S65 AMG misfires (not the usual)

alexanderfoti

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Hi all!!

My S65 is playing about. Having fixed the low boost issues I now have full boost (yay) but have issues with misfires.

Specifically, it misfires above 4500rpm full throttle.

So reading the codes, it was 7,8,9,10,11,12.

I replaced all plugs, both packs (reconditioned) and then drove it. This time, the misfires where much worse, junk recon coil packs. Back they went and 2 new MB packs.

Same as before, misfires above 4500rpm on one bank at full throttle.

New ignition controller

Now, I have misfires on only 7 and 12, but, I haven't tested it more than once yet.

The junk packs highlighted something though. With the recon packs, the misfires where violent and easily recognisable. With the new MB packs, and before, I only know the car is misfiring due to the flashing check engine light, otherwise its unnoticeable.

People love guessing on this engine so any ideas?

Some people have said blocked cat on that bank but the car drives absolutely fine up until that point.
(easily tested with a backpressure tester though)

Others have said fuel filter.

Car drives absolutely fine other than this, but testing is a bit difficult, as you can imagine, as full throttle in second is quite fast....
 

LostKiwi

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Reset the adaptations. If it's been driven while poorly they'll be all to cock.
 
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alexanderfoti

alexanderfoti

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alexanderfoti

alexanderfoti

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Just checked them for sanity as I reset them about 400 miles ago. Passenger side bank (one with misfires) is being leaned out slightly 0.981 LTFT vs 1.028 for the other bank. Have done a default initialisation whilst I Was there. Will report back again.

Thinking maybe cam/crank sensor is more likely than blocked cat considering it pulls well up to 4500rpm!
 

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Good a poor tank of fuel cause some of these symptoms ?
 
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alexanderfoti

alexanderfoti

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Its been doing it for a 2000 miles or so..... so unlikely
 

LostKiwi

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Crank sensors tend to work when cold fail when hot. They are unlikely to cause an issue on only 2 cylinders. Same with cam sensors.
This will be something like an injector, lambda (though this would be more random), fuel trims, vacuum leak etc.
 
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alexanderfoti

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Crank sensors tend to work when cold fail when hot. They are unlikely to cause an issue on only 2 cylinders. Same with cam sensors.
This will be something like an injector, lambda (though this would be more random), fuel trims, vacuum leak etc.

So I have done boost testing, the whole inlet holds boost pressure at 25 psi without leaking externally. So all the one way valves, vac system and hoses are all air tight.

I agree, on cam/crank sensor fronts. Nothing makes me think its those sensors but the keyboard warriors over on mbworld are all guessing those.

Keep in mind, up until this point, the misfire codes had been all cylinders on one bank. I need to drive the car again and get it to misfire again (will do tomorrow) to see if it still continues to misfire on those two cylinders, or all cylinders on one bank again.
 

LostKiwi

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Just checked them for sanity as I reset them about 400 miles ago. Passenger side bank (one with misfires) is being leaned out slightly 0.981 LTFT vs 1.028 for the other bank. Have done a default initialisation whilst I Was there. Will report back again.

Thinking maybe cam/crank sensor is more likely than blocked cat considering it pulls well up to 4500rpm!
Those lambda values are out of spec - the target is 1.00 +/- 0.01. Those are a long way off. Was the bank with misfires the one with the lambda of 1.028?
 
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alexanderfoti

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Keep in mind that the car has water/methanol injection that starts at 10psi.

Its had it on for 6000 miles or so. Having the system on or off makes no difference to the misfires but this would likely make my ltft lower than usual.They are still lop sided.

I have new o2 sensors on the way.
 
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alexanderfoti

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On a side note, what are the LTFT limits?

I will probably up the start pressure a bit as the meth shouldnt affect trims ideally
 

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25 psi is quite high. In my turbo experience many years ago, I had to reduce plug gaps quite a bit to ensure they fired when using high boost. Bit hard with modern plugs I know. I was using single electrode which were easy. Just a thought though as it does seem the issue is with ignition.

Ian.
 
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alexanderfoti

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25 psi is quite high. In my turbo experience many years ago, I had to reduce plug gaps quite a bit to ensure they fired when using high boost. Bit hard with modern plugs I know. I was using single electrode which were easy. Just a thought though as it does seem the issue is with ignition.

Ian.
Thanks Ian.

Yes, it's actually closer to 23psi.

You are right with the plug gaps, these cars are sensitive to the right plugs but these are the correct ones with 0.7mm plug gap.

To me, it feels like a soft misfire, rather than a hard one caused by worn plugs etc.
 
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alexanderfoti

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Can you swap the coils from one bank to the other to see if it changes the plugs that are misfiring? Might be a pointer.

Ian.

No, they are sided (thanks MB), although the whole ignition system is new. and the old coils and the new coils had the same behaviour so I don't think its ignition related.
 

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Normal Lambda limits should be 1 +/- 0.01 so I would expect 0.99 to 1.01
 
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alexanderfoti

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Normal Lambda limits should be 1 +/- 0.01 so I would expect 0.99 to 1.01

but the adaption limits are further, I think 0.950 and 1.050 respectively?
 

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Just a thought Alex and as you say we all love to guess on this engine but I’m not very familiar with it- hence my question is basic so I apologise in advance - are your ignition coils installed directly on the spark plugs?
 

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watching wid great interest here .bon chance
 
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alexanderfoti

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Just a thought Alex and as you say we all love to guess on this engine but I’m not very familiar with it- hence my question is basic so I apologise in advance - are your ignition coils installed directly on the spark plugs?
I welcome out of the box guesses. It was more aimed toward the ones over on MB world that say:

Oh yes, its this XXXX expensive part, oh not that? then its this xxxx expensive part.

The coil packs are all one unit and are coil on plug type, with no wires.
 

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