S65 AMG misfires (not the usual)

LostKiwi

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Ah ok. Unlikely all three are down by the same amount. I guess injector is the next logical item then.
 
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alexanderfoti

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Grrr, took it for a drive today, still misfires.

ODB fuel trims are back to being lop sided too (-0.78 vs 0.78) not sure what star adaptions are looking like, not plugged it in yet.

getting super frustrated with this one.
 

LostKiwi

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Can you swap all the left and right injectors over see if the problem moves with the injectors?
 
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alexanderfoti

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Good idea! Think I will do that next.
 

KeithJG

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You said you are open to all.......i would do as Ian suggested just to clear the matter up over Plugs.

Fit NEW Spark Plugs even if that is what you have done.

Use Bosch instead of NGK if you can?......and knock the gap back?...... the misfire may be detonation due to high boost and a later spark?

I have always found misfire codes not accurate........you know it is misfiring anyway.

Going back to 1970 my Lotus Cortina, gave it a service and lo and behold it misfired up in the revs.

I replaced everything that i could and it still misfired......replaced the plugs with Ford own Motocraft plugs as should be and it was fine. After testing the new Champion Plugs on a proper pressure machine two plugs were duff.

I have never ever bought anything "Champion" since not even an air filter.
 

LostKiwi

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Use Bosch instead of NGK if you can?.
Funnily enough I will never use Bosch but will happily use NGKs! Had so many problems with Bosch when I was motor racing.....
 
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alexanderfoti

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You said you are open to all.......i would do as Ian suggested just to clear the matter up over Plugs.

Fit NEW Spark Plugs even if that is what you have done.

Use Bosch instead of NGK if you can?......and knock the gap back?...... the misfire may be detonation due to high boost and a later spark?

I have always found misfire codes not accurate........you know it is misfiring anyway.

Going back to 1970 my Lotus Cortina, gave it a service and lo and behold it misfired up in the revs.

I replaced everything that i could and it still misfired......replaced the plugs with Ford own Motocraft plugs as should be and it was fine. After testing the new Champion Plugs on a proper pressure machine two plugs were duff.

I have never ever bought anything "Champion" since not even an air filter.

Its had 2 sets of plugs, one NGK and one MB which are NGK's with an MB stamp on them. Behaved the same with both of them. I have been told not to gap the Platinum iridium plugs as its very likely to damage the tip and cause the electrode to fall off causing lots of engine damage.
 

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local parts factor carries a monthly trade mag for car mechanics.

"professional car mechanic"

its quite an interesting read, often has an article about troublesome cars.... intermittent misfire on the an Audi no one could fix was the ECU failing. 10 years back I would laugh.... nowadays is Std. for the ECUs to just go wrong

DTF !!!
 
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alexanderfoti

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Small update, Did a warm compression test, 170-180 psi on all cylinders.

I am removing the injectors, getting them sent to Mr injector who will flow test them and spray pattern test and clean them.

I will label them up and will install them on the alternative side when they are back to see if the problem follows.
 

LostKiwi

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170 to 180 is bang on the money for compression so that's good. We can rule out valves and pistons etc.
It will be interesting to see what happens with injectors.

If that doesn't change things I still have another couple of thoughts...
 
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alexanderfoti

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170 to 180 is bang on the money for compression so that's good. We can rule out valves and pistons etc.
It will be interesting to see what happens with injectors.

If that doesn't change things I still have another couple of thoughts...

I also did it with the Y pipe to the throttle body off, and planting your foot on the accelerator while cranking doesn't open the throttle body either, so that probably didn't help.

They are going to take a week or so to turn around the injectors, what are your other ideas?
 

LostKiwi

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Weak or broken valve spring?
Failing hydraulic lifters (pumping up).
Fairly long shots but if it's still #10 misfiring there's not a lot left!
 
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alexanderfoti

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Weak or broken valve spring?
Failing hydraulic lifters (pumping up).
Fairly long shots but if it's still #10 misfiring there's not a lot left!

I agree, lets see if the injectors change that behaviour. Keep in mind, number 10 only misfires on cold starts, and its not a proper misfire.

The full load misfires occur on 7-12, most of the time, occasionally only logging 10-11-12 but never only one one cylinder.

Data log attached, second gear to redline (full throttle past 4300rpm, van got in the way!):

upload_2018-3-12_21-21-12.png
upload_2018-3-12_21-21-37.png
 

LostKiwi

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Your mixtures are going hellishly rich at 4800 rpm! A lambda of 0.742 is an air fuel ratio of 10:1!!!

Also why does the MAF value dip at 4833 to 5016rpm?
 
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alexanderfoti

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Your mixtures are going hellishly rich at 4800 rpm! A lambda of 0.742 is an air fuel ratio of 10:1!!!

Also why does the MAF value dip at 4833 to 5016rpm?

I know, but Jerry at EC didnt comment on those straight away at least. see what he says about those tomorrow.

I am also not sure whether the lambda value reported via OBD is actual measured lambda, or calculated from the ECU map. I suspect it goes rich on purpose to fight detonation, whether its meant to go that rich or not...
 

LostKiwi

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If we had detonation wouldn't the knock detection circuit retard the ignition?
Ignition timing seems pretty constant.
 
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alexanderfoti

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If we had detonation wouldn't the knock detection circuit retard the ignition?
Ignition timing seems pretty constant.

Yes it would, but I believe its preventative in the tuning, as its mapped. By running it rich its less likely to det at higher rpm.

On a side note, I have a friend in the USA who drag races a few V12 MB's and his is tuned by Jerry. He has a wideband and observes AFR's in the low 10's at high rpm too. I would like it to be a bit leaner for more power but they are obviously doing it for a reason.
 

LostKiwi

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Do both banks have separate fuel rails or is it a single rail all the way round?
 
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alexanderfoti

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Also why does the MAF value dip at 4833 to 5016rpm?

No idea, car has no MAF's so its a calculated value from MAP and air temp.

Around that RPM is where the misfire occurred so it may be that, that we are seeing in the numbers.
 
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alexanderfoti

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