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Discussion Starter #1
Im reading p300 codes, specifically p307,8, 9, 10, 11 and
p012 . entire left bank coding out. Car runs and idles perfect. 95 degree day driving around and sitting at stop lights idle perfect. Anybody have a good place to start?
 

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2000 SL500, 2001 S600, 2004 E320
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Are these misfire (P03XX) the only codes you read… no P0170-173 codes?

CEL is On I presume. I would start by clearing the codes, driving and see if they all come back and how quickly.

1998 SL600 is M120, one ignition coil per cylinder… not one coil rail per side… correct?
 

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Discussion Starter #3
Yes I did reset and drive again and the ce light came back on and read p0300, p0307, p0308, 9,10,11,12. This is a r129 and a single coil per cylinder
 

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1997 SL600 Brilliant Silver Sport with grey/dark metal interior, 234K miles
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The coils may be failing en masse due to the hot weather. All mine have been replaced (1997).

Swap some coils around with cylinders that aren't reporting misfire and see if the codes follow the coils.

As you pull coils, inspect the boots and check for oil in the spark plug wells.
 

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If this is massive ignition components failure it would be little odd that All of left side cylinders and None on the right side are misfiring. I would like to take a look at fuel trim values, self adaptations, Air Mass etc. to see if there is anything else going on.

I'm not sure what tools you posses but, perhaps this would be good time to invest in SDS, rather than guess. It would probably pay for itself in this instance and many times over in the future.
 

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Discussion Starter #9
62000 miles. Plugs are due to be changed. Today I’m going to pull the coils and give everything a good along with switching some coils to the other side. Anybody every try e3 plugs?
 

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94 E320 Cab, 93 400E, 87 300TD, 92 300CE24 Sportline, 94 SL320, 92 500E, 99 SL600R, '02 CLK55
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I would look for something common to that side of the engine instead of thinking that 6 coils and 6 plugs went bad at the same time. When I had these codes they were accompanied by fuel trim code for that side of the engine and a purge system code. Idle was rough and I found a vacuum hose off on that side of the intake.

It’s important to remember that the M120 has essentially two separate injection set-ups, one for the left side and one for the right side of the engine. I’d be looking for bad connections or a vacuum leak on the manifold and MAF that feeds that side of the engine - which is actually on the other side of the engine since the manifold crosses over to the opposite cylinder bank.
 

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1997 SL600 Brilliant Silver Sport with grey/dark metal interior, 234K miles
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It's just a diagnostic.

If the coil swap (very easy to do) doesn't reveal bad coils, then it is something common like a ground or a loose connection to that bank's ECU. Could be as simple as reseating that bank's ECU (after disconnecting the battery of course).

I wouldn't use anything but the recommended NON-RESISTOR plugs in the engine. Are the current plugs resistor?
 

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I would look for something common to that side of the engine instead of thinking that 6 coils and 6 plugs went bad at the same time. When I had these codes they were accompanied by fuel trim code for that side of the engine and a purge system code. Idle was rough and I found a vacuum hose off on that side of the intake.

It’s important to remember that the M120 has essentially two separate injection set-ups, one for the left side and one for the right side of the engine. I’d be looking for bad connections or a vacuum leak on the manifold and MAF that feeds that side of the engine - which is actually on the other side of the engine since the manifold crosses over to the opposite cylinder bank.
That's exactly what I was thinking. This doesn't sound like ignition problem. I would start by switching MAF sensors, clear the codes and see what happens.
 

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Discussion Starter #13
I check for vacuum hose problems then swooped MAF from side to side. Cleared the code and drove it for about twenty miles, no ce light yet. Will drive more tomorrow
 

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Discussion Starter #14
I switched the MAF sensors from side to side along with a few random coils. Reset and drove. 20 miles or so later lights back on the dash. Check the codes and nothing different 7,8,9,10,11 and 12 cyl miss firing. Car runs great, idles great and runs strong. What next???
 

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It's something common to all the coils like a bad ground or a loose connection to that side's ECU. There are 2 completely separate engine controllers for the V12, one side doesn't know what the other side is doing (by design).

Undo the center engine cover and trace both coil wires for each of the affected cylinders until you find the common ground. Then inspect the ground and the wires.

Remove the electronics box cover on the passenger side of the car at the base of the windshield and inspect, clean, reseat the ECU for that engine side. Use best practices when handling/servicing the ECU. Also, check the wiring to the ECU as it comes into the electronics box from the side. Look for frays, bare wires, anything amiss that doesn't look like the engine wiring to the other side of the engine.

Does the engine currently run resistor plugs?
 

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Discussion Starter #16
It's something common to all the coils like a bad ground or a loose connection to that side's ECU. There are 2 completely separate engine controllers for the V12, one side doesn't know what the other side is doing (by design).

Undo the center engine cover and trace both coil wires for each of the affected cylinders until you find the common ground. Then inspect the ground and the wires.

Remove the electronics box cover on the passenger side of the car at the base of the windshield and inspect, clean, reseat the ECU for that engine side. Use best practices when handling/servicing the ECU. Also, check the wiring to the ECU as it comes into the electronics box from the side. Look for frays, bare wires, anything amiss that doesn't look like the engine wiring to the other side of the engine.

Does the engine currently run resistor plugs?
Yes resistor plugs. I pulled both MAF sensors and cleaned them then put back on. Drove for a while and code has changed from p0300, p0307, p0308, 9,10,11,12. to P0170 Fuel Trim Malfunction (Bank 1). I switched the MAFsensors from side to side and still bank1.

Read more at: https://www.obd-codes.com/p0170
Copyright OBD-Codes.com
 

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Trying to diagnose your problem by codes alone would be nothing but speculation, possibly throwing parts at the problem and hoping for the best. These codes provide general direction what to test, but no more than that.

With the codes you have, my approach would be: First make sure basic service items are up to date. Clean and properly sealed Air filters, good spark plugs/wires, fuel filter…

Check for Obvious/visible Vacuum Leaks… like bad hoses, connectors.

Test the fuel pressure at injector rail.

Check fuel trim actual values, idle speed and partial load self-adaptations.

Read Air Mass values: at idle speed, 2000 rpm and full throttle under load.

This set of data would be good place to start in making more educated decisions how to proceed.
 
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