Originally Posted by jeepman917
Sorry for late reply - I have 5500 miles. Willx believes it may just be Hemi Resonance - I asked him - and he's said he's experienced this type of noise in the Hemi's. Hate to say it - it is an american car - and I've been thinking that perhaps I'm too critical of it. Don't know - shouldn't have this type of issue with a $55k vehicle. I will have my dealer address with the AC at the oil change - which will be this week. Lets keep each other posted Peter! Good luck! Charlie
Hmm...the only resonance I know of from the Hemi has to do with the MDS system. And that will only happen with the MDS active...which it isn't at idle.
I've traced it down to being the engine itself vibrating at idle and setting off a body boom type of resonance. With the A/C on and in gear it vibrates a bit more because of the load, making it worse.
I've been in about 10 others and, while a couple had it a little bit, nothing like mine. I'm generally not that overly critical of this kind of thing, but when everyone who has been in kind suddenly goes "what the hell is that" when it idles down and really resonates, eh...I think it's a problem.
So...I dug further with a scan tool just to see how the engine was running...
Looking at the long-term fuel trim at idle, in gear, I'm seeing +4.8% on Bank 1 and +8% on Bank 2. This means the PCM is adding those percent more fuel than the stock mapping to compensate for detecting that it is running lean. That rather shocked me...on an older motor I might not be bothered by this but on a motor with less than 1000 miles on it, this is odd. Most new, tight engines will show either (at most) +/- 3% at idle, with many being on the slightly negative side. That much positive fuel trim tends to indicate a vacuum leak, valve issue, or ignition/compression problems leading to a weak cylinder or 2. I also noted random scattered misfires (not enough to throw a code...scattered 2-5 counts on various cylinders). I'm tending towards thinking vacuum leak in the intake manifold, somewhat closer to the bank 2 side (explaining the difference between the two).
Now...if I can only get the dealer to investigate this...many won't simply because it isn't throwing a code yet (and won't until it gets to the north side of +20%). This is what drives me nuts about this kind of thing--it won't throw a code until it's really severe, but these levels aren't "normal" for a new engine either. And, yes...this kind of thing will affect idle quality and can set up resonances like the one I'm getting.