General Question on C63AMG (W205) Misfires
Thread Starter
Senior Member
Joined: May 2019
Posts: 313
Likes: 17
From: TEXAS
2017 AMG C63, 2001 C5 Corvette
General Question on C63AMG (W205) Misfires
Hello everyone,
I’ll start with my question first. How do you KNOW if your car has misfires, or IS misfiring?
I read posts about people with tunes saying they swap their plugs because they had some misfires. I just got a Tune and all is running fine, as far as I know, but I have no idea if a misfire is something you Easily will Feel, or Notice?
Trying to understand How One Knows their Car is Misfiring. Also, how bad is it for your car? I know it’s not good, but not sure what level or amount of misfires is cause for real concern?
And is changing the spark plugs the way to resolve a misfire? And how do you know doing that swap would fix it?
I have 22,000 miles and I heard the 20,000 mile mark as a time to consider swapping plugs.
Thanks
I’ll start with my question first. How do you KNOW if your car has misfires, or IS misfiring?
I read posts about people with tunes saying they swap their plugs because they had some misfires. I just got a Tune and all is running fine, as far as I know, but I have no idea if a misfire is something you Easily will Feel, or Notice?
Trying to understand How One Knows their Car is Misfiring. Also, how bad is it for your car? I know it’s not good, but not sure what level or amount of misfires is cause for real concern?
And is changing the spark plugs the way to resolve a misfire? And how do you know doing that swap would fix it?
I have 22,000 miles and I heard the 20,000 mile mark as a time to consider swapping plugs.
Thanks
Out Of Control!!
Joined: Nov 2018
Posts: 11,403
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From: San Francisco Bay Area
2019 C63CS
Typically misfires are indicated by a blinking CEL light followed by it staying on, but it could also be that the CEL is just coming on w/o blinking if it was a quick misfire. I've had that with my RS5 when it misfired under load at high rpms. All the sudden I had the CEL on, but didn't notice anything. Only after reading out the codes later did I know it was a misfire. Generally the engine will run rough and shake during misfires. There can be several causes for misfires. Carbon buildup, bad spark plugs, malfunctioning coil packs, malfunctioning or leaking fuel injectors, malfunctioning fuel pumps just to name the most common. It has to be properly diagnosed to fix. Replacing the spark plugs if the misfires occur due to a leaking fuel injector obviously won't fix anything. I'm not entirely sure how bad it is. The misfires can lead to carbon deposits in the combustion chamber and on the spark plug, causing further issues down the road potentially. A rough running engine is probably not a good idea, especially under load. I've gone through an episode of cold start misfires on my RS5 due to a failing fuel pump. I usually turned it off right away and started it fresh which then temporary fixed the misfire. Once the fuel pump was replaced, the misfires went away and no other issues resulted from it.
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Joined: Mar 2008
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C63s Cabriolet, BMW M4, Civic
It depend. A misfired cause by bad part like plugs, injectors, fuel pump, coils ... etc then you can definitely feel the engine idle and run rough. If you talking about misfired due to tuned because air intake temp is too high and cause your air fuel ratio out of spec... etc then it hard to fell it but you can see definitely see it on the dyno graph where the lines spike or drop. A bandaid fix would be change to 2-step colder plugs.
Thread Starter
Senior Member
Joined: May 2019
Posts: 313
Likes: 17
From: TEXAS
2017 AMG C63, 2001 C5 Corvette
Thanks so much. I appreciate those detailed answers. I know what a misfire is, but it’s good to know if it happens, you likely will know by the triggering of a CEL, or running rough.
