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Wrong! - Not that way! Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Tue, 18 Dec 2001 08:31:51 In Reply to: check your 005 AMM, mathiasB, Tue, 18 Dec 2001 06:15:01 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Sorry about the shout, but I don't want folks diving at their AMMs with tools.
If you want to adjust your AMM, or you are installing a new one, the manual recommends that you set it to 380 ohms first. This is just the starting point for adjustment that allows most cars to run OK.
From 380 ohms, you now adjust the AMM based on the output of the test point, which is a buffered output of the O2 sensor. You adjust the AMM until the O2 sensor output swings back and forth around 0.5 volts, spending 50% of the time above 0.5, and 50% below. If you use the buffered output, you get a square wave that you want to adjust for a 50% duty cycle. For this you need an analog meter, oscilloscope, or dwell meter.
The AMM setting may end up well above or well below 380 ohms - you're adjusting for the variability of each engine out there. I have seen John Moss, who heads Saab technician training, adjust a -005 AMM on a 900. He started at 380 ohms, and the O2 sensor was hardover. By the time he had adjusted it perfectly, the AMM was at 760 ohms or so. Nothing wrong with that setting - that's just where that particular engine with that particular AMM ended up.
So there's nothing magical about 380 ohms. If your car is running poorly, adjusting the AMM is reasonable, but you need to adjust it to make the O2 sensor output properly.
Good luck!
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