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Surely MAF would affect more than one Cylinder ?
 

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1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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Yes it does. Check out the pics with the misfire data. When there are multiple misfires, they're consistently on bank 1. 1-6 have higher misfire data compared to 7-12.

Plus these V12's are so stupid sensitive that its hard to tell. It would be significantly nicer (and easier) if this engine was split into four banks, with four of everything....but then the prices would quadruple. Good thing MB didn't do it that way.
 

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2006 S600
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The V12TT uses MAP, not MAF, sensors.

The most important one is on the intake manifold, and reads MAP for ALL cylinders.

I think OP calls this the post throttle MAP.

Nick
 

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2003 S430
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Extremely unlikely in this case (providing the car has the correct oil, changed as required), but one cause for occasional idle misfire is a sticking intake valve. I'm not an expert, but I don't remember ever hearing of a sticking valve on a newer Mercedes.

I agree that a small air leak very close to cylinder four seems to be a possible cause. Doesn't the computer sense misfires by measuring the voltage of the discharge tail thru the plugs? If so, wouldn't that make a lean mix in that cylinder the most likely cause for the error code?
 

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2005 S600
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At your car's age, the injectors themselves are also suspect. A sticking injector that doesn't pulse long enough can cause a lean misfire...

IF you determine that you need to address the injectors, then I recommend this guy:

For a fraction of what new injectors cost (and you've got 12), Paul will clean, rebuild, flow test and balance your injectors. He's done injectors on two of my Volvos and the results are impressive.

Even a few % difference in flow causes a bit of flutter at idle, and less power overall as some cylinders are a bit lean and some a bit rich (the fuel trim is based on O2 sensor readings, and applied across all injectors evenly.)
 

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Discussion Starter #46 (Edited)
Hmm...from the sounds of things, we have two possibilities, and it could be both.

1.) air leak, at least at cylinder #4
2.) injectors need some love

And indeed, this engine does use MAP's vs. MAF's. All MAP's have been replaced at some point recently, and the new post-throttle MAP is about a week and a half old. Currently the original one is in there, just so I could do a comparison test (readings are virtually identical).

If it is #1, i. e. an air leak, am I looking at replacing the intake manifold gaskets here? I haven't yet tried a smoke test, and that sounds like a good idea to do. Time to buy a pack o' cigarettes for the first time (no, I don't smoke)....

I also called up Paul over at Hurst Injector Service. He suggested something interesting. If an injector's flowing a bit rich, the fuel controller for that bank will lean-out the fuel-air mixture for the other cylinders...thus causing them to run lean, and thus possibly causing misfires. Given that I have often seen Cylinders 1, 2, 3, 5, and 6 go down, including in the most recent picture set...those symptoms would also correlate with Paul's idea here. He mentioned this before I told him about Cylinders 1, 2, 3, 5, and 6. When I then mentioned this observation to him, he said, "hmm...it's possible...that does fit what you're seeing."

So, all 12 injectors are going to get sent to Paul for cleaning. He agrees with @Astro14 in that they probably need it at this age. For $203 including shipping, I'd say that's not bad money at all. At least it eliminates one potential cause. If it's not that...then I keep troubleshooting.
 

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I hope that fresh clean injectors will solve this and make it run happy!! I did my spark plugs and one coilpack earlier this year, and my V12TT couldn't be happier. Thank God!
 

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am I looking at replacing the intake manifold gaskets here?
Hi T,

It could be around # 4 Cyl Port yes, but you do want to verify with smoke generator before buying any more parts, tearing down Manifolds or going for Injectors etc ;)

If you think it may be Injector, swap it with another Cyl first then see if that one becomes highest misfire count ;)

Bearing in mind this one Bank has higher Misfire Count than the other, it does look like an Air Leak, and likely in the area of # 4 Cylinders Manifold Runner, or maybe some remotely placed Vac Component / Lines to it if there is a direct Connection nearest to # 4 Port

HTH,
 

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2000 S430, 2003 S430, 2003 S600 TT, and 2005 E320 CDI
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Discussion Starter #49
Thanks, Dave. I'll do the smoke test this weekend.
 

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Discussion Starter #50
Couldn't do the smoke test due to too much wind. So, I got the fuel injectors out of there. The #9 injector broke while getting them out, but all the others came out OK. Apparently they're made by Siemens, though they don't have any Siemens marks on them, but both Paul and Google said this, so I trust that this is correct. Anyway, they're getting sent to Paul for maintenance, and the #9 one that broke, that'll be $85 for a new one from MBOemParts.com.
 

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Discussion Starter #51
Just heard from Paul at Hurst Injector Service today. He reports that the internal filters in all 11 injectors were so bad that if you touch those filters, they would crumble. The spray patterns were horrible, all over the place. I guess that's what happens after 175,000 miles of usage. He cleaned 'em all and put new, more durable stainless-steel filters in 'em, and they're now all flowing 92 cc's, plus-or-minus half a cc. Just like brand-new. He's going to ship them back tomorrow.

The replacement new injector for broken one out of Cylinder #9 is getting ordered today as well.
 
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