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You're only half-way there Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Tue, 22 Feb 2005 05:50:04 In Reply to: After 2 minutes..., Rmc, Mon, 21 Feb 2005 18:54:50 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The magical 380 ohms on the AMM is only the starting point. That setting on the AMM will permit most cars to run. You now have to adjust the AMM to your particular car. Anders has a post on this:
http://www.saabnet.com/tsn/bb/900/index.html?bID=210522
The AMM controls 100% of the fuel flow; the O2 sensor about 25%. The O2 sensor works in a very narrow range. You 'coarse adjust' the AMM to get the mixture near right, and then the O2 sensor takes over. If the AMM is set too rich or too lean, the O2 sensor doesn't have a chance to work.
There are two ways - one is to put a voltmeter right on the output of the O2 sensor (while it's still connected!) and adjust the AMM. The other method, as Anders writes, is to measure at the Test Connector. The test connector is just an amplified and squared-up version of the O2 signal. Basically, you want to adjust the AMM until the signal on the test connector starts to bounce between 0 and 12 volts. Ideally, it would spend 50% of the time at 0, and 50% at 12V. Without knowing the sample and update rate of the digital meter you have, the best you can do is get the voltage to jump around - it shows that you've got the O2 sensor working.
As said, that 380 is only a starting point - I've seen cars tuned perfectly with resistances well over 700 ohms.
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