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P0351 Help! 2008 Mercury Sable with misfire issues

Old 06-18-2018, 04:01 PM
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Default P0351 Help! 2008 Mercury Sable with misfire issues

Hi everyone,
My wifeís car decide to get an attitude last week. It was idling rough and having performance issues with massive misfires once you get up to over 40 mph. The Sable gave the codes P0351,352, and 354. At this point, the car was not ďdriveableĒ. She limped home at speeds up to 25 mph no problem.

To start with, I replaced the plugs and ignition coils, looked around for obvious vacuum leaks and visually inspected the wiring. Once I got the Sable put back together and on the road there was a MASSIVE improvement in how the vehicle ran. I can tell only from knowing how the vehicle drove before, that it is having some misfires when she is idling. Barely noticeable; however, she starts to act up and have misfires at speeds around 60 mph. For some weird reason, it isnít as noticeable if OD is off. Even tho she is having misfires, itís now very minor and she is driveable.

Heres where I am stuck st and need your advice. Before, the Sable only turned on the engine light with codes when you started driving her. Turning her over was fine. Also, she was not driveable at speeds above 25 mph. Now, the engine light turns on immediately without actually turn the engine over, simply putting the key and giving her electricity turns the engine light on. However, now there is only the code P0351. She is driveable at all speeds, but there is some very minor performance / misfires. Even weirder, is if i clear out the engine light / P0351 with my ODB tool - the engine light will stay off! She drives consistently without an engine light but something minor is causing barely noticeable misfires.

As it requires electricity, not the engine running, the code is the same, and the code doesnít return if itís been cleared - I am inclined to say the PCM got fried.

Opinions, feedback, emotional outbursts? Before i replace the PCM, has anyone had this issue? All repair manuals point to it being the PCM, but it could be a camshaft or crankshaft sensor. I donít have access to the diagnostic software / hardware and mechanics in my area are thieves and charge a ridiculous amount here. I live in a town where the cost of living is ridiculous and thereís a higher percentage of people living in the top income bracket ssssoooo.


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