Hey all,

I’ve had an intermittent misfire in cylinder 6 for some time. Only ever happens at idle, truck smooths right out when I accelerate. Hasn’t happened for over 6 months, and now two days in a row. Haven’t done any work to the truck apart from an oil and filter change two weeks ago.

edit: ‘08 3.0L Sport

Have read other threads with this issue and it seems many throw parts at it to no avail. I know I need to do a compression test from looking at other threads, and RonD’s helpful replies. Planning on it. Sidenote: if compression is off on that cylinder, what should be done to fix it?

Anyways; before I bite the bullet and get a compression testing kit, have a few theories. It appears my valve cover has a small oil leak above the cylinder 6 spark plug. Could this cause a random misfire? Perhaps through oil fouling the plug? I did new plugs and wires about a year ago in response to the first misfire. I’ve also read it could be coil pack. I’ve attached a photo of the leak.

Just wondering what would cause it to be seemingly random. I would think if it was a bad injector (I run Seafoam through the tank every couple months) it would be constant. Likewise, if it’s a bad IAC, would this cause a misfire on a single cylinder / be random?



Would changing the PCV valve stop the leak and or help this issue? I’ve read it can cause valve cover leaks. I won’t be able to take the cover off until the summertime when I can get to my uncles garage as he has a better setup and more experience than my condo parking lot, haha.

Thanks for reading and any tips appreciated.

 

Some things to think about maintenance wise. I get the "don't just throw parts at it" hoping it will fix it. However, you didn't share mileage or service history. These points are important as parts have a service life and the manufacturer does suggest replacements of some wear items.

Plugs, PCV Valve, Oxygen sensors, coil pack, wires etc. included. (you get the picture)

I have an 02 Ranger automatic that I kept getting a #6 cylinder misfire as you described. Although driven daily including weekends and now showing 350K miles to prove it, with good regular maintenance my issue was an injector that when tested was not firing. Despite routine gas and injector cleaners being administered. I removed the injectors and sent them out for service where they measured before and after and #6 did not fire at all while others were all over the place.

The noticeable performance after the injector service was completed was unbelievable. Not that yours needs this, just sharing my experience. another time I had random misses and that resolved by replacing all 3 Oxygen sensors due to being over 100K miles old, this also resolved missing and at times cutting out during hard acceleration issues.

Point being, make sure your maintenance is up to date. To your question would a small oil leak from the valve cover gasket in that location cause it, most likely not. Gasket do wear and replacements will need to be done.

I too benefited from RonD's wisdom and advise however, lately I have not read any new posts from him.

I hope what I shared helps and keep us posted on your progress.

 

to start with whats the mileage? have you checked for codes? the IAC wouldn't cause a misfire in 1 cylinder. the spark plug looks fine and could be the coil pack or plug wire. to test a wire find one that will fit cyl 6 and exchange it with another. you could do that with a plug too. see what happens. i dont think its the coil because cyl 2 and 6 use the same coil. i'd pull the plugs on that side and see how they look. do they look they all the same? if the compression is low in cylinder 6 most likely its a burnt valve. look up how to do a compression test. cold motor and pull all the plugs. good luck!

 

Thanks for your thoughtful reply and insights. I’m at 247k KM’s; bought it used and unsure what was done by previous owner. I am behind on high mileage maintenance; apart from plugs and wires done a year ago, I haven’t changed anything that you’ve described. I try clean the MAF every time I do an oil change however.

I am leaning towards fuel injector like you said as it’s only one cylinder, ever. Will change my PCV this weekend as well as it’s cheap. Need to save up for new 02 sensors and a new injector. Don’t have a garage so hesitant to pull intake cover off as I use my truck for work everyday.

will update this thread when I make progress!

 

Thanks for the reply. Yes, it will throw a P0306 whenever it occurs. Been a few times where it flashed but didn’t stay.

had the code before and changed plugs and wires in response. I read somewhere that a wire touching metal like a manifold cover can cause misfires so I made sure I had em all loomed up snug.

Planning on a compression test in near future; just don’t have much extra cash for the kit at present. Will keep you posted!

 

you can disconnect the battery for an hour or so... it will clear codes.

 

Thanks for reply. I have a code reader and will clear the code whenever it pops up, after taking pics of the freeze frame data.