RngTrtl

Dear All, (1985 US, 32V, Auto)

Well, I got my gauges installed and the AFR gauge (Autometer Phantom series) acts relatively erratic. I have a similar same gauge in 2 other cars and am very familar with how the gauge is "supposed" to read. In the my 928 however, the gauge seems like it is always "tracking" where it is suposed to go it just never settles down and is always bouncing around where it should be. I would think that if my AFR was really as jittery as the gauge is senseing that my car would run like poop so I think that I am picking up interferance somewhere. BUT I used shielded cable all the way down to the computer where I picked up the signal wire at and I tap the signal input for the gauge at the green whielded wire for the o2 by the computer and I also attached the shield of the input to the shield for the o2... In my head everything should be working fine, Can anybody think of anything that I am missing? Do I need to ground the shield again to the chasis by the computer? Thanks for the help.

928drvr86.5

My Autometer AFR does the same thing, i think i read in the Autometer manual that it is normal.

AO

I'm not familar with that particular gage, but I had a Split Second AFR gage before and it does tend to hunt around a bit connected to the stock O2 sensor. I'd say it's normal for it to vary at idle from 14.3 to 15.5. My Innovate WBO2 sensor fluctuates from 14.5 to 15.0 at warm idle. Hope this helps.

928drvr86.5

Per Autometer installation instructions, "When the Engine is at heavy load the moniter should indicate rich. At cruising load the minitor will appear to be bouncing back and forth between rich and lean. This is normal......."

928drvr86.5

Also... "Since the oxygen sensor output is very accurate and sensitive at the STOICH A/F ratio, it will cause the A/F meter LED's to bounce back and forth rapidly." I thought that it should be steady myself when I first installed it.

Louie928

Without seeing exactly what's happening, I think it's normal as others have said. Check it at WOT when the LH is in open loop and not controlling the mixture. It should be steadier. The LH automatically perturbs the mixture, then tracks the change recorded by the O2 sensor. That's how it knows the O2 sensor is connected and working. The mixture should be fairly steady when you first start it for about a minute or two. Then the LH begins operating closed loop and you'll see the mixture hunting.

mark kibort

the guage is not doing anything. its the 02 sensor and the ECU closed loop that is creating this phenonenom. the ecu will measure the mixture and the ecu will tell the injectors to flow more fuel until the mixture is full rich, then the fuel is cut off where the mixture is full lean. this cycle happens 10 times a second! the average mixture ends up to be near stoich for best fuel economy and deposits reduction. when you go near full throttle, the system will go open loop where you will notice the ARM sensor showing full rich (near 12 to 13:1) you can also remove the O2 sensor, and have the mixture at full rich all the time (no hunting of the sensor lights), but your gas mileage will suffer
mk

A.Wayne

If the gauge is going back and forth indicating a change in mixture , this will be from the close loop operation of the factory ECU, if it bounces widly an irratically from very rich to very lean, this is a sign of uneven burn in the cylinders ( mis-fires ) from the uncontrolled combustion.......

RngTrtl

Well I guess it is settled then, it is acting normal....It is weird to me though on my truck and my (brother's and I) XR4ti the gauge does not bounce around at all it moves across the perimeter of the gauge with a definite purpose, very precise so to speak. In the 928 it moves in the appropriate fashion like in the other two vehicles, it just seeems too erratic to me. But having cunsulted the master this appears to be the norm in the 928. Thanks for the help ya'll.

John Speake

Different makes of gauges may have different smoothing on the display which will affect flunctuations seen.