P0303 Cylinder 3 Misfire
#1
P0303 Cylinder 3 Misfire
Hello. I have a 2008 Mini Cooper base, N12 engine. I keep getting the Check Emgine Light with code P0303 Cylinder 3 Misfire. I had it at the shop where the mechanic:
1. Cleaned the Mass Air Flow sensor
2. Replaced Valve Cover gasket
3. Replaced Spark Plugs
4. Changed Serpentine belt
5. Oil and filter change
6. Compression Check. All cylinders were between 150-160.
7. Swapped Coil Packs
He test drove it after completing the work and said the code was reset and the car was running great. I then drove it home and it ran awesome. However, when I pulled into my driveway, the idle was rough again and then the Check Engine Light came back with the Cose P0303!!!!!!!!
I tried the Seafoam through the intake vacuum line and some in the gas tank, but had no luck here.
I called the mechanic and he recommended swapping Fuel Injectors. I reset the Codes and then swapped injector 3 to 4.......but the Check Engine light with P0303 came back!!!!!
It seems to me that when cold, the engine idles great.....but after the engine has warmed up, the idle becomes rough. The car drives great once moving through all 6 gears. Both the mechanic and I are out of ideas. Please help. Any ideas or recommendations are welcome. Thank you.
1. Cleaned the Mass Air Flow sensor
2. Replaced Valve Cover gasket
3. Replaced Spark Plugs
4. Changed Serpentine belt
5. Oil and filter change
6. Compression Check. All cylinders were between 150-160.
7. Swapped Coil Packs
He test drove it after completing the work and said the code was reset and the car was running great. I then drove it home and it ran awesome. However, when I pulled into my driveway, the idle was rough again and then the Check Engine Light came back with the Cose P0303!!!!!!!!
I tried the Seafoam through the intake vacuum line and some in the gas tank, but had no luck here.
I called the mechanic and he recommended swapping Fuel Injectors. I reset the Codes and then swapped injector 3 to 4.......but the Check Engine light with P0303 came back!!!!!
It seems to me that when cold, the engine idles great.....but after the engine has warmed up, the idle becomes rough. The car drives great once moving through all 6 gears. Both the mechanic and I are out of ideas. Please help. Any ideas or recommendations are welcome. Thank you.
#3
#4
If the cylinder leak down test comes back good then it could be a timing chain. The vanos units can compensate for a good amount of stretch. And the N12s don't get that rattle when the chain stretches. If the chain stretches too much the intake valve timing goes out just enough to cause the valve to hang open and misfire.
#5
Thanks for the advice and info. The car is in great shape but it does have 140,000. I got most of the service records from the previous owner, who is a good friend. No record of the timing chain being replaced.
I will call the mechanic and pass the info on to him:
1. Leak down check
2. Fuel rail pressure
3. Timing chain
4. Camshaft Position Sensor
Good info here!
Thanks again
I will call the mechanic and pass the info on to him:
1. Leak down check
2. Fuel rail pressure
3. Timing chain
4. Camshaft Position Sensor
Good info here!
Thanks again
Last edited by EMKFLYER; 06-13-2014 at 04:22 AM.
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#9
Leak down test was competed hot and cold. All 4 cylinders were good at about 78/80. Timing components all look new.
The car started running rough again and now got code P115c and 2B56.
Smoke tested intake no leaks. Cleaned maf. Cleared codes runs smooth again. MAF has been replaced in 2012. Out of ideas.
Please help. Ed
The car started running rough again and now got code P115c and 2B56.
Smoke tested intake no leaks. Cleaned maf. Cleared codes runs smooth again. MAF has been replaced in 2012. Out of ideas.
Please help. Ed
Last edited by EMKFLYER; 06-19-2014 at 02:20 PM.
#12
78-80% on the leak down test tells me that you have about 20% leak down. So most likely you have valves hanging open. The timing components looking new only tells me that the oil level was kept up and oil changes were done on time. I would check the engine timing and measure the chain. N12 new chain is 62mm. If it stretched more than 5mm then it needs replacement. It could also have a collapsed tensioner for the timing chain which would explain the hot idle issue. When the oil is cold and thick it keeps the tensioner out and when it warms up and thins out the tensioner doesn't keep the chain tight. Also check if the engine is in time I have seen them lose time due to stretch by 1 tooth and cause this.
#13
No you need to actually see the fuel rail pressure with the engine running, forget codes as they can only tell you so much. You have no clue what your fuel rail pressure is do you? You need to eliminate this as a possible cause. They haven't done much in the way of helping you, just more questions than answers.
#14
They shop is closed now, but I left a message about checking the Fuel Rail pressure and the timing chain again.
To my knowledge the timing chain has never been replaced, but Mini of Pensacola says the tensioner was replaced at 80,000 (I'm currently at 140,000 miles)
Any idea how either of these issues could cause a P115c code?
Thank you all again for the time trouble shooting this a Mini.
To my knowledge the timing chain has never been replaced, but Mini of Pensacola says the tensioner was replaced at 80,000 (I'm currently at 140,000 miles)
Any idea how either of these issues could cause a P115c code?
Thank you all again for the time trouble shooting this a Mini.
#15
Just another thought............
The previous owner has had this same issue since last year. The car has essentially been parked for over 8 months due to their frustrations with the car. Any chance the Ethynol or bad gas is causing any of these issues after sitting so long?
I got a really good deal on this car ($2000 US Dollars) that is in almost perfect shape other than the above issues.
The previous owner has had this same issue since last year. The car has essentially been parked for over 8 months due to their frustrations with the car. Any chance the Ethynol or bad gas is causing any of these issues after sitting so long?
I got a really good deal on this car ($2000 US Dollars) that is in almost perfect shape other than the above issues.
#16
I agree about forgetting the codes. The rail pressure should be checked but I think that if it was a pressure issue that cylinder 4 would misfire as well since it gets fuel before cylinder 3 or if it was starving for fuel that cylinders 1 and 2 would set misfires since they are after 3 in the rail. If the chain was done at 80k and you have about 140k on it-its coming due to need a replacement soon. N12 chains have no recall or updated parts so that could just be the lifespan of the chain in your engine. The 62mm measurement as new I took myself after the 11th chain I did on a N12 with misfire faults that ended up being the chain. I have not ever found a published spec anywhere. N14 chains start at 64mm and the recall says if its over 68 or 69mm to replace it. That's just 4-5mm stretch.
#18
The mechanic just texted me the following:
One other thing I thought of, when looking at the mass airflow data on the scan tool........."When looking at the mass airflow data on the scan tool with the engine shut off it read: after the engine was running rough, still showing 2.5 kilograms an hour (confused why we would still get a 2.5KG reading with engine shut off). After we did all the work and the engine started running smooth it read 0 kg/h after the engine was shut down.
Any thoughts on the air flow here?
Last edited by EMKFLYER; 06-20-2014 at 10:44 AM.
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