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I have a 2008 C300 4Matic. I’ve had a rough acceleration for a while and every time I’ve tried to scan I’ve had no luck. However today I finally got one for the code in the title, MB specific code was 0987. I thought this was weird since I know I just replaced the coils and plugs, but not impossible I got a bad one out of the box. I swapped the coil from cylinder 4 to cylinder 1 and vise versa in hopes it would be that simple, but obviously since I’m posting here it wasn’t. After clearing codes and driving for 20 miles to see if the fault switched to cylinder 1, it did not. The connector doesn’t look dirty either and I actually just cleaned them with some electrical contact sprayer a few weeks ago, thought I could try again.
Where else should I be looking for the solution to this code? Not a lot of information out there on it, and when there is it always seems to be as simple as swapping out the coil.
First if you only swapped coils and didn't do spark plugs that is a must since you have only done the coils a spark plug could still be a issue.
After that if you still have a misfire and a code I would then do a fuel injector swap as it's very possible that one could be leaking and causing a rich misfire. Also you can do a compression test of all the cylinders to rule out internal wear or damage.
Weather you do the injector swap or the compression test first would depend on which is easier to do IMO. It's something you should try to fix our it can cause you catalyst too get saturated and need to be replaced which is much more expensive than a injector or bad plug.
Good luck as a engine misfire can be a pain to find sometimes.
Curious about the MB code.
This is what I have for M272 engine:
0987 - Ignition coil primary current cylinder 5 (P0355)
0986 - Ignition coil primary current cylinder 4 (P0354)
Your initial problem was posted as P0354.
Could something else be going on? You cleaned the coil connectors with electrical contact cleaner. Does the battery voltage hold steady at 12.6V or more? It’s usually about 13.5V with the engine running.
Have you cleaned the ECU connector? <- First disconnect the battery, and only spray the wiring harness connector.
Can you monitor the fuel trims? That can be diagnostic for a problem with injectors, but it only shows performance by cylinder bank. One leaking injector will cause the ECU to lean out that bank maybe starving the other two cylinders.
I skipped from M112 to M276, so I’m not familiar with M272 idiosyncrasies.
First if you only swapped coils and didn't do spark plugs that is a must since you have only done the coils a spark plug could still be a issue.
After that if you still have a misfire and a code I would then do a fuel injector swap as it's very possible that one could be leaking and causing a rich misfire. Also you can do a compression test of all the cylinders to rule out internal wear or damage.
Weather you do the injector swap or the compression test first would depend on which is easier to do IMO. It's something you should try to fix our it can cause you catalyst too get saturated and need to be replaced which is much more expensive than a injector or bad plug.
Good luck as a engine misfire can be a pain to find sometimes.
The code is specifically for an ignition coil circuit fault on cylinder 4. Would that still potentially be any other issue on it?
Curious about the MB code.
This is what I have for M272 engine:
0987 - Ignition coil primary current cylinder 5 (P0355)
0986 - Ignition coil primary current cylinder 4 (P0354)
Your initial problem was posted as P0354.
Could something else be going on? You cleaned the coil connectors with electrical contact cleaner. Does the battery voltage hold steady at 12.6V or more? It’s usually about 13.5V with the engine running.
Have you cleaned the ECU connector? <- First disconnect the battery, and only spray the wiring harness connector.
Can you monitor the fuel trims? That can be diagnostic for a problem with injectors, but it only shows performance by cylinder bank. One leaking injector will cause the ECU to lean out that bank maybe starving the other two cylinders.
I skipped from M112 to M276, so I’m not familiar with M272 idiosyncrasies.
I haven’t checked the voltage yet but I have a back probing set I can break out somewhere in my tools. I haven’t checked fuel trims yet either but my scanner does let me.
As for the ECU, I did think about trying it a few weeks ago so I disconnected the battery and pulled the plugs off, but they seemed perfectly clean so I decided to hold off to avoid potentially damaging it on accident.
Okay so update. I cleaned the **** out of the ECM and connectors as well as the connector for the ignition coil. I also gave it a shot to swap the spark plugs over too but nothing I did made a difference. The code came back on the scanner right away. I also pulled up live cylinder data for cylinder #4 and drove around and even when it was vibrating like hell and the RPM’s were dancing all over, there wasn’t a single misfire on the cylinder at all.
