OK - I know the O2 Sensor should read what it reads in the FSM...my questions is this:

If my car is running VERY rich will it top out at 1.0v or can it go past? Say, to 2.Xv.
If so, if it hits 2.Xv is the O2 sensor bad...it is not tossing any codes for it.

I have checked everything else in terminal 2 of the ECU (to ground 2C) and it all reads fine except for 2D and 2L...both higher than spec.

1988 S4 N/A Vert - Stock

As always, thanks in advance

 

Are you saying you're seeing 2.xx volts from the O2 sensor? Because in that situation, your O2 sensor is working... pretty damn well actually. It's reading a stupid rich condition then. An O2 sensor is a galvanic battery, and generates voltage based on oxygen/fuel content in the exhaust. If it fails, it does so by not producing enough voltage, or none at all.

Find out what's causing this stupid-rich condition and fix it.

 

Cool-wasn't sure on that; eliminates that one.

Nothing like huffing gas while driving at 12 MPG

 

Oh yeah - like 2.4 - 2.6 uhhhh

 

MAP (mazda calls it "boost" sensor...) sensor, AFM, spark plugs, injector stuck open, coolant sensor, FPR failed shut... I mean, the list can go on for a while.

The best thing to do to eliminate a bunch of things all at once is to grab the FSM and back probe the ECU connector (at the ECU). The FSM has a chart of all the expected voltages. Start with just the inputs. If anything reads 0v or 5v, you've found an issue and you need to pull that thread. And the S4 won't have a check engine light. Checking codes on it is pretty pointless in my opinion.

 

It will make for a nice little weekend project. Have the homemade code checker, was fun to make but that's about it.

I'll see what I find and post back.

 

Narrowband O2 sensors have 0-1V output. I don't see how you're getting ~2.5V, and if so, I would call that bad. When does it read this voltage? I'd check it at idle, then open/close the throttle. As the revs drop, it should go lean (lower voltage). The ECU could be at risk if it's suddenly dealing with the current increase associated with higher voltage.

The good news is that the O2 sensor does little on these cars. It is used only when cruising at low throttle.

 

I still think that there's no way you can call it bad if it's pumping out more voltage than it's supposed to. It's probably going to die soon anyways because of the over-rich condition. I've never seen one put out that much voltage though. RR88's right though, they don't really do much anyways, and when it does, it's only when cruising.

 

It reads 2.4/5v at idle and while driving it will flux between 2.3/2.6

 

I can double check but i'm pretty sure it was increasing while accelerating.
Misread what you typed, anyway... it is way high.

 

Ran through the ECU a few minutes ago. Everything checks out sans the O2, IAT and now the AFM. O2 and AFM are off the charts whacked out...reading 40-50-60...jumping all over the place.

IAT is sitting ~1v high

Tested the ECU to the grounds on the ECU and checked the O2 and AFM grounded to the car and still jumping. Going to pull the AFM and test against FSM spec.

 

AFM was toast at flap wide open and the temp based spec - replaced with one I had in the trunk that is within spec. Still rich as hell but now need to readjust idle. Hovers around 1500 so I'll get on that...

The L/R adjustment by the air box is reading 4v @ ecu which I assume is RICH and 1.0v is LEAN and still has the factory goop in it. From reading other post I am a little hesitant to start messing with it...or am I just being a pu$$y?

 

Located the problem. Rear rotor has died...one puff @ ~30psi and then nothing