kavik

So I am having a misfire issue I (and mb techs) cant figure out on my 2013 C63. My car is supercharged, but I recall reading about this same specific circumstance issue in some N/A cars in the past, but cant find the threads anymore. When driving easy on highway, usually after car has run for 20 min or so, at low rpm and around 70mph , if I lazy foot it at 1/5 to 1/4 throttle to speed up just a little, I'll get a general misfire code and it will shut down right bank of cylinders. It's always at low rpm, very light gas pedal, usually 7th gear and sport + (which I usually drive in). If I pull over and restart I'm fine. Driving hard its no problem. Have done leakdown, checked all cylinders, checked manifold, all new coils, ecu reprogrammed, etc, fuel trims are right on. It's running off normal O2 sensor data at low speeds and rpms. O2 sensors are good. Just gives general cyl misfire code, usually on #5.

Any ideas??

BalanBro

Just speculating, but could it be timing related? Like crank position sensor, or even a failing cam adjuster? Do you get that cam adjuster rattle at startup?

hachiroku

what tune do you have with your supercharger? is this a weistec kit and tune? need more specifics.

kavik

Its an ESS charger started with their canned tune and was then dyno tuned. The misfire code is a generic cyl X misfire. Too hard to duplicate on dyno. I specifically remember some issues with some N/A setups also happening only at low rpm / light throttle from a while back so I'm wondering if it could be engine related and not a S/C issue.

hachiroku

if an NA motor and misfire at low rpm light throttle and with aftermarket tune...if your plugs, coils, injectors, and intake manifold are in good shape, it would be the tune.

as far as supercharged...same items above should apply. if all your mechanicals are in order, then start looking at your tune, but if a specific tune is known for being problematic, then that is a whole different topic entirely.

kavik

Would the issue be too lean, rich or timing? From what I understand, the first part of the tune (wher le issue is) runs off the o2 / maf data and then when rpms get higher / more throttle it runs off the programmed s/c fuel curve?

hachiroku

the Bosch Motronic 9.7 is a volumetric efficiency computer. o2 sensor data is used at all times. the computer is constantly adjusting fuel and timing for safe and optimal running conditions. if the tune is not dead perfect, can cause calculation issues.

i'd rule out all mechanical items first as generally speaking that is the easiest to do.

hachiroku

in regards to misfire...you can have a rich misfire or a lean misfire. was the tune supplied using Dimsport or HPTuners?

Dogtag114

I just picked my car up yesterday from repair of similar symptoms. For me, the camshaft adjuster unit and position sensor were replaced. Works great now and also fixed an issue I had with some mild stuttering between 1-2k rpms.

kavik

Hp tuners. My long term fuel trims with the tune are 1-2%. That's interesting about the camshaft adjusters. Did you have any specific error codes or how did they diagnose it? And it was only low rpm / light throttle? My car has 65k on it. I drove it the other day and manually kept rpms above 2000 and had no issues....

hachiroku

if HPTuners, you can datalog your cam phasers. If they're moving and sweeping as your map is requesting without error code, those won't be the problem.

your LTFT's are no more than 2% so you're good on tune generally speaking. there is a region where the factory computer can cause misfire issues when tuned. this is the 1,500-2250rpm region at high to full throttle. it takes a lot of work and is difficult to get that misfire tuned out. the computer basically doesn't like the values it's working with so juggles between pig rich to lean which can cause misfire. i spent most of my time diagnosing that region of my tune where as everywhere else was perfect.

Dogtag114

Since last July, I had the "lungy" feel only with light throttle between 1-2k rpms. I just used manual more and avoided it. It started soon after my headbolts were replaced.
One day I had obvious horrible misfires and pulled over, restarted the car and then was fine for a month. The code was general misfores.

Then one night it happened three times, same issues and code, so I took it in.