O2 sens/AFM/Exhaust - Learned something 2day.

[cygnusx1]

I made it a mission tonight to get out my voltmeter and tinker with the AFM while watching the O2 sensor voltage. I also wanted to get rid of the annoying squeak in the rear hatch area that came when going up hills and then went away only after parking the car for a while.

 

O2 sensor story:

I wanted to see where I was after I read a nice webpage about O2 sensors and tuning with them. ( http://www.datsuns.com/Tech/oxygen_sensors.htm ). So I hooked up the meter and let it warm up it was reading about 0.3 -0.6 volts and swinging between the two numbers erratically. As it idled I manually moved the AFM pickup and watched the voltages change. So now I know it is working. I richened the AFM until I got a solid 0.8 volts at idle and at about 2500rpms. I went for a ride. It was running too rich. I came back and leaned the afm to try to get about 0.5 volts. As I approached leaner values, all of a sudden the volts started jumping around again between 0.2 to about 0.6 I thought that was weird but then again I thought maybe when you reach stoich, the sensor starts swinging back and forth through a range and correcting to maintain a good mixture. I also noticed that during this voltage swinging the green LED on the ECU flashed almost in time with the voltage. Hmmmmm. I think I get it. When the O2 sensor is in "range" it swings voltage back and forth and as it does this it flashes the green LED on the ECU. I went for a ride and it was flashing the LED when cruising and at idle. At full throttle the LED was not really doing much. Sometimes it was off and others on but mostly off. Bottom line it that it runs sooo sweet and smooth power from 2000rpm all the way through boost with no lurches or burps or anything. I think I got it!!

 

Strange Hatch squeak:

Loud creaky squeaky from he hatch area ONLY after going up a long hill. Once it started being noisy it would not go away until the car was parked for a while. I went through everything, bushings, interior, struts, gas tank, you name it. You know what it was!!! The exhaust system expands when it gets hot from going uphill and the muffler touched the inside of the rear valence!!! Once it cools, there is a 3/16" gap. It really grows with the heat!! It was not the motor shifting back. It is heat related.

 

OK time for a typing break. I learned two things today.

[CruxGNZ]

Strange Hatch squeak:

Loud creaky squeaky from he hatch area ONLY after going up a long hill. Once it started being noisy it would not go away until the car was parked for a while. I went through everything' date=' bushings, interior, struts, gas tank, you name it. You know what it was!!! The exhaust system expands when it gets hot from going uphill and the muffler touched the inside of the rear valence!!! Once it cools, there is a 3/16" gap. It really grows with the heat!! It was not the motor shifting back. It is heat related.[/quote']

 

Haha... I had the same problem! The muffler was about 3/16" from the rear metal also. But only happened when I ran it very hard in the city, or when I took the car for a trip longer than 20 minutes on the highway. It made this horrible metal squeeking sound, it gave me goose bumps like figernails on a chalk board.

 

It took me a while to figure out what the heck that noise was from, because I couldn't duplicate the sound when I parked it. It was rather interesting to find out that the exaust expanded that much.

 

!M!