2007 Mercury Milan PCM? Coil?

Tiny
CRAIG3777
  • MEMBER
  • 2007 MERCURY MILAN
  • 52,000 MILES
2007 Milan V6. Driving on the highway, suddenly felt as if someone had downshifted on me. Once off highway, car running rough with blinking check engine light on. Codes: P0304. P0351, P050B. So misfire in cylinder 4. Could this all be related to the coil? Do they go that fast? How do I know if the PCM needs to be replaced as well?

Thank you!
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Tuesday, September 3rd, 2013 AT 9:49 PM

3 Replies

Tiny
CARADIODOC
  • EXPERT
The ignition coils do have an unusually high failure rate, partly because they have more time for current to flow through them compared to single coils. That results in more internal heat build-up.

As far as "do they go that fast", as more and more coils of wire short together, the maximum voltage that can be produced drops until it reaches the point where the spark won't jump the spark plug's gap. That's when the misfires start. A coil can also develop a break in one of its wires. That will go from good spark to no spark in an instant.

The code 304 only indicates that cylinder is misfiring but not why. The Engine Computer knows that by the position of the crankshaft when its rotational speed slows down very slightly. It's that same momentary slowdown that causes you to feel a misfire. The Check Engine light will flash when too much raw fuel is going into the exhaust system. That can overheat and destroy the catalytic converter. You should stop the engine right away to let the converter cool down. This is a clue that the misfire is related to lack of spark, but an injector stuck open can also cause a misfire and too much fuel in the exhaust.

The easiest way to verify there's nothing more than a failed ignition coil is to switch it with one of the other ones, then see if a misfire code sets for that other cylinder. If it does, replace the coil. If you still get a cylinder 4 misfire code, swap that injector with one of the other ones. Next would be a compression test. The last thing to suspect is the computer.
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Tuesday, September 3rd, 2013 AT 11:09 PM
Tiny
CRAIG3777
  • MEMBER
The mechanic said the pcm died and melted the #4 cylinder coil. Quoted me $2600 for repairs! I called the dealership, they said the 8/80 warranty would cover the pcm and save me $1000 but have to pay for the tune up portion. The mechanic suggested I get them to cover it all! To be continued! Thank you.
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Saturday, September 7th, 2013 AT 7:13 AM
Tiny
JIMBERG98
  • MEMBER
I just went through and experienced this nightmare, but I think it's partially my fault.

My wife was pulling out of our driveway and as she shifted into drive, the car basically lost all power and started to stall. I was able to get it to run long enough to pull it back into the driveway and put a code reader on it. There was P0353 code meaning that COP C was failing. That, of course, is cyl #3 and under the intake.

I bought 3 new coils and 6 spark plugs because if I had to pull the intake, I may as well to do a tune up and replace all of the hard to get at coils. Got it all back together and then the problem moved to cyl #5 (P0355). I swapped the front coils to see if it moved. Nothing. Same thing. Swapped plug locations. Same thing. I replaced the connector for COP E. Still, the same thing. Then I just unplugged COP 5 and it moved to cyl #1 (P0351). Plugged E back in and it stayed on (P0351). Pulled the intake, swapped COP A with COP B. Still stayed as a P0351. I bought 3 more coils and replaced front 3 thinking maybe it prefers that the coils all be the same. Still, same code.

I was wondering if the Iridium spark plugs I got were the problem, so I got platinum plugs like the stock ones. As I was going to put them in, I pulled COP C and it was totally melted. Crap, at this point I knew that the computer was fried. I pulled the computer and sent it to circuitboardmedics and they turned it around in a day. In order for their warranty to be honored, I had to buy 6 new coils. Another $630.

Now here is what I think is important. New coils come with dielectric grease applied at the opening to the rubber boot. This is convenient, but is something I think that may have caused the failure. You think "wow, I can just pop these on." When you do, that grease gets all over the terminal of the plug. There's only a spring that connects with the terminal when the coil is on the plug. That will create more resistance to the plug and possibly blow out the coil. When I pulled the #1 and #3 plug, I noticed the grease all over the terminal.

When I installed the newest coils, I made sure that I smeared the grease around the inside of the rubber boot so the grease will only be contacting the insulator of the plug. I also made sure that all of my new coils had the grease in the same place. One of them actually looked like it was already used. The grease was on the spring, too. I returned this to make sure that I got a brand new coil. Considering the issue, it's a good chance that a prior customer having the same coil problems could have returned a faulty coil.

Anyway, after repairing the computer, 6 coils and spark plugs, all is good. I think the key to remember is that the dielectric grease should be spread evenly and thinly before putting it on a plug to ensure there is full contact between the plug and the spring in the coil.

This is just my guess, of course, but I think it's something that should be considered when doing the job yourself. I can see mechanics even doing this incorrectly.
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Saturday, September 27th, 2014 AT 11:22 AM

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