The voltages all checked out as well, though I have a cheap multimeter and I may go get a nice Klein one to verify those readings.
I’m honestly stumped on this one. It says specifically that there is “a fault going from the ignition coil to the control unit”, but I followed the wires all the way to the ECU and there’s no torn harness jackets or electrical tape or anything like that. I get no other codes at all, and even this code isn’t enough to set off the check engine light. I just have to manually use my scanner to get it to show a code. I’ve got a lot of experience chasing down electrical issues, but I’m really lost on this one. Does anyone have any suggestions at all?
Curious about the MB code.
This is what I have for M272 engine:
0987 - Ignition coil primary current cylinder 5 (P0355)
0986 - Ignition coil primary current cylinder 4 (P0354)
Your initial problem was posted as P0354.
Could something else be going on? You cleaned the coil connectors with electrical contact cleaner. Does the battery voltage hold steady at 12.6V or more? It’s usually about 13.5V with the engine running.
Have you cleaned the ECU connector? <- First disconnect the battery, and only spray the wiring harness connector.
Can you monitor the fuel trims? That can be diagnostic for a problem with injectors, but it only shows performance by cylinder bank. One leaking injector will cause the ECU to lean out that bank maybe starving the other two cylinders.
I skipped from M112 to M276, so I’m not familiar with M272 idiosyncrasies.
I just reread your post and I understand what you were saying about the codes now. I see what you mean that 0987 comes back to a cylinder 5 circuit issue but P0354 comes back to a cylinder 4 circuit issue. That’s very strange and now I’m going to try just swapping the cylinder 5 over as well to see if it makes a difference. That’s very strange.
I just reread your post and I understand what you were saying about the codes now. I see what you mean that 0987 comes back to a cylinder 5 circuit issue but P0354 comes back to a cylinder 4 circuit issue. That’s very strange and now I’m going to try just swapping the cylinder 5 over as well to see if it makes a difference. That’s very strange.
That’s what I’m getting from a thing called Xentry Tips. But it’s not official MB. It could be wrong but it’s never led me astray before??? Since your ECU is not detecting misfires, the electrical discharge characteristics must be normal. Most of MB’s DI engines can detect a cylinder leak like a valve or head gasket problem. Not being completely familiar with M272, I don’t know if it does. Have you done a compression test?
That’s what I’m getting from a thing called Xentry Tips. But it’s not official MB. It could be wrong but it’s never led me astray before??? Since your ECU is not detecting misfires, the electrical discharge characteristics must be normal. Most of MB’s DI engines can detect a cylinder leak like a valve or head gasket problem. Not being completely familiar with M272, I don’t know if it does. Have you done a compression test?
After researching I found the same weird thing with the codes that you did. I tried switching the ignition coil from cylinder 5 with cylinder 1 and no difference either.
I have not done a compression test because I just don’t understand how it would be relevant to the code I’m receiving. I’d have to buy a kit for it but I could always do that if that’s what you guys think is the next step.
After researching I found the same weird thing with the codes that you did. I tried switching the ignition coil from cylinder 5 with cylinder 1 and no difference either.
I have not done a compression test because I just don’t understand how it would be relevant to the code I’m receiving. I’d have to buy a kit for it but I could always do that if that’s what you guys think is the next step.
Nothing is pointing to a resolution, really. I am wondering, but don’t really know, if there is a mechanical problem and the P0354 is just a spurious code. (I have had cars that had them that had absolutely nothing to do with performance or economy). Or is there a problem in either the wiring harness or the CANBUS. Those would be really time consuming to sort out. Or, worst case, is it the ECU itself. For me, the compression test would be an easy and inexpensive way to rule out a mechanical failure. But I have a small shop, I don’t have to buy anything to do it.
Nothing is pointing to a resolution, really. I am wondering, but don’t really know, if there is a mechanical problem and the P0354 is just a spurious code. (I have had cars that had them that had absolutely nothing to do with performance or economy). Or is there a problem in either the wiring harness or the CANBUS. Those would be really time consuming to sort out. Or, worst case, is it the ECU itself. For me, the compression test would be an easy and inexpensive way to rule out a mechanical failure. But I have a small shop, I don’t have to buy anything to do it.
