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Registered 2004 SLK32 AMG
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12 Posts
Discussion Starter #1
SLK'ers: Anyone out there have this problem. My SLK32 did not pass inspection (which here in New York State is every year). Trouble code P0305 [Cylinder 5 Misfire] coming up on my code reader (see photo). First time. Car not driven all that much -- weekend driving basically. 5,200 miles right now. Original spark plugs and spark plugs wires (2004).

1st plan of action: Check with a spark plug tester if there is a spark at cylinder 5. Pull spark plug on cylinder 5 to see if it is fouled up. If fouled spark plug, wire brush (taking care not to change gap) to see if code goes away. Swap 2 coils to see if problem is due to the coil. If coil is the problem, change the coil. If coil is good, change spark plug ($4-8). As a last resort, do a compression test. Do not see any type of leakage around the engine block. If compression test fails (reading 30 or so), then take it to Dealer $$$$$ ? That's a maybe on the last step.

Any ideas? Past experiences? Solutions? Troubleshooting methods? Anyone had similar issue and resolved it a different way?
Thanks.
P0305-Cyl5MisfireTroubleCodeRED.jpeg
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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98,227 Posts
i had a 304 and it was my cps crankshaft position sensor. That is all I am saying
 

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Registered 2004 SLK32 AMG
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12 Posts
Discussion Starter #3
Thanks Jeff, that's another possibility.
I am assuming you swapped out the position sensor to fix the problem.
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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98,227 Posts
304 was cyclinder 4 misfire but not the code for cps replacement
Yes and all was good.
My tech could not figure it out
he swapped as an example:
ignition wire from 4 to 1
sparkplug from 4 to 2
injector from 4 to 5
coil from 4 to 3

and code came back

then he researched it and my car had 100k on it so he put in a new cps and going on 3.5 years now :D
 

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Premium Member 2002 R170 SLK V8 5.0
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3,171 Posts
You should definitely NOT wire brush Plugs, it just scrapes off the microscopic thickness of precious metal plating on the electrodes.

There are 2 Plugs fired by 2 separate (within same casing) Coils, per cylinder, so 12 plugs in all.

Don't use cheap plugs, use NGK or Bosch.

First thing I would do is change plugs, irrespective of mileage, they are Old ;)

If that don't cure it swap the Ignition Leads with another Cylinder that has the same length leads, (denoted by alpahbetical markings), if the misfire doesn't migrate, then swap the Coil for any of the others ......................................................

HTH,
 

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Registered 2004 SLK32 AMG
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12 Posts
Discussion Starter #6
Hey Dave: Great ideas. Yes, the wire brushing was meant as light brushing of the plug but nowhere near the electrodes. Will try out what you are suggesting. I was thinking in the same way -- changing the plugs with a NGK set. You're right. Will do that anyway! But I want to troubleshoot first to know what caused this problem -- good to know for the future. Yes, I saw that there's a double plug - double coil setup. No Service manual yet. But am working on that. So no cylinder diagram, except what I found on the web.

On the cylinder diagram: what I have is 1-2-3 on the right side (passenger) with 1 towards the front AND 4-5-6 on the left side (driver) with cyl 4 towards the front. Correct? Will try to confirm that with some other info sources.

Also am thinking that since it is running rough (some skips, pulsating at stops,...), it may also be a fuel-air problem, like a dirty or partially clogged injector. Any thoughts?

Thanks.
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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98,227 Posts
6 cylinder numbers

 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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98,227 Posts
ty looking for me? @jbanks15 :D

you had jeff with @ not me :D
 

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Premium Member 2002 R170 SLK V8 5.0
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3,171 Posts
1-2-3 on the right side (passenger) with 1 towards the front AND 4-5-6 on the left side
Yup ;)

Trouble is with a problem like this it could be 101 issues causing it, which honestly is why I use SDS all the time and recommend it, even at DIY level it will pay for itself on a fault like this by eliminating the need to swap expensive parts on trial and error basis, Parts darts as I call it ;)

Without SDS I'd be looking at cheap stuff first, the Plugs yeah that will do no harm, they are old now anyways.

Why not take 1 outta each Cylinder first and then do a Compression test at the same time, shouldn't be an issue, but then you have eliminated that.

My gut says it could be an Air leak, Vacuum and Breather pipes all suffer with age, becoming hard and brittle ;)

HTH,
 

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Registered 2004 SLK32 AMG
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12 Posts
Discussion Starter #12
Yup ;)

Trouble is with a problem like this it could be 101 issues causing it, which honestly is why I use SDS all the time and recommend it, even at DIY level it will pay for itself on a fault like this by eliminating the need to swap expensive parts on trial and error basis, Parts darts as I call it ;)

Without SDS I'd be looking at cheap stuff first, the Plugs yeah that will do no harm, they are old now anyways.

Why not take 1 outta each Cylinder first and then do a Compression test at the same time, shouldn't be an issue, but then you have eliminated that.

My gut says it could be an Air leak, Vacuum and Breather pipes all suffer with age, becoming hard and brittle ;)

HTH,
Hey Dave: Lots of good suggestions. Appreciate it.
Yes, I agree. Will also try to do a compression test on each cyl. Don't have a compression test kit, so will try to borrow one first. Started to remove some of the air intake components, got most of them out. Had to deal with those "special" MB band clamps. But Isaias started hitting NY with rain by late afternoon, so had to stop the effort for now.

Also my spark plug tester is for NON-recessed plugs (about $2 at HF). So may have to borrow or find a tester for recessed plugs -- if that's what's down there. But got down to the wire boots and coil packs when rains started (off and on). Trying to batten down the hatches.

Jeff (jbanks15): Yes, that "at"Jeff was at you. But will use your real "jbanks15" in the future -- not to confuse everybody.

Yes, I agree, this problem could be from lots of different sources. Checking spark, plug, coil is just less costly and can be eliminated more easily, IMO. But injectors, air leaks, vacuum lines, etc are possible. Still have almost a month before my inspection expires.

Can you explain what you mean by SDS? Not sure what that is. When you have time. No hurry.

Break out those candles OR make sure that the generator works.
Stay safe and dry, ALL.
 

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Premium Member 2002 R170 SLK V8 5.0
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3,171 Posts
SDS = Star Diagnostic System, which is the Dealer Level Kit, note that absolutely no other Machine will do all the things you will need to do on an R170, no matter what others say, including the manufacturers of the likes of iCs and "hop sing lotus flower OBD yak yak yak" etc !!

SDS is widely covered on the Forum.

IDK what equipment you have, but you don't want to be using "on car" Spark Plug Testers on these Ignition Systems for a variety of different reasons, one of them being per Ignition Cycle they apply several Sparks to each Plug and not at exactly the same time on each Plug in that same Cylinder, unlike a conventional system which would just Spark once at a pre determined time.

I hope that storm passes without too much destruction ;)

HTH,
 

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Registered 2003 SLK32 AMG
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110 Posts
I had the miss fire code on two cylinders, It came on only at high boost. It would then go into limp mode. It was due to two injectors that were dirty on the face. As it required removing the fuel rail, I did over kill. With 60K miles, I replaced all injectors, coils, plugs & plug wires. I'm quite lazy and did not want to do this again. I had been purchasing the items over the past few years, when I found good prices.
 
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