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Discussion Starter #1
Hello All,
I recently started to get the Check Engine Light in my Ford Taurus 2007 with the code P0300 (Random Misfire).

I used FORScan and noticed that the number of misfires increases at IDLE but when I press the throttle or when I am driving, the number of misfires does not increase.

I get misfire counts in all 6 cylinders (EWMA misfire counts for last 10 drive cycles).

"Maximum Emission Threshold Misfire Rate" is the one that is shown above the threshold - value: 1.43 % (Min: 0.00 %; Max: 1.00 %).

Can someone help me with the diagnosis?

Thank you.
 

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No uncommon to see somewhat more missfires at idle than with engine under load.

Original coil pack? If it has been replaced is the replacement a Motorcraft or BWD? Any other cheaper off brand coil packs are JUNK. Pull coil pack and inspect it carefully for any cracks, especially on the bottom. If any cracks, no matter how small, coil pack is junk.

How old are the plugs and plug wires? Correct plugs installed? Hopefully no one put Bosch plugs in the engine.

Vacuum leaks have a greater effect at idle when vacuum is high than when running. What are the LTFT values on each bank at idle and driving with the engine under load. Higher positive LTFT values at idle that drop under load = vacuum leak(s).

What fuel pressure is the PCM reporting?
 

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Discussion Starter #3
Hello Jeff,
Thanks for getting back. I replaced all 6 spark plugs, coil pack and the spark plug wires with brand new ones. I checked the firing sequence to ensure that it is correct. I am getting a P0316 Engine Misfire at Startup along with P0300.

216487


216489


Here are my data when the car at idle (800rpm and 2000rpm). My fuel trims and fuel pressure appear to be good. I'm at a loss at what to investigate next!

Thanks for your help.
 

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Make sure that the spark plug wires are connected correctly. Very easy to connect wires to the wrong spark plug. All sorts of error codes/misfires can happen. The wires on the back are easily wired wrong because you can not see the wires and it must be done by touch. Have seen it happen.
 

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Discussion Starter #5
Make sure that the spark plug wires are connected correctly. Very easy to connect wires to the wrong spark plug. All sorts of error codes/misfires can happen. The wires on the back are easily wired wrong because you can not see the wires and it must be done by touch. Have seen it happen.
Thanks a lot. I double checked the wiring just to make sure that it is wired correctly. I used the following picture that I found online (big numbers = cylinders; small numbers = coils):
216490

I'll check again in the morning just to be 200% sure that I did not mess up.

Thanks for the quick response.
 

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Have you actually reset the codes because it is showing no actual misfires at current time and two trips since last misfire. Not expert on Forscan but have used it a couple of times. I thought random misfire is when the car can't determine which cylinders are misfiring. I would look for a vacuum leak that is in the snorkel area and possibly the runner control valve on the backside of the intake passenger side. Your short term fuel trims I believe are high unless I am looking at wrong parameters. Can't remember what I look at for that info on the program, you have so many listed.
 
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