2009 Mercedes B200 persistant misfire at idle…
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2009 Mercedes B200 persistant misfire at idle…
Hi all, just bought a 2009 Mercedes b200 turbo with a cylinder 1 misfire. Previous owner sold it because shop was charging an outrageous amount to change the plugs and wires (suspected issue). I bought the car and changed:
Cylinder 1 spark plug: New
Cylinder 1/2 ignition coil: New
Cylinder 1 plug wire: Not replaced but tried cylinder 2 and 4 plug wire which are good.
Cylinder 1 fuel injector: Swapped with cyl 2
All of these made no change, and the parts I swapped to different cylinders didn’t cause misfires there.
What gives? Misfire counter slowly climbs at idle, evens out as rpm’s increase. Compression test was very hard to do and leaked pressure around the tool’s seal but spiked to 130+ with every compression stroke. No abnormal blowby.
Spark seems to be leaking back into the coil housing, I’ve caught it arcing off the housing and back through ECU connection which isn’t good. But what is causing resistance and stopping spark intermittently?
Cylinder 1 spark plug: New
Cylinder 1/2 ignition coil: New
Cylinder 1 plug wire: Not replaced but tried cylinder 2 and 4 plug wire which are good.
Cylinder 1 fuel injector: Swapped with cyl 2
All of these made no change, and the parts I swapped to different cylinders didn’t cause misfires there.
What gives? Misfire counter slowly climbs at idle, evens out as rpm’s increase. Compression test was very hard to do and leaked pressure around the tool’s seal but spiked to 130+ with every compression stroke. No abnormal blowby.
Spark seems to be leaking back into the coil housing, I’ve caught it arcing off the housing and back through ECU connection which isn’t good. But what is causing resistance and stopping spark intermittently?
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From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
Hi all, just bought a 2009 Mercedes b200 turbo with a cylinder 1 misfire. Previous owner sold it because shop was charging an outrageous amount to change the plugs and wires (suspected issue). I bought the car and changed:
Cylinder 1 spark plug: New
Cylinder 1/2 ignition coil: New
Cylinder 1 plug wire: Not replaced but tried cylinder 2 and 4 plug wire which are good.
Cylinder 1 fuel injector: Swapped with cyl 2
All of these made no change, and the parts I swapped to different cylinders didn’t cause misfires there.
What gives? Misfire counter slowly climbs at idle, evens out as rpm’s increase. Compression test was very hard to do and leaked pressure around the tool’s seal but spiked to 130+ with every compression stroke. No abnormal blowby.
Spark seems to be leaking back into the coil housing, I’ve caught it arcing off the housing and back through ECU connection which isn’t good.
But what is causing resistance and stopping spark intermittently?
Cylinder 1 spark plug: New
Cylinder 1/2 ignition coil: New
Cylinder 1 plug wire: Not replaced but tried cylinder 2 and 4 plug wire which are good.
Cylinder 1 fuel injector: Swapped with cyl 2
All of these made no change, and the parts I swapped to different cylinders didn’t cause misfires there.
What gives? Misfire counter slowly climbs at idle, evens out as rpm’s increase. Compression test was very hard to do and leaked pressure around the tool’s seal but spiked to 130+ with every compression stroke. No abnormal blowby.
Spark seems to be leaking back into the coil housing, I’ve caught it arcing off the housing and back through ECU connection which isn’t good.
But what is causing resistance and stopping spark intermittently?
At least you have a proven good cylinder compression.
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What else should I try swapping? Cylinder 2 would also be misfiring if ECU signal was poor, so I believe the issue it between my new coil and new spark plug. Plug wire is the only thing there but I’ve tried swapping it already with 2 and 4…
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From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
process of elimination
Your problem cylinder is proven good - If you have second thoughts: bore scope.
If you spark is good then swap 2x injectors around... bad one may be partially plugged up by contaminants or ECU injector driver is toast.
