I am trying to tune my MAF 6E car and I am having a weird problem. My O2 volts only rarely ever hold to a mv level plus or minus 100mv. What ususally happens is the mv will be normal around 600 for about 2 seconds and then they drop like a rock down to 4.44 (zero) for a half a second then return to normal.

This happens continuously although the timing of the lean event isnt really regular it just goes really lean every couple of seconds or so.

I am thinking that there is some kind of exhaust leak or maybe a vacuum leak that could cause this?? I just switched the O2 sensor to a heated one and the behavior is the same.

 

They're supposed to do that. The O2 mv should be constantly fluctuating above and below the .5mv level, that's how the computer keeps it running while you're in closed loop. In open loop the O2 output should be a lot more stable, but then the computer also can't adjust fuel levels for rich or lean conditions - meaning your tune better be real close in open loop or engine damage can occur....

 

I understand your explination but I feel that the O2 is bottoming out much more than it should. I will give a graph to show this tonight when I get home. I mean it looks as if more than 40 percent of all scans are with the O2 mv at 4.44.

I have seen other people's scans and I have to say that mine looks weird.

 

I had that same problem. Be sure to check for voltage drops on the ground side of the sensor signal circuit as well as the ecm grounds. I was chasing the same problem for about 3 weeks. I would like to see a graph ofthe sensor activity to see if it was doing what mine was.