a problem with fuel delivery, vacuum leak, or spark. Sounds like you already know what your problem is. The reason it ran rough after warming up is because during the warm up process, your ecm does not respond to 02 sensor data. After the car warms up, it becomes a closed loop, and the 02 sensors will take over and the ecm adjusts the short term fuel trims as necessary. I wouldn't be worried about it, but I also wouldn't continue to drive the car.

I second this....If you continue to drive with a misfire it can permanently damage the expensive catalyst on you 911 and trust me when I tell you it doesn't have to be driven far before the damage is done........ ask me how I know.... -_-
I guess this is my question: Due to the fact that the CEL light, the cpu warning went out and the engine went back to normal running is there a problem currently? Yes I know there are the above mentioned items to change, but it does not currently seem to be misfiring...Should I reset the stored code and see if it reoccurs before winter maintenance time?

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OceanBlue2000
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Re: Code 306

Post by OceanBlue2000 » Fri Sep 14, 2018 6:26 am

My understanding of a pending code (from looking at cars to buy with pending codes) is that pending means, "the car is about to trip this code, it just hasn't had X happen enough times for it to be tripped." Meaning, if your question is whether the car still has an issue, a pending code is not great news.
Mike
Strange things I have in head, that will to hand.
2000 Ocean Blue 996 Carrera 2
1982 928 (sold)

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sweet victory
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Re: Code 306

Post by sweet victory » Fri Sep 14, 2018 6:57 am

32wildbilly wrote:
Fri Sep 14, 2018 5:38 am
Black-Out wrote:
Thu Sep 13, 2018 8:06 pm



I second this....If you continue to drive with a misfire it can permanently damage the expensive catalyst on you 911 and trust me when I tell you it doesn't have to be driven far before the damage is done........ ask me how I know.... -_-
I guess this is my question: Due to the fact that the CEL light, the cpu warning went out and the engine went back to normal running is there a problem currently? Yes I know there are the above mentioned items to change, but it does not currently seem to be misfiring...Should I reset the stored code and see if it reoccurs before winter maintenance time?
Sounds like an intermittent problem for now. Hard to say for sure with the limited info.

I would not clear any codes until after you've at least changed your spark plugs/coils.
2001 996 C2 Aero

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Re: Code 306

Post by 808Bill » Fri Sep 14, 2018 1:06 pm

Why chance it?

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Black-Out
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Re: Code 306

Post by Black-Out » Fri Sep 14, 2018 6:17 pm

32wildbilly wrote:
Fri Sep 14, 2018 5:38 am
Black-Out wrote:
Thu Sep 13, 2018 8:06 pm



I second this....If you continue to drive with a misfire it can permanently damage the expensive catalyst on you 911 and trust me when I tell you it doesn't have to be driven far before the damage is done........ ask me how I know.... -_-
I guess this is my question: Due to the fact that the CEL light, the cpu warning went out and the engine went back to normal running is there a problem currently? Yes I know there are the above mentioned items to change, but it does not currently seem to be misfiring...Should I reset the stored code and see if it reoccurs before winter maintenance time?


If your 911 is currently misfiring you should get a flashing check engine light and the rough running will be evident. The pending code is when the ECM recognizes the condition has happened in the drive cycle before, is not occurring during the current drive cycle, but if it sees misfiring again it will trip the code during the fault occurrence. The problem with all that is when the cylinder goes dead, The ECM never stops firing the fuel injector on the effected cylinder. That unburned fuel vapor then gets delivered directly to the catalyst and then gets ignited within the cat due to high temperatures needed to convert small amounts of hydrocarbons and NOX to H20. When the significantly larger amount of Hydrocarbon (unburned fuel) hits the already hot cat, the temperature spikes dramatically (they can literally get red hot to a point that you can see it in broad daylight).