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It’s not a dead miss at all, just a very lumpy idle felt inside the car. Puts the throttle valve into limp mode after too long of driving. Completely removing spark from cylinder 1 makes it considerably worse
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W212 MY'14 M276-3.5NA @75kMi
Verified good spark with a second plug grounded outside the head. Nice blue spark but tough to tell how/if it’s intermittent. Tried swapping injector 1 to cylinder 2, misfire did not follow the injector nor did cylinder 1 clean up with cylinder 2 injector.
It’s not a dead miss at all, just a very lumpy idle felt inside the car. Puts the throttle valve into limp mode after too long of driving. Completely removing spark from cylinder 1 makes it considerably worse
It’s not a dead miss at all, just a very lumpy idle felt inside the car. Puts the throttle valve into limp mode after too long of driving. Completely removing spark from cylinder 1 makes it considerably worse
This confirms your ECU drivers are working ok.
Your injector likely ok
Your ignition likely ok
but then Limp mode!?!
Ignition does not LM... throttle body does.
Any LM specific code??
No code... no LM.
Last edited by CaliBenzDriver; Apr 11, 2025 at 06:38 PM.
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Last edited by Leviathan888; Apr 11, 2025 at 06:54 PM.
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Out Of Control!!
Joined: Apr 2019
Posts: 11,958
Likes: 6,802
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
Thread Starter
Newbie
Joined: Apr 2025
Posts: 13
Likes: 1
From: Vancouver island BC
Thread Starter
Newbie
Joined: Apr 2025
Posts: 13
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From: Vancouver island BC
Here’s where I’m at right now: ECU signal should be fine going to coil, being a waste spark system if it was not there would be a miss on cylinder 2 also. I backprobed the connector on the ignition coil and to my surprise have high voltage that arcs to my fingers! This is the ECU 3 pin connection on ignition coil. This means (to my knowledge) spark isn’t being fully utilized on cylinder 1 and is leaking back to low voltage side and housing of the coil.
I’m about to try probing that 3 pin connection without being hooked to the coil, should confirm if the problem is coil-downwards. No way the ECU would be able to produce spark-levels of power at that signal pin…
I’m about to try probing that 3 pin connection without being hooked to the coil, should confirm if the problem is coil-downwards. No way the ECU would be able to produce spark-levels of power at that signal pin…
Out Of Control!!
Joined: Apr 2019
Posts: 11,958
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From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
Here’s where I’m at right now: ECU signal should be fine going to coil, being a waste spark system if it was not there would be a miss on cylinder 2 also. I backprobed the connector on the ignition coil and to my surprise have high voltage that arcs to my fingers! This is the ECU 3 pin connection on ignition coil. This means (to my knowledge) spark isn’t being fully utilized on cylinder 1 and is leaking back to low voltage side and housing of the coil.
I’m about to try probing that 3 pin connection without being hooked to the coil, should confirm if the problem is coil-downwards. No way the ECU would be able to produce spark-levels of power at that signal pin…
I’m about to try probing that 3 pin connection without being hooked to the coil, should confirm if the problem is coil-downwards. No way the ECU would be able to produce spark-levels of power at that signal pin…
You've switched ypur coil around to prove it good.
Double check you have good Grounds circuits.
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No grounds actually run to the coils (I think) just 12v power and 2 signal wires that ground-switch the coil to create spark. And housing shouldn’t need to be grounded either, correct?
Last edited by Leviathan888; Apr 11, 2025 at 09:20 PM.
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From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
New coil actually, OEM Bosch purchased yesterday. When disconnected from the ignition coil the harness no longer has spark to it (good) and I tested all the wires back to the ECU. So that end of the circuit is fine. Next I’m gonna try unhooking cylinder 1 wire and just grounding that coil tower right to the block. If spark leakage on the housing and ECU connector disappears, it must be the plug wire that has too much resistance.
No grounds actually run to the coils (I think) just 12v power and 2 signal wires that ground-switch the coil to create spark. And housing shouldn’t need to be grounded either, correct?
No grounds actually run to the coils (I think) just 12v power and 2 signal wires that ground-switch the coil to create spark. And housing shouldn’t need to be grounded either, correct?
The primary is usually supplied with +12v Key and switched to GND by ECU trigger or coil does it's own local primary side switching to GND.
