NGK Canada published a TSB in 2006 in which they state that due to ethanol being introduced in gas, drivers have been reporting these symptoms:

1. Reduced gas mileage
2. CEL light, code showing lean condition

They recommend the following to remedy both issues:

A. One step colder
B. Narrower gap by 0.010", not to go below 0.035"

For my vehicle, I've done the following:

- One step colder
- Narrower gap by 0.004" (factory spec for my M119.982 is 0.032")

So far, after two tanks of gas (several hundred miles), my mileage seems to be better, the insulator is still too white for my liking (indicating still a lean condition), and the ground electrode reading shows color change at the turn of the elbow (but closer to the ring, which indicates it's still slightly hot).

Btw, the spark plug gap is a debatable topic. This is my take:

Reduction of the gap is necessary in E10 gas for the reason that ethanol--while it is detonation-resistant--is more susceptible to pre-ignition at higher compressions. My M119 having 11:1 compression ratio and achieving greater than 100 KPa, the possibility of pre-ignition with ethanol is greater. (Maybe this is why Mercedes says their knock sensors can't handle lower octane gas?) The possibility becomes even greater knowing that gas stations sometimes goof up and pour the wrong octane gas in their underground tanks.

However, my M119 uses non-resistor plugs, and the coil connector provides 2K Ohms. Narrower gap effectively decreases resistance. This may cause potential electronic interference with the ignition system. When reducing the gap, using resistor plugs (which will have 5K Ohms) might be a good idea.

I'll report more on my experiment as time goes. After evaluating this set, I'll try going another step colder with a resistor plug.

Attached Files

ngksp-0506-3_-_automotive_ethanol_fuel_en.pdf (180.7 KB, 119 views)

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