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Cylinder 3 Misfire Fixed Itself?

My 2014 T&C with approx. 63,000 miles on it felt like it was running rough.

On Nov 28 the check engine light comes on- code is a misfire on cylinder 3. We bring it to our mechanic- he finds a rodent nest under the intake manifold (amazing because this thing gets driven A LOT), found #3 ignition coil defective, and recommended replacing spark plugs while he is in there (for maintenance). Clears the mouse nest, removes and replaces intake manifold, premium gasket set, ignition coil, and spark plugs; cleared code and says it drives well. I pick it up and still seems to run a little rough, but assume I’m paranoid and decide to drive it home and see how it does.

Next day, load kids in, start van, wait for hubby to get in and the check engine lights comes back on. Mechanic says bring it to Dealership, it may be a recall like on earlier years. (Spoiler alert- the recall was 2013 and older and only for cylinders 2,4,6).

Dealership write up says they swapped ignition coils and same misfire, OHM test injector- passed test. compression test-Cylinder 3 has intermittent compression, “Perform inspection of valves intermittent intake closure popping through intake manifold. POSABLE GUIDE OR VALVE SPRING PROBLEM. RECOMMEND CYLINDER HEAD. CUSTOMER ADVISED AND DECLINED”.

Now this is where it gets interesting- we drive the van for the two weeks we are in town between thanksgiving and Christmas, so we can decide over our holiday to either fix it and keep it or to replace the vehicle. We get in the van on Christmas Eve to drive to the airport, Christmas miracle- the van is running better AND the check engine light is off.

It’s now January 30, the van is still, seemingly, running fine and the check engine light has not come back on….it’s hard to believe this is really just a Christmas miracle…but what other explanation exists?! Just something wedged in their that cleaned itself out? Or something wedged in there now that isn’t being burnt out, but when it is we will have catastrophic issues…. Please tell me the theories!?

How often do you change your engine oil, both in terms of time (every XX months) and in terms of mileage (XXXX miles)?

The first few years (2015-2018) in the vehicle we kept the miles pretty low, so it was probably around 6-9 months and 8000 miles. In the past 1.5 years it has probably been closer to 4-6 months and 7000 miles. We use synthetic oil.

I thought about irregular or too long change intervals and possible sludge formation, which might have resulted in valve hydraulic lifters getting stuck.
Probably not the case since you seem to keep it under control.
I’ve read that some of Jeep engines had issue with valve spring breakage, but I do not know much about Chrysler products to make a diagnosis and that condition would not cure itself magically.

The folks at allpar.com’s minivan forum might have some ideas. I’ve found help there for some of my Chrysler minivan questions. Good luck and please keep us informed.

Ray (of Best of Car Talk’s Tom and Ray) mentioned something called TCS == Toyota Camry Syndrome when talking to a caller who had a Camry engine performance problem. Apparently certain Camry’s at the time (this would have been 1990’s models I expect) were plagued by sticking valves. Something like that would likely be caused by valve guide or valve spring problems.

It certainly seems possible something like that could correct itself.

https://www.cartalk.com/radio/call/201531-call-03

In the old days it was common for cars that sat a lot to have sticking valves. Sometimes more frequent use would unstick them. Sticking piston rings were also common and there were many products on the market to unstick things. Shaler’s Rislone was a popular one. Both Valvoline and McMillans Ring Free oil were also advertised to free up valves or rings.