Could A Bad Alternator Cause Misfire?
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E63 2012
Could A Bad Alternator Cause Misfire?
I own a 65k miles 2012 E63 w/ M157. I had misfire issues with cyclinder #6 and #7; the car shakes when it's idling and the rpm is not stable when I start accelerating from 0 mph; my mechanic told me it's the bad coils, so he replaced all the coils and sparkplugs, but the misfire and CEL came back on after the misfire is gone for about a week. I had an obd ii scanned and it's cyclinder #6 and #7 again. Then I left about a week for spring break and the car wouldn't start because the battery is drained, and I jumpstarted her and drove her to my mechanic, and he told me that the alternator is dead, and it could also be the reason that caused the misfire. Anyone had similar issues that wanna share? This is my only car so I really wanna fix her. Thank you guys.
Last edited by Rushing_Nooby; Mar 18, 2023 at 07:18 PM.
Thread Starter
Newbie
Joined: May 2022
Posts: 4
Likes: 1
E63 2012
Should I replace the alternator or I heared that it's usually the voltage regulator failure. My mechanic told me that the alternator is really hard to reach, and he have to remove the turbo first to replace the alternator.
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Joined: Sep 2018
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From: New Orleans Area
2015 E400 Sedan
Frommy understanding the ECM looks at the output from the crank sensor and compares to some stored waveforms within
If they do not match it itt looks at what cylinder was supposed to fire at that time and throws up a the check engine light.
Now a bad alternator (or anything drivenby engine Serpentine Belt) can cause additonal uneven torq demand from crank.
The crank sensor sees these as misfires since crank was slowed down for quick bit and the wave form does not match what it expects
TO test - clear misfire codes.
Remove serpentine belt
crank engine and watch temps and pressures etc but run for a min or so and see if it throws code for misfire.
IF not maybe something with pulley on front needs some love sticky bearing in idler pulley or tensioner spring is too soft and worn now so belt bounces.
Alternator going out and has bad spot or soemthing.
If they do not match it itt looks at what cylinder was supposed to fire at that time and throws up a the check engine light.
Now a bad alternator (or anything drivenby engine Serpentine Belt) can cause additonal uneven torq demand from crank.
The crank sensor sees these as misfires since crank was slowed down for quick bit and the wave form does not match what it expects
TO test - clear misfire codes.
Remove serpentine belt
crank engine and watch temps and pressures etc but run for a min or so and see if it throws code for misfire.
IF not maybe something with pulley on front needs some love sticky bearing in idler pulley or tensioner spring is too soft and worn now so belt bounces.
Alternator going out and has bad spot or soemthing.
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Joined: Jun 2021
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From: Fleriduh
W212 E63S Wagon - GSL580 - E63 - E350 - C300
Few months back I had some odd things...random mis-fires and what not. Turned out to be the alternator. We opted to replace it with new OEM - thankfully. Had I opted for the pickup only would would not have noticed the bad bearing and massive load on the belt due to the bad bearing.
