Which O2 Sensor
Senior Member
Joined: Apr 2001
Posts: 668
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From: Cayman
Originally Posted by Superchips_Distributor
Oh, and by the way - in our experience, as the O2's degrade (or are bad to begin with from the factory, as Marc's apparently were in his 2004 5.4 3V), it doesn't go richer in these trucks, they tend to do just the opposite - go leaner. We don't pay much attention to articles, what someone else finds, etc., we work off our own data, and aging O2's, just like a dirty MAF, tend to cause lean conditions, not rich conditions, in our experience with these trucks - just FYI.
Hey Mike I have been getting terrible gas mileage on my L. Probably my O2's are bad or worse yet, a heavy left foot. I havent notice any loss of power, but still want more power
hence my reason for calling you today. Probably since you have a L and you tuned mine probably you can help me out on the part number for my O2 sensor
Former Sponsor
Joined: Mar 1998
Posts: 13,385
Likes: 4
From: Virginia
Hi Guys,
First - Yes, it *is* possible for deposits on an O2 to cause it to give data to the PCM that would make it run richer than stoich in C/L (or at least increase the fuel trims and slow down response rate times), but when we usually find is that in O/L, they go lean - just FYI for clarification. This is precisely what happened with Marc's truck, his bad O2's, which were bas from the factory as best we can tell, caused his engine to not only run lean everywhere, but also to not accept tuning instructions like it should - his was a terrible mess, and an excellent example of why properly functioning & fresh O2's are so very important. I wish all of you could have been there to see that.
Next - As I clearly pointed out in my post about O2 sensors part#'s I found in that very quick and NON-THOROUGH search, everyone needs to look up their own part numbers for these O2 sensors - please don't ask me to do that for you. I suggest that you go back and re-read that post, as you will see that I made a number of points - not the least of which is the fact that the O2 sensor part # required can change on the exact same vehicle just based on model year alone, and that what I did was only a very quick & cursory search based on 1/2 ton 2WD's, and that each of you need to double-check to find your own Part# with certainty. So please - go back and re-read that post and then follow it, OK? Thanks!
Another way to put this would be to say "Give a man a piece of bread and he eats for a day - teach him how to fish and he eats for a lifetime."
Second - no, we generally do NOT need to worry about the downstream O2 sensors until they either fail, or they accumulate about 80K miles, whichever comes first. They are there primarily to check for the presence & function of catalytic converters, not for primary A/F ratio feedback. So we generally let the rear O2's go for 80K miles, and replace the upstream O2's, which are the ones that are responsible for primary A/F ratio feedback control and thus things like fuel economy, power, idle quality, etc., at 30K miles.
I hope that helps, & good luck!
First - Yes, it *is* possible for deposits on an O2 to cause it to give data to the PCM that would make it run richer than stoich in C/L (or at least increase the fuel trims and slow down response rate times), but when we usually find is that in O/L, they go lean - just FYI for clarification. This is precisely what happened with Marc's truck, his bad O2's, which were bas from the factory as best we can tell, caused his engine to not only run lean everywhere, but also to not accept tuning instructions like it should - his was a terrible mess, and an excellent example of why properly functioning & fresh O2's are so very important. I wish all of you could have been there to see that.
Next - As I clearly pointed out in my post about O2 sensors part#'s I found in that very quick and NON-THOROUGH search, everyone needs to look up their own part numbers for these O2 sensors - please don't ask me to do that for you. I suggest that you go back and re-read that post, as you will see that I made a number of points - not the least of which is the fact that the O2 sensor part # required can change on the exact same vehicle just based on model year alone, and that what I did was only a very quick & cursory search based on 1/2 ton 2WD's, and that each of you need to double-check to find your own Part# with certainty. So please - go back and re-read that post and then follow it, OK? Thanks!
Another way to put this would be to say "Give a man a piece of bread and he eats for a day - teach him how to fish and he eats for a lifetime."
Second - no, we generally do NOT need to worry about the downstream O2 sensors until they either fail, or they accumulate about 80K miles, whichever comes first. They are there primarily to check for the presence & function of catalytic converters, not for primary A/F ratio feedback. So we generally let the rear O2's go for 80K miles, and replace the upstream O2's, which are the ones that are responsible for primary A/F ratio feedback control and thus things like fuel economy, power, idle quality, etc., at 30K miles.
I hope that helps, & good luck!