Question on reading O2 sensor....

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

Reply to
geronimo
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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?

Reply to
James Sweet

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

Reply to
Duane

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