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Old 08-16-2003, 12:40 AM
mbc43amg's Avatar
mbc43amg mbc43amg is offline
Join Date: Apr 2002
Location: 40*-55'-44" N / 73*-24'-07" W
Posts: 125
What's a "good" ignition timing range on a C43?

Question to start off with... What's "more advance"? A larger negative # for spark advance or a smaller one?

I have my car set to RON93. The "official" objective of that is to change the ignition timing to run on lower octane fuel (according to the MB Star Diagnosis Computer). The real reason I do it is I find it gives my car much MUCH more power right off idle when I touch the gas peddle, as well as more peddle response overall.

I'm trying to find out if that is truly advancing the timing or retarding it from how it would operate if I was running in "default" mode, and by how much.

I bought the Car Code PC scanning software and OBD-II connector. I've been doing a good deal of data acquisition. I'm finding the OBD "SPARKADV" value [$0E] to vary between -10deg to -40deg. There's no true consistent pattern to "when" it's at -10deg vs. -30 to -40deg beyond when it's at low RPM, it's at low advance -- and it does seem that if I step on it, thus increase the absolute manifold pressure and MAF's measured flow, timing goes towards -10 deg shortly, then advance towards -40.

At idle, it's between -10 and -13deg. At a steady 30 mph in 4th gear (about 1500 rpm), timing's a steady -27deg. Interestingly, at a stead 90 in 4th, it's the same amount of advance. It only advances towards -40deg under hi-load and hi-rpm. Though again, there are plenty of times where I let off the peddle after accelerating, and only -then- do I see the timing jump to -40 for a few seconds, then back to round -27deg. my question to all those in the know is, is this "all good"? Is there an OBD-II value to tell me if my engine is experiencing detonation?

thanx much all,
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