Hello Dave,

Excellent work! I think you've identified the problem.

"1. The yellow wire (term 12) shows 2.27v and this is in the high range of 0-2.6v.

2. The red/white wire (term 7) shows 1.57v right in the middle of the range 1.2-3.5v.

3. The black (term 36) and green/yellow (term 6) are both grounds. So no voltage but both show continuity to ground individually and continuity to each other.

4. The orange wire (term 9) shows battery voltage 12.8v as expected.

5. The white wire (term 8) has no voltage spec in the book but I got minimal of .02v.

With the same setup except with the engine running I tested voltages:

1. The yellow wire still looks good and as I turn the AMM screw the voltages change within the expected range. So whatever is attached to the screw seems to work right.

2. The red/white wire show 4.15v at idle (which is low and rough) and this increases if I engage the throttle. This is far over what I expect from the book which says 2.7v at idle and 3.5v at 3500 rpm. Could it be that the AMM is trying to send a powerful signal to the controller to lean the mixture out? It is very rich and smelly despite everything.

With the same setup but the key off entirely I tested resistance:

1. Between terms 6 (green/yellow) and 12 (yellow) the book says 0 to 1K ohms. My readings (using the 2k range on the meter) were .280 to .363 so I think that is basically ok.

2. Between terms 6 (green/yellow) and 36 (black) - both grounds - the book says 2.6 to 4.0 ohms. On the 200 range on the meter, I get .1 to .3 ohms. I am not sure how to interpret this.

Then I decided to follow the suggestion made to check the coolant temp sensor under #3 intake. The book says to find the blue wire in the big, tape-wrapped wiring harness along the firewall. And then to probe it with a needle and check the voltage between it and ground with the key on (engine not running). The book says 0.1v with the engine hot and 3.2v at 20 degrees. It also says a voltage of 4.5v is bad sensor, disconnected, bad wire, or bad terminals. I get .45v. The engine is not very hot since only ran a few minutes while testing above. So maybe this is an ok reading?"

That idle reading is the one out of whack. Your AMM is sending a signal to the ECU to dump lots of fuel in, as if you're going up a mountain on the expressway. The reading 4.15V should not be seen by someone standing next to the car unless it is on a dynomometer. The rest of your readings are OK, so I believe you have a faulty AMM, and it makes me glad you went ahead and took the idling readings in addition to my suggestion to take the engine off readings. With engine off, the AMM looks OK.

There are two characteristics to the amplifier controlling the temperature of the hot wire, offset and gain. The engine-off reading is a gauge of the offset, and a creep in this voltage I've found due to the moisture ingress through the silicone on the hybrid microcircuit. But the gain is most affected by the condition of the external elements -- the hot wire and the reference resistor in the bridge, and so far I've not encountered any AMM with the response yours is giving at idle.

My bet is on the AMM.

--
Art Benstein near Baltimore

I'm reading a book about anti-gravity. I just can't put it down.