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'06 CLS500 '01 CLK320, '84 300D
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Discussion Starter #1
My CEL light is on, and it has been throwing code P0305 for a couple months now. I have replaced the plugs on that cylinder, changed wires, swapped the coils around, and just recently re-installed my injectors after I had them cleaned and flow tested, same result (even after clearing the codes)

Symptoms of the misfire are: rough idle, and off-key shifting: sometimes she almost redlines off the line before shifting into 3rd (when i am hard on the accelerator off the line).

Any idea on where I look next???? I'm about to break down and bring her to the stealership :-\

Thanks in advance
 

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'01-E320 & 02-ST2
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Just a couple of thoughts.

Did you swap injectors when you put them back on or did you put them back in the same place?

Did you do a compression check?

Have you removed the plugs to see how they look in comparison with a neighboring cylinder?

There is also an injector repair kit available for the connector, which leads me to believe those can be problematic. It's under $8 at autohausaz.com so that's probably worth a shot before you have it das-ed.

Take care and enjoy the ride,
Greg
 

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C230K Sport Sedan
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Most of the time these single cylinder misfires are fuel related (weak or dirty injector or FI connector).

But it could certainly be a head gasket issue or dirty exhaust valve that's leaking. So definately have a compression and leak down test performed to isolate the problem. What they do on a leak down test is replace the sparkplug with a a compressed air fitting and fill the compression chamber with air pressure and see if it holds. If it doesn't hold, say it goes down to 100 PSI, then the air leaking has to go somewhere, right? So you listen for the hiss of air escaping. For example, if it's coming out the tailpipe, it's a bad exhuast valve, if it's comming out the dipstick tube, it's rings and so on.
 

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It sounds to me as the classic clk MAF problem...misfires..rough idle..shifts wrong...hesitation. Do a search on both MB forums for MAF problems and see if it sounds like your issue. It does not always throw codes but the symptoms are there. The MAF and CPS are the #1 and #2 issues w/CLK. I can't remember injector issues ever being mentioned on the forums.
 

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'06 CLS500 '01 CLK320, '84 300D
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Discussion Starter #6
Greg- Yes I swapped them. Injectors are good, when I sent them out they checked every aspect of them, including pulsing, voltage, and flow tests. I have not yet done a compression test (I am actually scared to do so), and I have not redone the connectors (although I am about to order the part). The plugs were pretty fouled, but I only replaced the ones on the #5 cylinder. I would think that plugs being bad on another cylinder would not throw a code for #5 (although I have code P0300 pending, so who knows?)

dl- I was thinking the same (with the symptoms) but I dont believe those throw codes.

Buell- BITE YOUR TOUNGE! I don't want to hear anything about the head gasket.... hope it doesn't come to that. My brother suggested the leak down test... I might have to bite the bullet and have this done.

Tom- first thing I did with all of this was clean the MAF. Nothing changed. I already had MAF issues a while back and replaced it once (about 80K ago), so who knows maybe its time again. I wish I knew someone around here with a 320 motor to swap our MAF's real quick to see if it helps.


I'm $200 deep into this already, between having the injectors cleaned, 2 plugs, and the 2 wires I BROKE when I was swapping those around.... I should have just brought it to the stealership in the first place (they charge $200 to diagnose)

Thanks for the replies!
 

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2014 CLS550 4Matic
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It sounds to me as the classic clk MAF problem...misfires..rough idle..shifts wrong...hesitation. Do a search on both MB forums for MAF problems and see if it sounds like your issue. It does not always throw codes but the symptoms are there. The MAF and CPS are the #1 and #2 issues w/CLK. I can't remember injector issues ever being mentioned on the forums.

+ 50
 

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'01-E320 & 02-ST2
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Greg- Yes I swapped them. Injectors are good, when I sent them out they checked every aspect of them, including pulsing, voltage, and flow tests. I have not yet done a compression test (I am actually scared to do so), and I have not redone the connectors (although I am about to order the part). The plugs were pretty fouled, but I only replaced the ones on the #5 cylinder. I would think that plugs being bad on another cylinder would not throw a code for #5 (although I have code P0300 pending, so who knows?)

dl- I was thinking the same (with the symptoms) but I dont believe those throw codes.

