I recently read a post on Oxygen sensor cross counts for a 4.9L. I could not find it again. Here is my problem. I failed my Mass. Emissions. I failed the first two parts. The NOx #s were good. I’m Sorry I left the test results at home. Long story short I changed out the two O2 sensors. Now I’m watching the #s on my computer and here is what I’m seeing. I just do not know what to make of the #s.

The reason I’m looking at these #s are because the one code I had was PD39 rear block learn fuel 128.

These #s were taken after driving about 30:00 home from work and I had the same #s this morning.


PD32 front oxygen sensor voltage is reading .45
PD33 rear oxygen sensor voltage is reading .45
PD34 front oxygen sensor cross counts 0
PD35 rear oxygen sensor cross counts 0
PD36 front fuel integrator 128
PD37 rear fuel integrator 128
PD38 front block learn fuel 128
PD39 rear block learn fuel 128

Should I be seeing this #s move? Sorry for long post.

I am looking at my FSM for my 90 Allante which is similar as follows:

A voltage of .42 to .48vdc is the ECM reference voltage. The O2 sensor must generate a .15 volt greater than the reference to register a O2 Sensor Cross Count in the ECM. If this is the case you should be throwing a DIC code.
Also the 02 sensor voltage holding a steady .45vdc indicates that you are in open loop mode.

Do you have any DIC codes?
Have you tried running it hard to light off the Cat? If the car have been driven on slow shot trips, this combination is notorious for fouling Cats.
Has gas milage been bad?
What is your fuel pressure? A bad reg could cause these types of problems.

Factory Service Manual for my 1990 had fairly complete diagnostics for failed emissions tests. I had high NOx which led me to the EGR valve - but only after I'd replaced the cat. eBay is often a good source for FSM or www.helminc.com

http://www.cadillacforums.com/forums/cadillac-deville-1985-2005-including-1985/132366-oxygen-sensor-cross-counts-4-9l.html

Blue eldo,chubbyranger and Cadillac Al thanks for the replies. I also changed the rotor and cap, fuel and air filters and oil. After driving it for about ten days, my gas mileage went up 2 miles per gallons.

I went down for my retest today and passed. New #s.

HC 00.98 limit 01.20
CO 011.72 limit 020,.00

Thanks again for the info. This is a great site.