Just bought a used S65 AMG and after 800 miles of driving away from the guys house I get a check engine light after I floor it and the car starts running poorly and vibrating. I turn off engine and start back up and it runs fine. I take it to Mechanic and it is a Cylinder 5 and 6 misfire and they say spark plugs possibly ignition coil. They take 2 spark plugs out for Cylinder 6 and they are coated in oil. Mechanic says $10 to $12K for a valve job. Bore scope shows that the valves are full of oil. I drove to Car Max and they offered me $16K less than I paid. I know it immediately needs brakes and spark plugs still need replacing because I am at 65K miles. Do I sell and take a bath or do I hold onto this PIECE OF S#%T! I am so mad. It sounds like a valve job is a massive undertaking and that they can get it all back together again and fifteen days later I have new problems. So confused - any info is appreciated. It only comes on when I floor it - when I drive lightly there is no issue at all!

 

Don't panic. Don't believe everything everyone says. If it idles and runs smoothly when you drive gently, it makes it less likely there's serious problem.

The first thing will be to change all the spark plugs. Not a trivial job - lots of ways to get it wrong.

After that you would need to look at the ignition coil packs, which are more expensive, but an all-too-common failure.

Nick

 

It is not the ignition coil or the spark plugs - neither of those would place large amounts of oil in the cylinder. There is something wrong with the valves as they are not sealing properly. The #6 cylinder has 180 psi and the #5 has 192 psi. If the valves are full of oil it has nothing to do with the ignition coil or the spark plugs!

 

Indeed. Do a valve job then.

 

Both compression readings are within 10% variance.....it may be just valve stem seals which "should" be able to be done without removing the heads.....take it to another shop for a second opinion......I'm also not sure when you say "valves are full of oil"....if you mean theres oil in the cylinders then its either rings or likely valve stem seals.....compression test eliminates rings sooo......

 

Valve seals shouldn't throw a CEL. On a 55 motor the crankcase breather can put gobs of oil in at random. Not familiar with the 65 (yet), but ignition problems are common, and will throw a CEL. Is the car smart enough to stop fueling a cylinder with no spark, thereby not rinsing oil? Valve seals usually wear and age evenly, so it should smoke a lot until the cats warm up if they are bad. My money is on ignition problems from the info so far. It is also much easier to fix.

 

These responses are great. I ditched the South Bay Mercedes dealership and found a really great hands on mechanic and he agrees with StarvingArtists assessment - sort of. He feels that there is no way that the vehicle just passed smog check 2 months ago and then all of a sudden has valves that are failing at 65K. He is starting with a treatment of the 91 octane gas to see if he can blow out the fuel injectors. He has been seeing that there is unburned gasoline coming out of the exhaust pipe from Cylinders 1-6 but there is not unburned gasoline coming out of Cylinders 7-12. The dealer changed the #6 cylinders spark plugs five days ago and they are already junked up but it is not clear if it is from oil or from wax buildup yet. He had the computer hooked up to it while I was there and the car was at idle for a while. The misfires would completely go away and then five minutes later you would see a few in 6 and then 7 and then go away and then come back in a wave and then go away for 5 minutes or so. He said if it was the valves seating he doesn't believe it would come out of nowhere and then just disappear. He said the engine wants 98 octane gas with a minimum of 93 *which is absurd as the best gas you can get is 91 but with this level engine a fill up at Costco's 91 octane will kill the injectors. Maybe it is the ignition coil which would really **** me off in that is all I wanted the South Bay Mercedes to change but they said there is no way that that would cause the oil residual (or whatever it is) in the cylinder....but StarvingArtist asks a great question - if every time there is a misfire the unburned gas is mixing with the carbon is that causing the gunk immediately - THERE IS NO SMOKE- NONE - but it is going thru oil and the misfires are causing it to run thru gas quickly as well. A crummy valve spring was my guess??

 

Bad ignition coil/s will cause issues with plugs fouling and raw gas out the tailpipe.....it can also ruin cats and wash the cylinders causing compression problems. You may get lucky and it may just be bad coils. I'm not familiar with your model but does it have a PCV or oil separation system? Maybe thats defective? Not sure why the dealer would just change the plugs and not investigate why they fouled in the first place?

Btw, I doubt its a bad valve spring. Get a wet compression test done along with leak down to eliminate rings then go from there.....

 

+1 on the PCV system for the oil, and I would stop running it until you get the ignition fixed. There is a lot of info here and on the CL SL forums about the coil packs and I think it's called the controller. An hour with the search feature and you will know more about it than your mechanic.

 

The dealer was certain it was a $10,000 valve job. He said that if you just bought it I would immediately sell it as these V12s are horrible. To be fair everyone says that but that is besides the point - I absolutely love its look and drive as a 6'6" guy and I will lose my shirt. I brought it in to do the coil and they stopped because they said there is no way a coil would cause the mess in the spark plug?! I will ask the mechanic about the PCV and the controller is something he brought up - that I have a bad controller for the ignition. The new mechanic is like you guys - passionate and like a good doctor is looking at this like a puzzle to be solved. I am going to be so sad if it really is a valve job though and all this time and effort has been for naught and the dealer was correct......and I will have a ton of $$$$$ out the door! Again - thanks all for your input!

