Misfire cylinder 4, it can get pretty severe. Violently shaking the van. on 2005 Mercury Monterey

We change the oil and it goes away for a few months. We change the synthetic oil about every 2 months whenever the problem comes back. How do we fix this?
Check engine light flashes when it gets bad. Check engine code is only misfire in cylinder 4.

Asked by for the 2005 Mercury Monterey
Repair misfire on cylinder number four! Possible causes are: coil pack, spark plug, spark plug wire, fuel injector, vaccum leak or low compression.
2 more answers , 2 more comments
Has the #4 spark plug been inspected for oil fouling? Possible sticking rings. Maybe , next oil change , try adding a quart of Marvel Mystery Oil , instead of a quart of regular oil & see if that helps.
Hi, there is most likely only a few reasons why misfire is occurring, spark plugs,wires,coil,injector or Bad valve have you done anything other than change oil?
We haven't tried anything else. Chang the oil will relieve the problem but it doesn't fix it, out comes back in a few months. I'm curious how/why changing the oil would cause/prevent a misfire.
That is very odd, we had vehicles in the past with massive amounts of sludge and by flushing oil it would help with oil pressure but this doesn't sound remotely similar, sound like possibly a coincedence? If you can't figure it out feel free to bring it by our shop we will do our best to get your car back running good, we are located in Federal Way. Thanks and good luck
Qualified Local Mercury Shops
Qualified Mercury Shops For This Repair
29805 Pacific Highway S
Federal Way
(206) 557-6618