M119.982 Spark Plug Gap
 

The spec for the M119.97x is 0.032" on Bosch F8DC4. But the M119.97x has a compression ratio of 10:1, while the M119.98x has a higher compression ratio of 11:1, and they both use the same heat range.

However, is the M119.98x spark plug gap narrower? Or is it 0.032"?

We always set the ME fuel system cars at 1mm.

That's 0.0393" (or typically 0.04"). As the spark center electrode wears, that'll get even bigger.

A couple of questions:

1. Have you found that this increased gap affects ignition coil longevity or gas mileage?

2. Now that our gas contains so much more ethanol (which on its own has a high octane rating and therefore resistant to knocking, but under high compression ethanol is more prone to pre-ignition), have you considered reducing this gap a bit?

1) No, actually increases fuel mileage. And a smoother idle.

2) If you drive on the autobahn all of the time OR run the engine at full RPM a lot, then going down to .9mm would be advised.

3) Copper core plugs should be replaced every 30K miles.

I don't mean to keep prodding you, but what's your opinion of E10 ethanol gas, and any adjustments needed to either the heat range or the electrode gap?

In California, it used to be 5.7% ethanol max. But, in January 1, 2010, 10% was optionally allowed. Since then, I've noticed worse gas mileage.

With ethanol, it seems reducing the gap would be prudent.

Have you heard any insider talk from Mercedes engineers (not marketing people) about what E10 is doing to our cars?