i imagine this is something that would be in a bentley manual, but i can't afford one right now. i think its also referred to as "setting the base idle mixture."

i had been reading a steady voltage off my O2 sensor (0.80 volts), troubleshooting confirmed its functionality though. i decided to screw around with the adjustment on the AMM (very difficult to turn) and suddenly the voltage off the O2 sensor started fluctuating like i would normally expect it to. now it jumps around between ~0.35 and ~0.75, apparently someone had set it to the max rich setting...

i know on the 700 there is a procedure outlined in the faq section, but i don't have those test connectors on my jetronic setup, since its an 84 b23f i think i have LH 2.0, but i'm not sure.

Congratulations you fixed it!

Sorry if I steered you first to the ect and fpr in your other post, but the amm is usually not known to be the cause of full rich if not in limp-home (broken wire) or, as in your case, suspected of being "adjusted".

Your objective is to see it flip the voltage with about equal time rich and lean. The timing is hard to see on your DMM, but the test point (pink wire next to base idle test point) follows the oxygen sensor. You could put your meter there, too, just to see how the ECU interprets the lambda sond.

The idea of setting it to a particular resistance is an effort to get the mixture near enough to the range of closed-loop operation, which is what you see with your DMM on the sensor lead, flipping back and forth - should be about one cycle per second thereabouts.
--
Art Benstein near Baltimore

Here's how I handled my adjustable AMM on my own '84 240.

My replacement (new, not rebuilt) AMM (because the original was "fried" by the faulty thermostat in the air box, for which I promptly ripped out the whole mechanism -- but that's another story) came without a cover or seal for the adjustment screw. So I followed advice found on this list, and adjusted it* to give exactly 300 ohms, measured between contacts 2 and 6. Then I installed it, and miracle of miracles, it not only worked -- engine ran more smoothly than it had in years -- but it passed a NJ Emissions test a few months later with flying colors (despite 196K miles at that time) -- see below for details -- so I assume this adjustment for the AMM was right on!

[ * from the factory, it had been set at 390 ohms, but I changed it to the aforementioned 300 ohms.]

Dynomometer Test Results for New Jersey testing:
Gas Standard Reading
NOx 1227 33
HC 162 27
CO 0.91 0.02
CO2 -- 14.7

Hope this helps.

awesome! i can't wait to try it out.

so what order are the terminals labeled in, from the radiator to the firewall or from the firewall to the radiator?

btw - how is your gas mileage?

harley

Hi, again.

I don't remember exactly, but I remember that they were marked (very small, though).

I get a consistent 20 mpg, but I drive VERY hard all the time -- e.g., 75+ (sometimes 85) on highways most of the time, and often very high rpms -- I spend an inordinate amount of time accelerating and going uphill in 3rd (OD off); even around town, I spend a lot of time in 3rd or even 2nd; and I've got wider, stickier and heavier (i.e., poorer gas mileage) tires (Michelin Pilot Exalto PE2, 205/55-16, on Hydras). If I drove more sanely, and with stock tires, I'd probably exceed 25mpg, which is what my wife routinely surpasses (albeit in her '93 240, with "normal"-sized Michelin MXV4's).

"Dynomometer Test Results for New Jersey testing:
Gas Standard Reading
NOx 1227 33
HC 162 27
CO 0.91 0.02
CO2 -- 14.7"

These are great values. Curious but has the cat ever been replaced?
--
Norm Cook; Vancouver BC; 1989 745T 208,000KM

Yes, the cat was replaced in 2002 for the prior emissions tests, two years before these tests were taken in 2004 (NJ requires it every two years). But (from what I've read on this list) the cat primarily affects the NOx, and partly the HC -- the CO is almost totally affected by the AMM (which also affects HC), and these CO results are pretty good, I'm happy to say.

These test results were in 2004 -- I hope it does as well next year (2006) when I should have about 20,000 more miles by then.