O2 voltage stays at 2.5V

[defrag010]

Hey guys, I need some help. With a logger, my ecu shows a 2.5v O2 reading even when the O2 is unplugged. With the multi-meter at the O2 input to the ecu, it reads zero, so it seems the ecu is “fabricating” this reading and sending it to the logger. We even tried a freshly rebuilt ecu…..same thing. Harness is ok. We even put a quick disconnect crimp on the o2 wire right outside of pin4 on the ecu, and when that is disconnected the ecu still sees 2.5V.

All I could figure is….
1. The ecu spits this in emergency, if there is no signal at all. (Hopefully)
2. The logger is wrong some how.
3. You add here….

One thing I did notice is that with the car running like that (runs like CRAP), the ecu will report a 2.96V reading, and will stay locked at that until the ECU is reset, then back to 2.5V.

Oh, the logger is an M100 with MMCD software.

 

[steve]

Hey guys, I need some help. With a logger, my ecu shows a 2.5v O2 reading even when the O2 is unplugged. Oh, the logger is an M100 with MMCD software.

Which of the two O2 variables are you looking at O2-R or O2-F?

Steve

 

[lewroe59]

Which of the two O2 variables are you looking at O2-R or O2-F?

Steve

the one marked on the pin out diagram as o2 sensor(vfaq).

 

[steve]

the one marked on the pin out diagram as o2 sensor

Are you helping Defrag?
You measured the voltage at the ECU pins? And it read what?

Defrag said he was reading the O2 voltage via MMCd and since it has two O2 variables I asked which one is being logged. Do you know?

Steve

 

[defrag010]

steve, we measured voltage at the ecu pins and there was nothing. We didn't measure it while the car was running because it ran like crap and the Throttle was about a second late in response and the car wouldn't hardly rev. We even disconnected the wire going to ecu pin 4, and the ecu still read 2.5V. I don't remember if it was O2-R or O2-F, the car is in lewroe's garage so he can check which one it is. MMCD displays the one that is on the bottom of the right column on the default first page. There are two O2's on the logger: the one on the bottom of the left column is un-selectable, and the one on the bottom right is the one that is reading this.

 

[steve]

Both are selectable, on a 1G you want to be looking at O2-R strangly mislabeled. It happens to be the one on the bottom left of the first page. O2-F is on the bottom right and will display whatever happens to be stored in memory on the ECU at 0x0040 (fuel trim low) on a DSM (on other cars it displays whats mapped to command 0x3e but a DSM maps commands 0x3e and 0x3f to command 0x3d)

The correct O2-R variable uses command 0x13 which maps to the value at 0x00e9 on E931 code.

You didn't see any voltage on ECU pin 4 with the car off because the O2 sensor doesn't start generating good voltages until it gets to about 600F.

Your chasing after ghosts. Log O2-R and let me know that you get. They we'll see if you should be looking somewhere else for the problem causing the car to run poorly.

Steve