I’ll pick up a compression tester and maybe even a leak down tester sometime this week. Hopefully that’s not the case with me.
I would continuer on with a compression test. Can pick the tool up very cheap. To do it properly you should have all the plugs out and the throttle blades wide open.
If it fails a compression test then move on to a cylinder leak down test. If it passes the compression test there's no real need to do a leak down test.
Then
If it passes swap fuel injectors with one next to the problem cylinder and if the problem remains in the original cylinder then you have eliminated the mechanical end off it then it's time to dig into the electric side of it.
Search for problem components and water damage inside any modules and Thier connectors. Leaving wiring inspection for last as the wiring is usually not a issue butt the result of a failed components
Last edited by RobertR728; Feb 9, 2025 at 04:01 PM.
I would continuer on with a compression test. Can pick the tool up very cheap. To do it properly you should have all the plugs out and the throttle blades wide open.
If it fails a compression test then move on to a cylinder leak down test. If it passes the compression test there's no real need to do a leak down test.
Then
If it passes swap fuel injectors with one next to the problem cylinder and if the problem remains in the original cylinder then you have eliminated the mechanical end off it then it's time to dig into the electric side of it.
Search for problem components and water damage inside any modules and Thier connectors. Leaving wiring inspection for last as the wiring is usually not a issue butt the result of a failed components
How do I pop the throttle blades open? It’s always been my understanding that all you had to do was take out the plug and bleed the system of all its fuel by removing the fuel pump relay. Obviously I was mistaken and I want to do it the right way.
Also, do I have to remove all plugs or just the plug for cylinder 4, since that’s the only real problem cylinder?
Yes you should remove every plug to do a correct compression test.
Remove the air intake tube off these throttle body and prop the blade open with something that will hold it open.
You want all plugs out and fuel off by pulling fuel pump relay or fuse and test and record all cylinders compression.
You want the car to crank the same amount of times for each cylinder if possible. So a battery charger installed on high is a must also. So you have a constant battery charge to crank each cylinder.
If you have a low cylinder when comparing to the other cylinders then spray oil into that cylinder and repeat test only on that cylinder to see if it improved or not after adding oil.
If all cylinders are closer to each other then you most likely have a good mechanical system.
Check the fuel injector if it passes the engine compression test. If fuel injector passes the test also then it gets more complicated because your gonna check for electrical demon's. This can be a long process so cross that bridge if you get there
Ps if you've never prepped open the throttle blades then you have probably never cleaned it either. Hey sooner throttle body cleaner and a tooth brush style soft brush to scrub the circumference of these throttle opening and the front back and edges of the throttle blade. This should be done every 50k or so
Last edited by RobertR728; Feb 9, 2025 at 06:37 PM.
Yes you should remove every plug to do a correct compression test.
Remove the air intake tube off these throttle body and prop the blade open with something that will hold it open.
You want all plugs out and fuel off by pulling fuel pump relay or fuse and test and record all cylinders compression.
You want the car to crank the same amount of times for each cylinder if possible. So a battery charger installed on high is a must also. So you have a constant battery charge to crank each cylinder.
If you have a low cylinder when comparing to the other cylinders then spray oil into that cylinder and repeat test only on that cylinder to see if it improved or not after adding oil.
If all cylinders are closer to each other then you most likely have a good mechanical system.
Check the fuel injector if it passes the engine compression test. If fuel injector passes the test also then it gets more complicated because your gonna check for electrical demon's. This can be a long process so cross that bridge if you get there
Ps if you've never prepped open the throttle blades then you have probably never cleaned it either. Hey sooner throttle body cleaner and a tooth brush style soft brush to scrub the circumference of these throttle opening and the front back and edges of the throttle blade. This should be done every 50k or so
I actually cleaned it very recently, thank you though. I just always propped it open with a gloved hand and cleaned it that way, never stuck anything in there to hold it open and don’t want to cause damage. I will get a compression tester and if they all check out I’ll swap an injector around while the fuel system is drained anyways
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