It is true that if coil high-voltage has no path to exit it will discharge to GND everywhere possible. Sparkplug discharge path must be effective else coil gets bridged internally to become marginal.
Last edited by CaliBenzDriver; Apr 11, 2025 at 10:00 PM.
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Also I backprobed the cylinder 3/4 ignition coil and got the same shock off the ECU signal pins. No misfire there so I believe that clue can be removed as I assume it has to do with the electromagnetic field around the coils. Only happens when my hand/another finger is touching a ground point.
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W212 MY'14 M276-3.5NA @75kMi
Very interesting, different from what little I’ve found! The coils have been floating while I’ve been testing because I was unaware of this. In order to properly mount them once again I had to revert plug wires to original locations. After cleaning up the mounting surfaces with some emery cloth, there is still no change to the idle.
Also I backprobed the cylinder 3/4 ignition coil and got the same shock off the ECU signal pins. No misfire there so I believe that clue can be removed as I assume it has to do with the electromagnetic field around the coils. Only happens when my hand/another finger is touching a ground point.
Also I backprobed the cylinder 3/4 ignition coil and got the same shock off the ECU signal pins. No misfire there so I believe that clue can be removed as I assume it has to do with the electromagnetic field around the coils. Only happens when my hand/another finger is touching a ground point.
How mant miles is this setup ?
I'm wondering if this "misfire" is NOT IGNITION related but well something else...
> Moving on:
Are you confident about your new coil + plug (+ wire) ?
We nearly well trust your injectors + ignition + bore...
then what else is in store to cause this misfire with would be Limp-Modes...
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makes your hair stand up
How mant miles is this setup ?
I'm wondering if this "misfire" is NOT IGNITION related but well something else...
> Moving on:
Are you confident about your new coil + plug (+ wire) ?
We nearly well trust your injectors + ignition + bore...
then what else is in store to cause this misfire with would be Limp-Modes...
How mant miles is this setup ?
I'm wondering if this "misfire" is NOT IGNITION related but well something else...
> Moving on:
Are you confident about your new coil + plug (+ wire) ?
We nearly well trust your injectors + ignition + bore...
then what else is in store to cause this misfire with would be Limp-Modes...
Only reason I’m working with ignition is because earlier with an inline spark tester I saw very intermittent flashes. Probably due to my test setup and symptoms have disappeared but still though I noticed some weird gaps. About to test a plug outside the block again but also not sure it’s ignition.
Havnt completely ruled out injector but the miss didn’t follow when I swapped 1 and 2, and cylinder 2 runs clean now and before the swap.
Compression was very difficult to check, my tester has nothing to thread in with a socket so relies on hand-tightening of the rubber hose to seal. Being that access is poor I got the tool tight but air was audibly leaking out while cranking. Compression shot to 130+ psi with every stroke though before leaking back out the plug hole, making me believe theres good pressure.
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Here’s the link to the video of my compression test.
https://drive.google.com/file/d/1oc5...w?usp=drivesdk
https://drive.google.com/file/d/1oc5...w?usp=drivesdk
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W212 MY'14 M276-3.5NA @75kMi
listening to your slow crank and hearing about your weak spark and wonky throttle...
how about you charge your battery and measure ALT output is near 14volts.
No chance this is related to Crank sensor.
how about you charge your battery and measure ALT output is near 14volts.
No chance this is related to Crank sensor.
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Will charge battery and verify alternator output tomorrow.
I’m starting to suspect a sticky valve on cylinder 1, in that compression test video one of the strokes loses pressure way too quick - different from the rest. I’m gonna pick up a vacuum tester tomorrow. Check the intake manifold vacuum and see what that tells me.
I’m starting to suspect a sticky valve on cylinder 1, in that compression test video one of the strokes loses pressure way too quick - different from the rest. I’m gonna pick up a vacuum tester tomorrow. Check the intake manifold vacuum and see what that tells me.
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Just performed a vacuum test and the car passed just fine. Holds exactly 18.5 Hg at idle, with the gauge connected to a port on top of the intake manifold. Back to ignition or fuel?!?
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From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
trust
Last edited by CaliBenzDriver; Apr 13, 2025 at 06:49 PM.