 

Another thought......if the oil seals in a turbo go bad she will also eat oil through the intake side....

 

You would see oil smoke from the exhaust. Been there; long horrible story.

Have to admit I can't explain the oily valve with anything other than a bad valve seal, but that still doesn't fit the misfire on WOT symptom. Sounds like two problems.

Nick

 

My bet is the coil is the misfire issue, period. My car runs fine on 90 octane so it's not the 91 the OP is running. The CL's ECU will adapt just fine. My car also has oil residue on #6 plugs, and I'll bet if I went in with a bore scope I'd see it on the vales as well based on how the plugs looked when I changed them at less than 50,000 miles. However, a bad coil will misfire under load. I'd say replace the coil, and put new plugs in cylinder #6 every 25-50k miles and enjoy the car. I DD mine year round in Alaska and by Monday will have made over 150 passes down the drag strip with my car (over 130 already), and did I mention mine also has oily plugs in cyl#6?

Mine does misfire occasionally too, but only after a weekend at the track running 109 fuel, then refilling with 90. The first time or two I go WOT it will misfire, go into limp until I shut it off and restart, then it's fine again. That's the only tuning I do to swap fuels, a couple restarts. But even that may be a thing of the past with my new tune from Eurocharged.

 

I have now been to two separate mechanics since the Dealer told me that I needed a valve job. Neither of the two mechanics believe the dealer - they both laughed. So I took the ride out to Palm Desert from LA and it was running like a champ. I have been putting a German additive Liqui Moly Fuel Injector cleaner in and I was driving it easy then harder then harder and finally tested it and pushed it hard as I was going about 90 miles an hour and it took me up to 110 and then the misfire happened again. I pulled over immediately and turned the car off and then fired it up again and it ran fine again.

I tender footed it around town for the week and then tender footed it home but still got it up to 100mph without any issues but we all know the car does that in under 3000 rpm as you take it thru the gears. I put some 100 octane racing gas in it but only the last 10 gallons as the stuff costs $10 a gallon. I am scared to death of pushing it hard and that is a car that nobody wants to have.

Dr. Matt- what you are telling me is exactly what the first mechanic I saw told me and he is the one that said change the coil. So instead of taking it to him I took it to the South Bay Mercedes dealer and they said NO it couldn't be the coil and they changed the spark plugs and said it needed a valve job. I am going to be LIVID if I took it to them for the coil replacement and then didn't do what I took it to them to have done and they misdiagnosed it. I think the higher octane and additive are helping but everyone that hears that it never did this before and then after flooring the car really hard a few times (ten) I started getting this misfire.

The coil is going to cost me $2100 and I would do new plugs on all 6 cylinders. I do not want to just throw that down the toilet and find out that it isn't the coil. What blows me away is that based on what Dr Matt is saying that they wouldn't have just done what I told them to do in the first place!

So aggravating!! And what is Eurocharged (that sounds expensive but cool!)

 

There is no fool-proof, concrete, trouble-shooting with these things. You use the best clues and information that you can get, and make the best judgement you can at each stage of the process.

One method is to start with the simple and inexpensive fixes, and cross your fingers. You might fix it quickly and cheaply or you might not.

As you eliminate the possible causes, you re-evaluate what each piece of information is saying at each stage.

If you need to spend more money, do it when you need to and not before. Don't start with the most expensive solution (the valve job) as that's just as unlikely to solve the misfire as new spark plugs, and you may spend lots of money without fixing it.

There are two other things to consider. One is what are the common faults on these cars, and everyone on MBW will all chorus with same answers: coil packs, EIS, CPS, IC pump, engine mounts, conductor plate, tranny connector, heater drains, and especially ABC. So if your car has any faults, its quite likely to be one of those. The oily bits rarely cause problems.

The second is that looking after a W220 is difficult - too difficult even for most professionals, so you need to be very sceptical about what people tell you. In general, they just want your money. There ARE some good mechanics around, but they tend to be specialists, rather than general mechanics. Alternatively, you could listen to the opinions of some very experienced enthusiasts who will give you very good, unbiased advice for free.