Now on a lesser catalyst, (specifically one made out of ceramic) the core will melt over if the spike continues and the fueling isn't cut off on the problematic cylinder, Porsche started using all metal core catalyst back in production date 6/1999 for the 2000 model year. instead of the catalyst melting shut and clogging the engine, The cat will get super heated and when it does the excessive heat strips the rhodium off the core rendering the cats conversion ability severely handicapped. The computer then picks up on the compromised performance because the secondary O/2 sensor signal begins to mirror the voltage that the primary Lambda Sensor is producing putting the reading out of range and then tripping you a subsequent code for PO420 Catalyst inefficiency and quite possibly causing you a PO491 and PO492 secondary air injection code, because of the faulty secondary O/2 sensor readings. This is because Porsche checks the secondary air injection function, by looking at the secondary O/2 sensor voltages...... Now if you want to, you can clear the code, but I highly recommend you copy all the stored data as well as the codes, BEFORE you erase it, giving your tech a fighting chance at finding the issue and fixing it. It sounds like you know for sure it'll be cracked coil pack casings causing the misfire (as it usually is when they get this age) but just in case it isn't, you'll need to give as much information to the tech as possible in order for him to have a full picture of whats going on... Just my two cents.....
William-
Current Ridez:
87' Dodge Conquest TSi
88' BMW 635CSi
89' Merkur XR4Ti
90' Mitsubishi 3000GT VR-4
95' BMW M3
99' BMW 328i Sedan
00' BMW 528i Sedan
00' Pontiac Fire Hawk Trans-Am
02' Porsche 911 Carrera
08' BMW 335i Coupe
10' Mercedes Benz E350 4-Matic AMG Sport

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32wildbilly
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Re: Code 306

Post by 32wildbilly » Fri Sep 14, 2018 6:58 pm

Black-Out wrote:
Fri Sep 14, 2018 6:17 pm
32wildbilly wrote:
Fri Sep 14, 2018 5:38 am


I guess this is my question: Due to the fact that the CEL light, the cpu warning went out and the engine went back to normal running is there a problem currently? Yes I know there are the above mentioned items to change, but it does not currently seem to be misfiring...Should I reset the stored code and see if it reoccurs before winter maintenance time?


If your 911 is currently misfiring you should get a flashing check engine light and the rough running will be evident. The pending code is when the ECM recognizes the condition has happened in the drive cycle before, is not occurring during the current drive cycle, but if it sees misfiring again it will trip the code during the fault occurrence. The problem with all that is when the cylinder goes dead, The ECM never stops firing the fuel injector on the effected cylinder. That unburned fuel vapor then gets delivered directly to the catalyst and then gets ignited within the cat due to high temperatures needed to convert small amounts of hydrocarbons and NOX to H20. When the significantly larger amount of Hydrocarbon (unburned fuel) hits the already hot cat, the temperature spikes dramatically (they can literally get red hot to a point that you can see it in broad daylight).

Now on a lesser catalyst, (specifically one made out of ceramic) the core will melt over if the spike continues and the fueling isn't cut off on the problematic cylinder, Porsche started using all metal core catalyst back in production date 6/1999 for the 2000 model year. instead of the catalyst melting shut and clogging the engine, The cat will get super heated and when it does the excessive heat strips the rhodium off the core rendering the cats conversion ability severely handicapped. The computer then picks up on the compromised performance because the secondary O/2 sensor signal begins to mirror the voltage that the primary Lambda Sensor is producing putting the reading out of range and then tripping you a subsequent code for PO420 Catalyst inefficiency and quite possibly causing you a PO491 and PO492 secondary air injection code, because of the faulty secondary O/2 sensor readings. This is because Porsche checks the secondary air injection function, by looking at the secondary O/2 sensor voltages...... Now if you want to, you can clear the code, but I highly recommend you copy all the stored data as well as the codes, BEFORE you erase it, giving your tech a fighting chance at finding the issue and fixing it. It sounds like you know for sure it'll be cracked coil pack casings causing the misfire (as it usually is when they get this age) but just in case it isn't, you'll need to give as much information to the tech as possible in order for him to have a full picture of whats going on... Just my two cents.....
Thanks! Very informative. I will figure out how to down load the info and leave the code behind. Car ran clean and strong today with no vibration, lights or warnings.

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Re: Code 306

Post by Black-Out » Wed Sep 19, 2018 7:04 pm

Any time man!
William-
Current Ridez:
87' Dodge Conquest TSi
88' BMW 635CSi
89' Merkur XR4Ti
90' Mitsubishi 3000GT VR-4
95' BMW M3
99' BMW 328i Sedan
00' BMW 528i Sedan
00' Pontiac Fire Hawk Trans-Am
02' Porsche 911 Carrera
08' BMW 335i Coupe
10' Mercedes Benz E350 4-Matic AMG Sport

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