Originally Posted by christuna

Leaner than it should be will result in lower combustion temp = less prone to knock

Again these engines run at the hottest mixture.

Originally Posted by Diseasel300

You're clearly the expert here. Enjoy your thread. Some hands-on experience in engine tuning might help fill in your knowledge gaps in the future. I have better things to do with my time than argue with an armchair expert.

Originally Posted by christuna

I think that the temp spikes might be causing these codes because the ignition module retards the timing depending on the engine temperature. Even the old ezl's do that. A good fan clutch will keep your engine temp at 87c in a 90f traffic and will disengage once you get up to speed.



It's a myth that running lean = running hot.

I don't think that a vacuum leak is contributing to a possible knocking condition and here's why:

These cars run at the hottest mixture setting from the factory (which is 14.7 or 0.068 fuel air ratio on the graph) anything leaner or richer than that runs cooler.



Left side is lean and the right side of this graph is rich.

The reason why they run at the hottest setting is because of emissions and fuel economy. That's where they try to keep the narrowband o2 that the w124 has.

If you have a modified engine you want it to run rich but you don't want it to get to 14.7 while under heavy load because that's the hottest mixture. Leaner than that is cooler.