A140 weird misfire

ruggy

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I have a 99my A140 with a misfire after an engine replacement, the engine was renewed with a complete second hand unit after the timing chain snapped but now the engine misfires once it is revved up, its fine at idle and will idle all day with no problem but once its revved up the ecu cut's the earth switch to injectors 2 and 3 30 seconds apart from each other, it can be either cylinder first and if the engine is restarted the concern disappears until the rpm is raised again. The only codes that are logged are p0302 or p0303, then these are replaced by p0300. The compressions on the engine are all 160 psi, the coil, plugs and injectors have been renewed and the maf/ecu sent away for testing with no faults found, the concern does not occur if the cmp is left disconnected or the maf is left out of the air flow and the engine does not misfire until the injector's are switched off. I have read about crankshaft adaptation on several sites but I do not have a dealer any closer than 45 miles away. Does anybody think it could be this adaptation that is the problem (flywheel from second hand engine fitted) or can anybody shed any light on this subject??? .
 

Alex Crow

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yes it could be that the sensor rotor adaptation needs doing, although this should happen in normal operation over time. presumably you realise that the injectors are being shut off because the ecu recognises missfiring on these cylinders. and that missfiring is detected by close monitoring of crank acceleration/deceleration between power strokes. so you have replaced the coil pack for no change? and the spark plugs too? ignition missfires are by far the biggest cause of p030* codes.
 
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ruggy

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thanks for your reply, yes the coil and plugs were changed because i suspected a ht misfire was causing the ecu to detect a slow crankshaft signal, even though the engine runs fine for the first 20 seconds or so with no misfires untill the ecu turns off the injectors. The engine runs fine with no misfires with cmp off or the maf out of the air flow but i suspect this is because it is in no sequential injection and that the ecu will run in a different stratagy with the maf out of the air flow( maf/ecu already tested). The vehicle cannot be driven as it is as it drops onto 2 cylinders after about 40 seconds above idle so i guess i'll have to transport it to a merc dealer for the adaptation or remove the engine again and refit the original flywheel from the old engine and cross my fingers and hope it works. thanks again for your suggestions. any further thoughts or suggestions are welcome. I need to fix this soon and i keep throwing money at it and getting nowhere.
 

Alex Crow

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no need to go to a merc dealer. tell us where you are, one of us may be around the corner...
 

mummyparker

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Please could tell me what the problem was.I am now having a similar problem with my aclass since the flywheel has been changed. Thank you.
 

allyjay

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I have the same problem with my A160 after replacing ring gear. Any ideas?? Star diagnosis shows faults with crank sensor rotor adaptation and misfire cyl 2 and 3 ?:confused:
 

WG M-B

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Get someone with star to carry out 'sensor rotor adaptation'. Beyond that possibly the wrong ring gear fitted
 

Alex Crow

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As above - should be simple as sensor rotor adaptation on Star.
 


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