Nick

 

Nick,
I get it and agree. I am a home builder and I use the same concepts a lot of the time. I just came from the mechanic and he said that I had a misfire in 5, 6 and 7. He still firmly believes that it is the fuel injectors in that the previous owner had a bad fuel pump and he was having misfires in all of the cylinders except 6 and he firmly believes that the fuel pump on this car would not have gone bad at 58K miles. Low fuel pressure was causing the codes and they replaced the fuel pump and then at 60k the shutoff valve and the purge valves were replaced. He is saying that it doesn't make sense that the misfiring cylinder is bouncing around and that it is very commonly 6 but that not always. He believes that the fuel pump has the filter in it and that over the years that crap has built up in the fuel injectors and that when I step hard on the gas the flood of gas that should mist out of the injection system is coming out as a spray and that it only happens when I step hard on it. When we had it at 2 to 3K RPMS and at idle you get no misfires at all. When it just idles normally you barely get any misfires and the only time it really misfires is when you go over 3500 RPM. He say it will cost me nothing to baby the car for another month and go thru 3 or 4 tanks and see where I end up after that. He says it is going to take time to clean out the injectors if that is really the cause of the misfire and that it will not happen overnight.

In the end I agree with you Nick and I am doing just that....trusting the mechanic I like the most *(not the dealer!) and will take it one day at a time. I just want to be able to floor the thing sometime soon and not have it misfire!! If not the car is worthless to me. My Infiniti M45 and my ML 550 both scream compared to this thing - even my Chevy Suburban would smoke the S65 at this stage!

 

On a cls55 and many other models, you are supposed to change the fuel pump at 60k as maintenance. The injector theory makes sense, but for some reason I don't buy it. I suppose it's not easy to just pull one and bench test it. I'm still betting on ignition.

 

Im with Artist on this one.....

 

You're just muddying the water with the oil thing. It would take an EXTREME amount of oil consumption to cause a misfire. I'm in the used car business. I've dealt with numerous vehicles burning a quart a week that didn't even foul plugs to the point of causing any misfires. You would be putting a ton of smoke out the tailpipe before it would cause a misfire if it was due to oil consumption. Likewise, oil on the valves from valve stem seals would not cause a compression issue (if anything, it would raise the comression test numbers due to being a "wet" test) so I'm not sure why they would be trying to tie those two things together.

180 compression is fine. Most engines won't start misfiring until they are under 100. You most likely just have the same ignition issues we all deal with...coil/spark plug/voltage converter issues.

 

OP pattern failures are in most cases very helpful.

I consistently see misfires in the tt-12 get diagnosed as (fill in the blank with stupid $$$ figure) that end up fixed with fresh spark plugs and a coil pack.

Fuel injectors? We got to replace those all the time when we first got 'Oxygenated Gasoline' that also saw to it that every carbureted car on the road got a carburator rebuild. Current injectors (2000 or so and newer) are much better and rarely have issues by comparison.

Don't diagnose by WAG.

When you hear hoofbeats... Think horse... Not Zebra.

 

I'm waiting to see the conclusion to this.

 

I'm still sticking with ignition issues....

 

Don't panic. I don't think you have an issue with engine. I suspect that you have an ignition issue and that the oil on the plug is unrelated to your misfire.

To echo Dr. Matt, I also have slight oil deposit on back cylinder. In my case I have it in cylinder 12. I ran compression test, leakdown test and all was good. I had intake manifold off and there was no significant oil deposit on valves. I replaced the valve seals thinking that was the issue and changed the plugs. However, I recently had the plugs out again, and there is slight oil deposit on plug. In my case, it is not causing any misfire or check engine.


As for the misfire issue, this is likely ignition coil or the voltage transformer. A good mechanic with proper tools should be able to check.

As for the oil on the valves, obviously want to have all the tests done. Compression, leakdown, etc. If those check out, then look to inside of the valves, the stems. If the stems are wet then valve seals. But again. in my case this didn't solve my issue so ))

PCV or crankcase ventilation can also be an issue. one major thing to check on our engines is teh PCV system. I changed mine and the valve at the front of the drivers side cylinder head was completely shot. The diaphram inside rock hard. The design of the PCV allows PCV suction when at idle and at idle bypasses the intake system, going straight into the intake manifold. Also if the system is stuck the other way, excess crankcase pressure will build up to very high levels with no where to go.

 

The OP seems to have disappeared.

 

UPDATE - per earlier posts my mechanic assured me that it was a clogged fuel injector because only cylinder 6 was misfiring and it only did it at high RPM. SO - I drove it out to the P. Desert and back and around town and threw another 2k miles on it without going over 4,000 rpm quickly as this beast can easily go over 100mph without going over 4k rpm as long as it climbs slowly. I had the misfire once or twice and I just restarted and it was fine - SO today I take it out for an hour and back for an hour (150m roundtrip) and it is great. I shut it off and then run into store and when I come back out it misfires except unlike the other times I can not shut it off and back on to correct the issue. It is cylinders 2,4,6 and at times 5 and 7. I drove it in limp mode to mechanic with 67,500 miles and he says this time he wants to change all spark plugs and low and behold ignition coil on passenger side. I said that is why I originally took it to the dealer and then him and blew $1K doing so. He said when it was consistently only one valve misfiring it was one thing. He said I got the engine really hot on the drive and now that I have all these misfires he is more prone to believe that its spark plugs and ignition coil?! I said if you replace one bank I want both banks or all 24 plugs pulled and the passenger ignition coil changed. I pray this is it!