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2000 CLK 320
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Discussion Starter #1
Cylinder misfire on #4. Possible causes are spark plugs (just replaced 6 months ago) ignition coils/coil pack. vacuum leak, injector fault, high or low fuel pressure.

I was driving behind some jerk and I needed to quickly get away from him. So I gunned it. (kickdown and eveything) to pass him. All of a sudden check engine light comes on. and I get this code. Idle is crap, the car runs very bad. I barely make it home and shut car off. Then, I restart it and the light is still on, but the car drives fine? What could this of been? a gliche? I'm thinkiing maybe a bad reading on either the coil pack or wires. What are they supposed to be reading? Any help is greatly apreciated guys. Oh, and FYI I will be doing front lower ball joints DIY in the next coming weeks.
 

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Discussion Starter #3
Thanks Keyhole. I dont think it would be a leaking head gasket or an injector. I think what it is, is a bad wire or coil. Do you know what they are suppose to measure when reading them from a multimeter? And its weird it happened as soon as I floored it. What would cause it to do it then? its so weird??!!?? and now it drives fine and the checkk engine light is still on? Im so stumped on this one.
 

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When it starts running badly like that (you left out that the CEL started flashing, didn't you?) it means the ECU has shut down one or more cylinders. All you need to do is pull over and shut it off, then restart and the ECU will reset. Not a glitch, but working exactly as designed.

In your initial list you left out the ignition wires. That was my issue, but while I kept pulling a P0303 code, the bad wire was actually on cylinder 4.

When you changed the plugs, were you careful to plug the wires back in properly? The plugs fire sequentially, so it's important to be sure that the a coil output goes to the a cylinder, b to b and so on for each cylinder. Also, did you use the boot tool? They can be damaged if they are manhandled.

The easiest thing to do is swap the coils on #4 and #5 (be sure not to overtighten the fastener, that can cause misfires too). Don't swap the wires, just the coils. As you do that you can verify the wires are plugged in properly. Then reset codes and go for a drive. If the miss moves to the other cylinder, it's the coil. If not, then test the wires. Nominal is 22K, replace anything 26K or higher. You can buy them individually, they are expensive.
 

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Discussion Starter #5
My CEL didnt flash, it just popped on when I gave it huge amounts of gas tryin to pass someone. It just stays on non-stop now. Im going to use a multimeter tomorrow morning and see what results I can come up with. Im also going to swap out the coils and see if the code pops up with the new coil on the new cylinder. These cars so are difficult to understand at times. It's like you have to have a Masters in W208 :)
 

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My CEL didnt flash, it just popped on when I gave it huge amounts of gas tryin to pass someone. It just stays on non-stop now. Im going to use a multimeter tomorrow morning and see what results I can come up with. Im also going to swap out the coils and see if the code pops up with the new coil on the new cylinder. These cars so are difficult to understand at times. It's like you have to have a Masters in W208 :)
Be sure you clear the codes after you swap the coils, and check to see if they are cleared before you start the car again.

Other than confirming a-a and b-b for the wires I wouldn't bother testing them for resistance right now. It's extra work, and you can damage them by playing with them too much. Just swap the coils, clear the codes and see what happens.

Good luck.
 

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Discussion Starter #7
I didnt have the wire tool to get the wires out. Just a pair of needle nose pliers. I didnt damage anything, it was all working fine except for tonight. I blame it all on the A$$ that was driving dangerously close to me. I wouldnt have had to show him the power of the Mercedes if he was driving normally. And then, none of this would of happened. I think what happened is maybe a fuel injector didnt supply enough gas to the chamber and that sparked the CEL, but now it seems to run fine, I dont get it

If its running fine now, why would my CEL light still be on? My buddy has a OBDII, I'm going over his house tomrrow and have him reset my codes. If it comes back, then, I know I have something to worry about. I think it was just a glitch. Maybe I'm wrong. Ill let you guys know the results tomorrow.
 

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The OBDII system stores codes from various malfunctions. When they are serious enough or enough of a certain kind accumulate, the light goes on. It's based on an algorithm. Once enough drive cycles have been completed without the code being triggered again, the system will turn the light out automatically.

It's possible you had a pending code for P0304 long before this occurred, but it wasn't significant enough to trigger a CEL before now.

You can surmise any number of things for the cause, but whatever triggered you to throttle it was just a matter of time. That's actually your test, do a rolling start and then hard accelerate in a place not known for cops where it is otherwise safe to do so. My guess is you'll have a recurrence until you find and repair the actual issue.
 

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Discussion Starter #9
Thats a good idea Greg. I will do a normal take off, and then floor it. I'll see what happenes. If it only happens when I floor it, that means its probably a fuel injector. But, I think you are right. It did shut off cylinder #4 when the CEL came on. It just didnt flash. Steady CEL. I shut off and restart, car drives fine now. Still light on.
 
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