Hi Larry! I read your thread regarding gapping your plugs @ .038. Did you make any adjustments i.e. lamda setting etc. to correct up running lean or rich? I have a 1989 300E (Federal) and use the copper plugs called out in my owner's manual. I'm going to try your suggested gap but I would like to know if this creates changes that need to be adjusted for. Thank you Larry! Josies Dad

I have made no such changes. I went to copper core and .038 at the suggestion of one of the pro tech's here. My idle smoothed out and the car has never run better. I believe that if you have to make a tuning change because of spark plug gap, that there is another variable in the equation somewhere.

Good luck,

Thank you Larry! Josie's DAD

plug gap
 

Larry,
I believe the gap spec for this engine is .031 or so. Did a gap difference of .007 really make that much difference? .. or was it because you were using the wrong plug?

barrie

I don't remember the gap spec., but I think that it is .034. The gap AND fresh copper cores did smoothe out the idle, no question. These engines do not have the super high energy igitions of many other cars of the eighties.

The broad electrode of the copper core plug with the SLIGHTLY opened up gap does smoothe the idle. If there was more ignition energy, you could probably open them to .050 or more and help immensely. I believe that this is an engine that would respond well to an aftermarket ignition system.

There have been a number of pro techs here that have recommended this gap setting and it worked for me.

Have a great day,