Buell- BITE YOUR TOUNGE! I don't want to hear anything about the head gasket.... hope it doesn't come to that. My brother suggested the leak down test... I might have to bite the bullet and have this done.

Tom- first thing I did with all of this was clean the MAF. Nothing changed. I already had MAF issues a while back and replaced it once (about 80K ago), so who knows maybe its time again. I wish I knew someone around here with a 320 motor to swap our MAF's real quick to see if it helps.


I'm $200 deep into this already, between having the injectors cleaned, 2 plugs, and the 2 wires I BROKE when I was swapping those around.... I should have just brought it to the stealership in the first place (they charge $200 to diagnose)

Thanks for the replies!
While some of the symptoms do suggest a MAF, a bad misfire in a cylinder will do all of that as well and if you've got plugs that look that bad in the cylinder that is a bad misfire (and a really bad misfire in one cylinder can set a code for multiple misfires, that's the 0300). Plus I've yet to hear of a bad MAF that didn't trigger at least ONE of the common MAF codes. Nevertheless, if you want a quick and free check for the MAF, you don't need to swap one, just unplug the thing. It will throw a code and a CEL but it should run okay. I'm guessing you'll still see the same other symptoms, but if not...

I'm guessing you've changed the fuel filter as well? Unlikely that would trigger a misfire code on a single cylinder but if you're over 60K it's due anyway.

The scariest part of the compression check is removing a plug from each of the cylinders. Not a lot of clearance and you have to treat those wires very, very gingerly (as you've discovered). Look on the bright side, pull six plugs, disable ignition, crank crank crank per cylinder and you then have an answer. Don't worry about the head gasket either, the 112 so far has been bulletproof in that regard, so unless you've been running it low on coolant or otherwise abusing it that shouldn't be a problem.

Take care and enjoy the ride,
Greg
 

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Discussion Starter #9
While some of the symptoms do suggest a MAF, a bad misfire in a cylinder will do all of that as well and if you've got plugs that look that bad in the cylinder that is a bad misfire (and a really bad misfire in one cylinder can set a code for multiple misfires, that's the 0300). Plus I've yet to hear of a bad MAF that didn't trigger at least ONE of the common MAF codes. Nevertheless, if you want a quick and free check for the MAF, you don't need to swap one, just unplug the thing. It will throw a code and a CEL but it should run okay. I'm guessing you'll still see the same other symptoms, but if not...

I'm guessing you've changed the fuel filter as well? Unlikely that would trigger a misfire code on a single cylinder but if you're over 60K it's due anyway.

The scariest part of the compression check is removing a plug from each of the cylinders. Not a lot of clearance and you have to treat those wires very, very gingerly (as you've discovered). Look on the bright side, pull six plugs, disable ignition, crank crank crank per cylinder and you then have an answer. Don't worry about the head gasket either, the 112 so far has been bulletproof in that regard, so unless you've been running it low on coolant or otherwise abusing it that shouldn't be a problem.

Take care and enjoy the ride,
Greg

I swapped the MAF with a friend of mine that has a W203 (same MAF), reset the code... no change. Drove with the other MAF for 40 miles, same result. Obviously not the MAF sensor.

Now that I think of it, I haven't changed the fuel filter in quite some time. It's also time to do ALL of the plugs, not just the ones on the misfiring cylinder. The plugs are WAY overdue, and I still have the "pending" P0300 code. That would be interesting if that was the culprit.

I am thinking of ordering the Denso Iridiums unless you guys suggest something else.

Guess I'll be doing those 2 things before I take to the stealership...
 

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clk 320
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ok,here is what you need to do ;take the valve cover and chek the roler on the rocker + the camshaft hump on this cylinder for damage .let us know pleace,i had exacly the same problem week a goo
 
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