Wideband o2 sensor reading suddenly not matching a/f ratio in DSMlink Please help

[rabenne]

I have a Zeitronix Zt-2 wideband wired into the rear o2 for logging with DSMlink. I also have the narrow band simlation wire hooked up into the front o2 sensor. Recently the wideband has been pegging lean and pegging rich, but the calculated "a/f ratio" in DSMlink wont match it at all... If the wideband is in the correct range for idle (14.7:1) then the calculated a/f ratio will be around 13.1:1. But when the wideband pegs lean for no apparent reason (18.0:1) the calculated "a/f ratio" in DSMlink cycles around 14.7:1.


So what is used to calculate the a/f ratio in dsmlink?

Since I have the wideband simulating the narrow-band why wouldnt the a/f ratio and wideband always match?

Until recently they usually were within .5 of eachother.

I have found a replacement sensor for $60 shipped but I dont want to fix it if it aint broke.

 

[rabenne]

Another note, any time I hit boost my wideband pegs to 9.7:1 and stays there until I let off. The calculated a/f ratio during boost ranges from 10.2:1 to 10.7:1.

 

[ToughTalon]

Is it pegging lean when you let off the gas? If you have the decel fuel-cut anable it will shut off the fuel injectors when you let off the gas and the A/F gauge will go full lean.

Its sounds like its going 'full' rich becuase it is pig rich. If you posted a log that showed this when it is happening it would be much easier to diagnose this problem. I would guess its a tuning issue though.

 

[twdorris]

So what is used to calculate the a/f ratio in dsmlink?

The two things you might expect...air and fuel. What makes the estimated A/F ratio so useful in ECMLink is the fact that it relies on accurate airflow and accurate fuel flow. If you get a situation where estimated A/F doesn't match measured, then it's because one (or more) of the assumptions are not valid. Those assumptions include a working (non-flaking) wideband O2, accurate airflow data, and accurate fuel flow data (injector size, deadtime, fuel pressure, etc.).

Until recently they usually were within .5 of eachother.

Check for boost leaks, then. If they used to match and then start diverging, that's an example of where the estimated value is so useful. It's telling you something has changed in your car that you might not otherwise have noticed right away.

I'll also second the suggestion to post a log showing examples of what you're talking about. But do so either on our support forum or in the log files "sub forum" here.

Thomas Dorris
ECMTuning, Inc.