Diagnosing and Resolving Cylinder Misfire DTCs

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Mar 16, 2009
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I purchased a 2011 Fusion SE with 109K miles a couple of months ago for my daughter to drive. There have been two occasions when the check engine light came on, both while she was driving on the highway. She said there was no "hiccup", loss of power, or anything otherwise noticeable and that the car continued to drive fine in both instances. Using FORScan and Car Scanner ELM OBD2 I have been able to see the errors and clear them.

The first time they were:
P0300 - Random Misfire Detected
P0304 - Cylinder 4 Misfire Detected

The second time they were:
P0300 - Random Misfire Detected
P0301 - Cylinder 1 Misfire Detected

There was about 5 weeks and 1,500 miles of city driving in between during which everything was fine.

My initial thoughts are the spark plugs and/or ignition coils. Both are relatively easy and inexpensive to replace. But before I start chasing the problem and replacing parts, I wanted to see what folks with more experience would recommend.
 
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your mileage is about the time to replace the spark plugs, as most OE iridium intervals are around 100k :unsure:

If you keep running with worn spark plugs, you could wear out the coils faster than they otherwise would, but there is no need to replace them now unless coil failure is common on the Fusion.

It's a different cylinder each time, and there were no other symptoms than the codes. In a serious misfire, the car would shake and the CEL would blink.
 
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I agree it is due for new plugs, and I'd change the wires while you're at it.

Since you have Forscan and the dongle, if new plugs doesn't resolve it, look at the live data, long term fuel trim. If high you might have low fuel pressure or a vac leak.
 
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Not wanting to throw parts at the wife's 4Runner, I chased a random P0300 and not so random P0306 for several months recently. Turned out to be a bad injector in number 6 cylinder.
The 4Runner ran fine most of the time. If you started it up it ran fine. Stop at a store or whatever for a little while then start it up it would throw the code. The problem I had diagnosing this thing is it would run fine before getting home. Something was getting heat soaked and then cooling while driving.
I swapped the spark plug and coil pack in #6 and read live data with no help.
I figured heat soak while sitting at the store parking lot (coil pack). It turned out to be the injector solenoid was getting heat soaked and after a short drive it cooled off.
 
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With no known maintenance history I would start with new plugs and wires. Not so sure about the wires but the plugs are due. Also, don't forget the fuel filter. It should be long overdue for a change and would be my first choice along with plugs. After that it would likely be coils or injectors.
Unfortunately there can be other things that could cause this. MAF or MAP sensor or EVAP system problem to name a few. Even a bad gas cap gasket.
 
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I would diagnose the misfire instead of assuming that maintenance will fix it.

At the very least, even if you have minimal tools, you can move the position of the plugs and coil packs to see if the misfire follows.
 

barlowc

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Thank you for all the input! Since the previous owner did not have a detailed service record, I don't know if the spark plugs have ever been replaced. I ordered a set of the OE Motorcraft ones and am going to start there. It's an inexpensive and simple thing to rule out.
 
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I agree it is due for new plugs, and I'd change the wires while you're at it.

Since you have Forscan and the dongle, if new plugs doesn't resolve it, look at the live data, long term fuel trim. If high you might have low fuel pressure or a vac leak.
It is a COP system.

You will likely get lean codes first with high fuel trims.
 
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Thank you for all the input! Since the previous owner did not have a detailed service record, I don't know if the spark plugs have ever been replaced. I ordered a set of the OE Motorcraft ones and am going to start there. It's an inexpensive and simple thing to rule out.
Replace the coil boots too. I've seen too many cases where people will do plugs, but not boots, then later they'll have a misfire due to a bad boot


Also inspect the coils - look for hairline cracks in the potting on top
 
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If it's the 2.5 I4, I went through similar with my late Milan (almost identical milage too)
If it hasn't had the updated throttle body, that could be acting out
Same for the purge valve
Mine would give a flashing misfire after washing the engine bay, but only hot on the highway with the A/C on, slight grade
All other times it would run on all 4 cylinders smoothly
I hate to throw parts at things, but knowing that platforms common problems
Updated throttle body + purge valve
New Motorcraft plugs and coils
All of that conspired to make that engine start/run/pull like a dream
Shame it got totalled 🙁
Check with FORScan & Mode 6 data while misting near/around the coils with water
 

wtd

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Does the engine in this car have the plugs and coil boots down through the valve cover? If so, a leaking valve cover gasket can put oil down inside the plug wells and cause a misfire. We had that situation on a 2008 Ford Focus my fiancé bought for her son a couple of years ago. Two of the plug wells were filled to the top with oil. We did replace the plugs and coil boots when replacing the valve cover gasket.
 
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I’d do what atikovi suggested - but if you have a ELM327 Bluetooth OBD-II dongle(I recommend Carista or BlueDriver), FORScan can also access the Power Balance chart Fords have. Any Chinese(Autel/OttoFix, Launch/ThinkCar) with bidirectional control/live data and Ford software loaded, Snap-On or pro-level OTC scanner should also be able to access Power Balance on Fords. That way, you can see what’s going on with the engine in real-time.
 
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