Bill Ball

From that chart Jon provided, it appears you don't have to be very lean to bump the NOX way up. So, the plugs may not be all that helpful. They probably will be nicely tanned.

worf928

Proving that a picture is worth a thousand words

Probst's Bosch injection book shows A/F values along the x-axis. The max NOx value is at about 15.5:1. So, only a little lean and the emissions test is screwed.

123quattro

Sorry to chime in late. I have some background in emissions and engine controls so hopeful can be of some help. It does look as if the engine is running lean. How lean and when is the question though. Narrow band sensors (like what the stock ECU uses for control) only tell you if you are toggling above and below stoich. I don't think there is much to be learned in looking at absolute outputs of the stock sensor. .1 vs .2 volts and .8 vs .9 is essentially the same thing. It shows the control is working. Trying to infer any A/F ratio from the voltages is really a stretch. If you really want to see what's happening, you need a wideband. The cats also may be oversized and not getting up to temperature, which would lower their efficiency drastically.

John Speake

Hello Dave,
I don't suspect the O2 sensor, or its wiring. Also the MAF is well enough in range for the O2 loop to function.

The range of the O2 loop is +/-20% or so around the nominal injector pulse widths.

Bear in mind the O2 sensor is working on an average of exhaust gas it sees. So I'm thinking that there may be some dodgy injectors, messing up the emmissions. e.g leaky injector (or even and igntion misfire) would pass unburnt fuel to the sensor, which would think "rich" and weaken out the mixture to the other 7 pots to get the average back to stoich.

worf928

This issue has been resolved.

Short story: carbon buildup. Solution: "BG" Treatment.

I'll post again later with more length.