Question on reading O2 sensor....

[geronimo]

I emailed about this before....my 92 740 turbo wagon is only getting
16 mpg after changing the O2 sensor. Thats' what the car was getting
before I changed it. The M.A.F. sensor also died and was replaced
recently, without improvement in gas mileage..

I y'ed a new wire into the signal wire of the O2 sensor, and ran it
into the pass. compt. With my el -cheapo digital DVM, when the car is
initially started, it showed abt. 550 mv, and dropped as the car
ran. It was not a stable voltage even initially. After a few minutes,
it was fluxing wildly/seemingly randomly, between abt zero and 600 mv.
When I get my FLuke 114 DMM, with analog bargraph, I'll be able to
properly monitor the signal.


I also need to know if the water temp has to get up to a certain temp
before the control system will go closed-loop. I am thinking they
probably are all like that. So if the car is forced to run cooler
than normal, can this prevent closed-loop operation? What is min. temp
forclosed-loop this car?

The Haynes manual shows that there is also some manifold air temp
sensor and a manifold air pressure sensor (besides the MAF sensor)....
Where are these two devices located? I looked for these two sensors on
Rockauto.com, they don't have them. I need to check/or replace *all*
the other sensors.....gas is getting expensive! THe car still has no
codes set...replacing the O2 sensor cleared the code that was set for
that problem.

Thanks, Geronimo

 

[James Sweet]

I emailed about this before....my 92 740 turbo wagon is only getting
16 mpg after changing the O2 sensor. Thats' what the car was getting
before I changed it. The M.A.F. sensor also died and was replaced
recently, without improvement in gas mileage..

I y'ed a new wire into the signal wire of the O2 sensor, and ran it
into the pass. compt. With my el -cheapo digital DVM, when the car is
initially started, it showed abt. 550 mv, and dropped as the car
ran. It was not a stable voltage even initially. After a few minutes,
it was fluxing wildly/seemingly randomly, between abt zero and 600 mv.
When I get my FLuke 114 DMM, with analog bargraph, I'll be able to
properly monitor the signal.

That sounds pretty much like what it's supposed to be doing. If it's
fluctuating wildly then it's working.

Have you ruled out driving style as the culprit?

 

[Duane]

With a new O2 Sensor and MAF, I'd concentrate that meter on the temp sensor
for the fuel ECU.

A drop to 16 mpg, if not lead foot related, is soon going to clog the
catalytic converter.

The 92's also have a cold start injector that may need attention.

Duane