Hi Bob,

1-Pulled blade fuse mounted on front left fender to power down the ECU. Powered up and checked for a 1-1-1 signal. This was confirmed.

This doesn't really tell you anything. Doing this will always result in a 111. What I was asking you to do is reset the ECU, and then operate the car until the fault codes came back (113, etc.) to make sure you do indeed have a persistent trouble.

2- Pulled spark plugs and found them all to be coated with carbon. Replaced puls to continue with testing.

Black plugs indicate rich, but your sensor readings (the millivolts) indicate lean. Something is not working in the oxygen sensor area... But the black soot is still there from when the computer decided it wasn't getting good info and gave you a default rich limp-home mixture.

3-Checked O2 sensor heater resistance. Was 15.5 ohms. OK, you want to check this resistance quickly after running the motor and see it fall as the sensor cools. Looks like a warm reading, indicating the sensor is getting hot.

4-Started engine and measured heater exhaust voltage at 14.5 volts which was due to system voltage increasing to the normal charge level.

Is this where you measured the voltage across the white wires to the oxygen sensor while the sensor was connected?

5-Measured O2 sensor to ground voltage to ground. At idle voltage was 35 to 38 millivolts varying. Increasing engine speed sent the number up to over 110 millivolts. When at idle, opening oil fill cap caused small change in output to 45 millivolts for about 3 seconds and then the reading returned to 38 millivolts. Shut engine down.

Here there's a problem. It should be oscillating about once a second between roughly 200 and 800 mV, not 35 and 110. You were measuring this with the sensor connected (green wire to black wire) right?

6-Used mode 3 on ECU to check operation of injectors and air bypass valve. All parts responded with appropriate noise as expected.

That's good.

7-Pulled blade fuse for 3 min. Replaced fuse and started engine. Check engine light came on after about 10 min idle.

OK, missed this first read. Did the same codes, i.e. 113 return?

8-Shutdown engine and removed AMM harness plug. Measured resistance between pins 2 and 3 (burn off wire function on engine shutdown) according to Bently book and found the resistance to be 2.9/3.0 ohms. Bently says it should be 3.5/4.0 or replace the AMM

This test is supposed to find an open platinum wire, but the reading actually looks at a precision fixed resistor and not the wire. It is a useless test. Just look in the AMM to see if the wire is broken.

9-Measured the idle air base line resistance between pins 2 and 6 (idle air potentiometer). The measurement was and open circuit. Bently says it should be between zero and 1000 ohms or get a new AMM. Numbers on AMM are...

This 2-6 resistance is for the older AMM's with a mixture pot. Yours doesn't have one, and does not even have a pin 6.

You may indeed have a bum AMM, but nothing you've measured proves it. The best proof is to substitute a working one. Everyone with only one LH Volvo should have a spare AMM tucked away for this reason. Buying one when you are in a hurry will always cost you more.

Try this test: Disconnect the AMM from the airbox elbow. Pull the boot back on your AMM connector so you can reach the terminals with your voltmeter probes. With the key on, but motor not running, measure the voltage at the white/red wire, and waft some air toward the AMM intake and see what the response is. You should see about a volt and a half, and the reading should move upward as you create some wind. This doesn't confirm you have a good AMM, but lack of this reading or response will confirm a dud.

If it wasn't for the lean oxygen sensor readings, I'd ask whether you've checked the engine coolant temperature (ECT) sensor output. Usually those open up, which would make sooty plugs and high (rich) oxygen sensor output.


--
Art Benstein near Baltimore

The quickest way to double your money is to fold it in half and put it back in your pocket.