I have a ‘17 grand Cherokee, a little over a week ago a message would come on the dash stating “Stop/Start unavailable” (the feature that cuts off the engine when idle) intermittently, probably only about half the times I drove it for a few days. Little Google search told me it was probably a battery problem in the system, and since I always deactivate it anyways, I ignored it. The engine light came on eventually, and diagnostic came up code P0305, cylinder 5 misfire. Mechanic changed the 3 plugs and coil on the 3 cylinders under the intake. Next day, engine light came back on. Same code. I took it back, and was told car is running fine and they said to try filling the car with premium gasoline. Did that, light stayed off for about 48 hours, even through a trip out of town (500 miles) and was fine. Got back home, light came on again, same code. I took it back and they replaced remaining 3 spark plugs, but I am sure it’s going to come back again since it’s a cylinder 5 misfire. Does anyone have any idea what could be going on with it? It’s giving me a lot of stress
Could be bad piston rings in #5, bad valve seal in #5, leaking head gasket, bad injector, failing camshaft… just to name the top choices.
Your “parts changer” mechanic should have run a compression test.
Assuming this is a Pentastar V6. They have a lot of cylinder head and valve train issues. Had a similar code on a Dodge Journey that ended up being a bad lifter.
There is a wealth of information available in the engine control computer that is stored whenever a fault code is set. That information can steer the mechanic in the right direction as to whether the trouble is ignition related, fuel related, or mechanical in nature. Either your mechanic does not have the equipment or the knowledge to access that information or to do a proper diagnosis.
Suggesting that someone try a different grade of gasoline to correct a single cylinder misfire is crazy. I recommend you ask your friends, neighbors, coworkers for the name of a reputable garage.
I have seen so many Jeep 3.6L engines with internal engine failure with cylinder 5 or 6 misfire codes come in that as soon as we/I pulled that code I stopped and referred them to the dealer, this was mostly in the mid to late 2015-2018’s, still saw the same thing a few years later but not as much… got bit replacing spark plugs and coil(s) once and found it had internal damage, won’t happen twice… I did the right thing and refunded all money for the work done since it did not “fix” the running issue, even though the plugs were worn and needed replacing…
Looks like there is a possible class action lawsuit on the 3.6L V6 (yours may not be involved) that you might want to check into… Also I would contact the dealer just incase they are helping with repairs…
Don’t get your hopes up for retirement money, the lawyers are about the only ones that make money on those things… example: a friend of mine was involved in a big class action law suite and after years of waiting he finally got his “BIG” check for a little over $16.00 his share…
It’s Lawsuit, a suite is a place to stay in a nice hotel.
Thank you sir, corrected now… spelling is NOT my strong suit and spell check and autocorrect has gotten me in trouble a few times… haha
Class action lawsuits are not all that bad even though I always thought they are useless myself. It finally got us a new Hyundai engine when our’s seized at 140K miles. It started burning oil at 60K miles and I have poured too many qts of oil in that engine to keep it going (1qt/400 miles) but at least we do have a new engine now.
And the nice new office suite the class action lawyers can afford once they win.
While many CALs yield only a meager payout to the claimants, there are some–like yours!–that are well worth joining.
The best one that I ever joined had to do with price-fixing of Cathode Ray monitors/TVs by a few manufacturers. On a whim, I decided to join that CAL, and–to my great surprise–the following year I received a check for over $300 for my claim regarding 3 of the covered monitors/TVs.
Hi! I have the same exact problem with my Jeep, except instead of cyliner 5, mine is a cylinder 3 misfire. Auto start/stop service warning came on, but turns off once I restart the vehicle. And then shortly after, I got a P0303 code. We changed the spark plugs, and the check engine light turned off. Light came back on about a month later, so we changed the ignition coil. Then the light went off, but came on a month later again. Now the light has been on continually for about 2 months now. No real noticeable issues with how the engine runs. I do notice a loss in power, but that’s expected when you don’t have a cylinder firing. Oil looks good, coolant looks good, no overheating, no knocking. But whenever the check engine light is on, the auto start/stop is fine. I only get the auto atart/stop unavailble warning whenever the check engine light is off. So odd.
So just wanted to see if you ever figured out the problem! Thank you.
You can’t assume both cars have the same cause.
You need a compression test to determine the cause of the misfire. Since the ignition for this cylinder has been replaced, the compression test will tell you if it is a mechanical problem.
Many possible causes beyond spark plug and coil for a misfire. And the misfire might not actually be on cyl 3. The computer monitors the crankshaft to see if it accelerates as expected after each spark plug fires, but it can be confused when it notices a lack of crankshaft acceleration which spark plug firing it corresponded to, depends in part on nature of engine load at the time. Suggest ignition system test & engine compression test on all cylinders.
Hopefully OP will post back what their shop discovered.