So my Pacifica, after a long road trip around a year and a half ago, had it’s check engine light come on. The meter read P0305, which is cylinder 5 misfire. When I got home, my local trusted mechanic replaced the coil and wire. Since then, the same misfire has occurred at least 4 times, and 3 of which he replaced the same parts (free warranty swap of the parts). The last time, he was determined that it wasn’t simply the parts going bad. I concur. It has now lasted roughly a month and the light is back on with the same code. The spans have been as little as a week between leaving the shop and the light coming back on. I personally don’t feel the car riding rougher than normal, but my wife does. I don’t smell gas, have odd colored exhaust, or any other issue. The only other thing, which idk if it’s related, is a clicking noise from the engine, which quickens with revving, perhaps the risers. What else could it be? I read that Chrysler’s go to is a valve spring retainer lock and a MAP sensor that accompanies it. I have no idea what that is. Any thoughts?
Try swapping fuel injectors.
Do a compression test.
“…mechanic replaced the coil and wire.”
I assume you forgot to mention that the spark plug was also replaced.
First I’d do a compression test. If #5 is within compression limits, I’d replace the spark plug first.
If that didn’t cure it, I’d swap the the #5 injector with #3 and see if the misfire moves to the #3 cylinder. IF no misfire occurs then it was the plug that was the problem. If the misfire comes back, but on #3 then it is the injector that’s bad.
Intermittant misfires on the 3.5L engine can be caused be carbon deposits on the exhaust valve seats. Bulletin # 09-010-06 involves installing revised valve spring retainer locks;
This bulletin involves rotating all engine exhaust valves, replacing the valve spring retainer locks with a new design to increase valve rotation at lower RPM, inspecting/replacing the MAP sensor (as necessary), and decarbonizing the combustion chamber
Sounds like this can be accomplished, without removing the head?
Piston at TDC, install air adapter into spark plug hole, and have at it . . . ?
Yes, remove the rocker arm shafts and pressurize the cylinders…
Your mechanic was 99% of the way there with the spark plugs out so a compression check should have been run to verify things are fine mechanically; and especially so considering that TSB about valve rotation.
Low compression can cause a misfire due to incomplete combustion so maybe the clicking sound is a spark jumping from the plug boot to the cylinder head.
Exhaust valves not rotating enough on their seats can have a tendency to burn also which leads to lowered compression which leads to misfires which leads to…
It’s a vicious cycle.
I’ll be taking it to the mechanic today, so I’ll let you know! Thanks
Still working this out. The dealer did a driving test and somehow determined the the head would have to be replaced.
My mechanic did a compression test both with the engine on and off and both had ample compression.
My next move is to determine whether the dealer did anything more than drive it metered, and want to charge 2k. Their paperwork does not show that they even did a compression test!
Dealer will remove/rebuild both heads for issue with 1 head? Not 100% certain if that is plan.
My mistake, yes you are correct. The right head is what they say needs to be replaced. There actually isn’t a problem with operating the vehicle. The only symptoms are the check engine light and the engine clicking. If I hadn’t explained it before, the clicking I was told was probably the risers and click faster upon revving. It’s more annoying than anything. Other than that, if the light wasn’t on, you’d never know there was a problem. It’s just strange that the dealer only did a road test. My mechanic was baffled at this. He has determined that the coil, plug, and wire are fine and that it holds compression. My fear is that if it IS the head, eventually a crack will get big enough to destroy the engine altogether. My mech says that taking the head off to see would be costly and may not solve anything. We are trying to figure a way to fix it without taking the whole thing apart. It may not be possible.
He can swap the injectors as said earlier to see if the code moves to another cylinder.
Finally got some clarity from the dealer. Apparently the rocker arm walks? To the side and is wearing out the head. The new head is a temporary fix because it will get worn again. The tech said that the rocker arm, as it turns, walks sideways, pushing on the valve guide crooked and wearing out the head. There’s no crack.
Reports to RepairPal for similar issues:
If you like the car, you might as well fix it.
Why does the head need to be replaced?
I would think a good machine shop should be able to get it going again
I would hate to say yea or nay on any engine repair without knowing what the compression numbers are. They’re described as “ample” but oftentimes that interpretation is not correct.
I am NOT a late model Chrysler guy (no desire to be either) and I’m not familiar with this particular problem. However, I have had some experience dealing with rocker arm issues on both cars and motorcycles.
Pics of the Pacifica units do not show any wave washers or shims on the rocker shafts and I wonder if the problem could be caused by lack of washers or shims?
One also wonders if oil feed holes in the rockers could be plugged up a bit due to extended oil changes and which could exacerbate the problem.
Just food for thought…
I recall replacing valve train components on 3.5 engines @ok4450. I’d have to look to refresh my memory, but if I recall, the engine used a rocker rail setup similar to the old 318, etc., with oiling through the shaft. The shaft would rotate in the towers, making the oil feed holes no longer align with the supply from the head. Starve the rockers, noise and wear follows. I think the bulletin Nevada linked here earlier has to do with updated springs and keepers to keep the valves rotating and cut the carbon on the faces.
When I was at the Chrysler dealer I was seeing intermittent misfires due to carbon on the valve seats. Today it seems this vehicle has valve train noise, this suggests there is a more serious problem.
Removing the valve cover for inspection should confirm the problem but an experienced tech will have confidence in his assessment based on passed experiences with this engine.
Keeping in mind my prior comment about not being a late model Chrysler guy I might pose this in regard to the comment about the rocker arms walking.
I note in the pic that on one side of the cylinder head that 2 valves are opened by one rocker arm driven by a single cam lobe.
What if the valve stem installed height varied on that one rocker arm (although applicable to all) since new due to an “I really don’t give a xxxx…” attitude by the engine assemblers* and in turn that could lead to the Y-shaped rocker trying to cant a bit with each valve opening. Continuing the progression this could lead to the rocker being tossed off kilter a bit each time and lead to it banging into the cam caps.
The same theory could apply to a hydraulic lash adjuster gumming up and sticking which could then lead to the rocker trying to cant a bit.
Just some more food for thought; or crumbs…
*Like assembly line vehicles are going to be assembled with precision anyway…