I'm just a newbie who's trying to get the mixture set right on my '87 420SEL. I'm trying to avoid buying a duty-cycle meter if possible.

The car was running a little too rich to pass the smog inspection, but it almost passed. Based on the numbers, the smog shop said they think I need a new cat converter.

Now I had heard that adjusting the mixture 1/4 to 1/2 of a turn was a big change. However, I've probably leaned my car out over a turn already. Each time I lean it out it seems to run better, and the hesitation on acceleration that I was experiencing went away.

My question is, should I keep on leaning it out, or not? I'm wondering if maybe I leaned it out some more, it might pass smog without having to buy a new cat. But if I get it too lean, will I burn a valve or something? Or will it become obvious that it's too lean because it will start to die at idle? How about if I lean it out until just before it starts to die at idle? Would that be too lean?

Thanks for your help.

A duty-cycle meter will tell you if your O2 sensor is even working. How's your gas mileage?

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma

I think the O2 sensor should be working, because it is new. The car has been gone over by a very good mechanic, Ernie in Orangevale, CA, who thinks it is basically running correctly, and I agree. (A lot of work was done, and an effort was made to replace every defective unit on the engine, unless we missed something). The smog shop man said it is running really nice and smooth, and the only reason it didn't pass is because it needs a new cat. The gas mileage is good.

Every time the smog man leaned it out a little, it came closer to passing. I'm wondering if maybe he just got tired of dicking with it.

Did you read the link I posted? That should tell you where you want to be with the mixture, and all you need is a 2.99 harbor freight multimeter.

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual

"Did you read the link I posted?"

Oops, sorry, E150GT, I must have forgotten about that link. Would you please point me to it again?

Thanks.

Smog Shop Won't Adjust 420SEL Mixture

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual

Oh, yes, E150Gt, I did check that thread out, but unfortunately it was incorrect. Would you mind double-checking the link you intended to refer to, and re-posting the correct link?

Thanks a lot.

OK here it is. Who knows how that other thread go there. http://landiss.com/mixture.htm

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual

Thanks a lot, E150GT! That was a really good thread. No need to buy a duty cycle meter. I'm going to use my analog Volt-Ohmmeter, and then convert the average voltage reading to a duty cycle figure by using the formula in the thread. I like an analog meter much better than a digital one for measuring the average value of square waves. Of course, meter damping is a factor, but generally it's much more accurate to use an analog meter for measuring the average value of square waves than trying to take a mental average of the two voltages that a digital meter would flash at you.