My e220 m111 engine is pinking under light throttle usually when starting to ascend a hill and only seems to do it when the outside temp is 16 + deg.If I back off the throttle it stops but if I accelerate harder it turns into a full blown knocking. The head gasket was replaced two years ago and the maximum was machined off of the head. It has had a new wiring harness and I have just replaced the knock sensor. The engine always runs just over 80 deg with no overheating, performs well uses very little oil and no water. I drive it every day as a normal car and get about 27/29 mpg,which I think is a little low. Has anyone any ideas before I have to start and throw money at it again. Thanks Victor.
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grober
MB Master
What octane rating of fuel do you use? Skimming the head raises the compression ratio. One thing to try is running premium RON 98 octane fuel rather than the standard RON 95 octane. In the old days after a head skim you could manually retard the ignition timing by adjusting the distributor. Unless your engine ECU is ignition curve adaptive [ which on that vintage of car I doubt] it would require some sort of remap.
Thanks for the reply, I have already tried running on 98 but it made no difference. I was going to fit a new lambda sensor but I'm wary of damaging the exhaust as its been in for a long time. What are your thoughts on the sensor ?
grober
MB Master
At least the lambda sensor is easy to get at on the M111 engine but since it effects fuelling rather than ignition I'm not sure if it will help your pre-ignition problem. You could try running a grade cooler spark plugs or a different gap assuming you have the right heat rated plugs fitted AT PRESENT??? - I would recommend NGK
https://www.ngk.com/learning-center/article/207/i-have-slightly-modified-my-motor---do-i-need
https://www.ngk.com/learning-center/article/207/i-have-slightly-modified-my-motor---do-i-need
Fitted NGK BCP6ES spark plugs yesterday, heard a slight pinking when cold but will have to see how it goes. Looking on a plug chart the NGK plugs are one grade cooler than the standard Bosch F8DC4s,so could I go another grade cooler if the pinking persists ? Also the latest plugs I had fitted, bought from a dealer using my chassis No, are F-8DU4s made in France and not stamped with the Bosch logo. Any ideas ? With the NGKs fitted the car seems smoother when idling. Again any ideas ? Thanks Victor.
RichardF
Active Member
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Are you sure it's pinking, don't these engines have knock sensors that'd back the timing off?
I've never heard pinking turning into knocking, just louder pinking. That was running far too much advance on a car with a dizzy.
You could try a higher octane fuel.
The other thing to consider is the flex disc, they can make a light rattle turning into a full bore knock under more load.
I've never heard pinking turning into knocking, just louder pinking. That was running far too much advance on a car with a dizzy.
You could try a higher octane fuel.
The other thing to consider is the flex disc, they can make a light rattle turning into a full bore knock under more load.
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I had a new knock sensor fitted to try and cure it but its no better, I have also used RON 98 with same results. I had a new front flex disc fitted two yeas ago Ill have a look at it though. Also its still pinking with the NGKs fitted but running smoother !
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Pinking would only turn into a knock if something is getting extremely hot so that it causes pre-ignition.
To clarify the difference with the clue being in the proper name for each type of event:
[FONT="]Pinking or detonation is abnormal combustion that occurs after normal combustion has already been initiated by the spark. As the combustion pressure rises spontaneous combustion occurs in some parts of the combustion chamber before the normal flame front has managed to get there.
[/FONT][FONT="]Knock or Pre-Ignition is abnormal combustion that occurs before the normal ignition spark. In fact it can be a long way before perhaps not that much past BDC. Pre-ignition is initiated by glowing carbon or a spark plug that is too hot. Because the mixture is ignited far too early it builds pressure for much of the compression stroke and so can be very destructive melting plugs and holing pistons. [/FONT]
To clarify the difference with the clue being in the proper name for each type of event:
[FONT="]Pinking or detonation is abnormal combustion that occurs after normal combustion has already been initiated by the spark. As the combustion pressure rises spontaneous combustion occurs in some parts of the combustion chamber before the normal flame front has managed to get there.
[/FONT][FONT="]Knock or Pre-Ignition is abnormal combustion that occurs before the normal ignition spark. In fact it can be a long way before perhaps not that much past BDC. Pre-ignition is initiated by glowing carbon or a spark plug that is too hot. Because the mixture is ignited far too early it builds pressure for much of the compression stroke and so can be very destructive melting plugs and holing pistons. [/FONT]
Have you tried running it on high octane/super unleaded?
My 190E can occasionally pink when going up steep hills if I run it on regular. It had a cheap HG job done a few years ago; I am going to have it redone properly at a specialist when I have a replacement for the W211 I recently sold. In the meantime I'm running it on super.
I've tried everything to stop it and several specialists have looked at it. I've concluded it needs to have the head removed, rebuilt and it all put back together by somebody who really knows what he's doing...
My 190E can occasionally pink when going up steep hills if I run it on regular. It had a cheap HG job done a few years ago; I am going to have it redone properly at a specialist when I have a replacement for the W211 I recently sold. In the meantime I'm running it on super.
I've tried everything to stop it and several specialists have looked at it. I've concluded it needs to have the head removed, rebuilt and it all put back together by somebody who really knows what he's doing...
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grober
MB Master
NGK BCP6ES is the standard temperature plug for the the M111 If you wanted to go a grade cooler try BCP7ES NGK numbering convention is the cooler the plug the higher the number.
Fitted NGK 7s yesterday, slight improvement but still pinking.Onething I noticed,the plugs that I removed and have been in for 12 days,No 1 and 3 ceramic/electrode are still white and looked as though they were unused but No 2 and 4 are a light tan colour. Any ideas ?
grober
MB Master
White or light tan colour on the plug insulation normally points towards a weak mixture which can cause pinking - fuel has a cooling effect. This might be caused by several things--- a dodgy lambda sensor you mentioned previously-- blocked fuel filter- poorly performing fuel pump- partially blocked fuel tank outlet- faulty injectors or poorly earthed or faulty fuel rail pressure regulator.
The definitive test is to put a fuel pressure test gauge on the rail to monitor its pressure -there is usually a port for this and measure the fuel pressure over the rev range to see the injectors are getting a reliable supply.
grober
MB Master
White or light tan colour on the plug insulation normally points towards a weak mixture which can cause pinking - fuel has a cooling effect. This might be caused by several things--- a dodgy lambda sensor you mentioned previously-- blocked fuel filter- poorly performing fuel pump- partially blocked fuel tank outlet- faulty injectors or poorly earthed or faulty fuel rail pressure regulator.
The definitive test is to put a fuel pressure test gauge on the rail to monitor its pressure -there is usually a port for this and measure the fuel pressure over the rev range to see the injectors are getting a reliable supply.
