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Spark plug fouling trouble. I have a 2008 Chrysler 300C with the Hemi.


Cylinder #7 misfired (codes P0307 and P1417) and wouldn't work. Spark plugs were fouled (black material), so I believe the/a plug wasn't firing due to fouling. I cleared the codes, wiped plugs (reinstalled same plugs) and engine is running great again. Ran leakdown test on all cylinders and #7 was the second-lowest for leakdown (2.78%), but it did have crusty looking valves (I have a video scope).


Two other cylinders had fouled plugs (#1 and #4) and they had the two highest leakdown readings (8.3% and 6.11%, respectively). (Cylinder #1 also looked to have a small amount of metallic material around the edge of the cylinder, as a side note.) The other cylinders had 3.89%, 4.44%, 2.22%, 3.33% and 4.44% leakdown readings. Could hear air coming from the dipstick hole so assuming that ring wear is allowing air and maybe oil by them, but the leakdown results aren't alarming on their own for its age.


All three of the fouled and/or higher-leakdown cylinders are the ones deactivated when in MDS mode (#6 is also deactivated, but looks great), which seems like too much of a coincidence. Fouled plugs could be from oil or from too much fuel, apparently. I'm wondering if there is an MDS issue or a fuel issue or something else I should check, or might I just be experiencing normal ring wear allowing oil into the ignition area?


Have you experienced something like this? Any tips? I am trying to work on it myself for the first time and enjoying the process, but would love to see if anybody else can help me shorten my learning curve on this issue.


Thanks in advance!
 

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Maybe someone else will chime in with more info. I'll just add that unless you do a lot of long trips, I'd suggest you consider deactivating MDS with a handheld tuner as a relatively simple and painless fix.
 

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Maybe someone else will chime in with more info. I'll just add that unless you do a lot of long trips, I'd suggest you consider deactivating MDS with a handheld tuner as a relatively simple and painless fix.
Thank you. Never thought to do that. I have a tuner for my other vehicle, but not for the 300C. Do you have any suggestions on good ones?
 

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Personally, if all you want is to disable MDS, I'd just search Cragslist, eBay, and Mopar online forums' FS threads for a used unit, anything compatible with your car that is capable of MDS disable. If you want new, either a Diablosport Predator 2 or an Intune i3 should do the trick.
 
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