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Discussion Starter · #1 ·
I took my 2008 3.5L SXT to a reputable shop for a new timing belt at about 105K miles. I had the water pump replaced in the process but not the crank or cam seals. A timing belt tensioner was replaced for leaking fluid.

Immediately following the new belt installation, and for the next 1000 miles now, I have a rough idle at 550RPM and very noticeable engine vibration when cruising or accelerating around 1500RPMs. The rough idle is only after warm-up, higher revs at cold start are not rough. The car accelerates well and is as responsive as it ever was.

The mechanic suggested driving a tank of gas and watching for a check engine light. The light came on and he read the code, 330 I think, as "random misfires." He reset the computer and performed a procedure he called "cam synchronization" via the computer. I checked gas mileage over the next tank and got 25.9, which is only slightly less than the 26.7 I measured years ago. There is no noticeable loss of performance.

No change!, the car still idles rough and the engine feels like it has its own subwoofer blaring something below 50Hz only at or near 1500RPM. The check engine light finally came on again and then went back out but I haven't had the time to get it rechecked.

I read other posts that cited "cam phasers" and spark plugs as possible causes of similar rough running symptoms, but the onset of this vibration was sudden and immediately following a day in the shop, to me appears to be a result of the work that was done. I don't know if this engine has "cam phasers".

I plan to get the plugs changed soon but don't feel this is the cause. I'm not sure how to interpret the "random misfires". To me, it would seem to indicate that the misfiring is not associated with a particular cylinder.

Is it possible the timing belt is not properly timed, but so close as to not cause major clearance problems? Is there some mechanical engine balancing device that may have been disturbed in the belt change process?

My mechanic seems to need your help as much as I do.
 

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No cam phasers in the 3.5L, that's for variable cams.

Sounds like one of your cams is out of time/a tooth off. Easy enough to do, there are lots of things that can get misaligned in a timing belt replacement.

Something to consider before tearing it down is a cracked plug or a vacuum leak.
 

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Discussion Starter · #3 ·
I just went out and read the stored code as 0300, I assume that's what the code was that the mechanic read 500 miles ago, rather than 0330. Thanks for the reply, "Sounds like one of your cams is out of time/a tooth off." That's one of the possibilities that comes to mind. Anyone know how many teeth on the cam's sprocket? The larger the number, the more likely this possibility (a smaller number of teeth would be more drastic change in timing.)
 

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There are two cams, one on each head. The belt runs between the crank, past the tensioner, and to each head.

There are three things needing to be aligned, each cam (there are alignment marks) and the crank. It's pretty easy to be a little off (unless you actually pay attention, lol).

It isn't so much "How many teeth" as much as getting those three elements aligned to their proper marks, and be on the correct stroke.

The teeth on the belt and sprocket are actually fairly large, fwiw.
 

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Discussion Starter · #5 ·
I asked about number of teeth on the sprocket because misalignment would have to be in increments of teeth. At 360 teeth on the sprocket increments would be one degree per tooth, and at 30 teeth on the sprocket increments would be twelve degrees per tooth, much more drastic and likely to cause performance loss, gas mileage loss and worse, clearance issues for valves and piston.
 

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The picture is fairly representative of the number of teeth, as I recall. I have changed one before, myself.

 

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No cam phasers in the 3.5L, that's for variable cams.

Sounds like one of your cams is out of time/a tooth off. Easy enough to do, there are lots of things that can get misaligned in a timing belt replacement.
I agree. It might be that only one cam sprocket is off by one tooth so that one is timed with the crank and one isn't. I'd have the mechanic re-check his work. Are there any access "windows" in the timing belt cover to allow the marks to be checked without removal of the cover? Some cars have that, some don't.
 

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Like the others, I agree on it being possibly off a tooth. Not hard to do as I just did mine on Thanksgiving Day. The real drag is you have to pull all of the crap off to see if it is off or not..Not all, but the fans, serpentine belt, tensioner, harmonic balancer and the covers..Good part is it could be fixed relatively quickly and without any cost on parts..

I did mine twice as I didn't like the look of it the first time and the second it was a bit better..Just had to wait on the drive belt tensioner to bleed down on try number two..

Griz
 

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Discussion Starter · #10 ·
Really appreciate the input, guys. Scheduled to see the mechanic again on 12-10 and will post results afterward.
 

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Discussion Starter · #11 ·
Well, I dropped the Charger off with the mechanic today and he concurs that he probably misaligned a tooth on one cam. He's tearing it down to check now. More later...
 

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Discussion Starter · #12 ·
When I took the Charger in the mechanic had already decided to tear it down and check the timing belt. He says he found the passenger side cam off time by one tooth, retarding the cam. He retimed the cams and the problems cleared up.
 

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p0300 and idling rough problem in the 3.5

FYI if you have a p0300 and rough idle after have the timing belt changed i have learned that the right cam shaft needs to be turned 1 tooth ahead when putting the timing belt on not sure the logic due the cam sensor is on the left head but i had the problem after replacing my own belt on my 2006 charger after trying many things i reset the belt on the right cam 1 tooth ahead and it runs great just thought i would pass the info on.
 
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