Signs of a failed or failing O2 sensor are...

[Ross-N-Chicago]

I replaced my cat last week with a Dayco from Summit after 200k+ miles. Here are the latest symptoms that I am troubleshooting since the install:

Bad Mileage, down to 11-12 in city
Poor acceleration from stops or slow speeds
Bad low end rpms with shimmy at 15-1700rpms on highway in OD
Replaced FPR but did not solve problem
Plenty of black soot at tailpipe
Cat seems to run cool

Should I replace the O2 sensor as the next step and get the codes read too? I can't find my f***** code reader since I moved. I am so pist right now.

 

[Nate1]

Seems to me like you've already spent more than the $80 dealership diagnostic fee to have them tell you what it is, but those are the signs mine exhibited (with a rough idle).
Good luck!

 

[james t]

if the cat is cool, and you are getting bad mileage/raw fuel in the exhaust, then you are definately running rich. could very well be an O2. have you ever replaced them? if not, then with 200k it is way overdue.

also, have you tried cleaning the MAS? this can also make the truck run rich.

 

[Ross-N-Chicago]

I am 100% the MAF is clean. My guess is that the FPR or O2 sensor failed pretty close to when I installed the cat--coincedence. I am going to read the codes first as soon as I find my code scanner. Can a bad O2 sensor cause this w/o setting off a CEL?

For posterity, I will clean the MAF again just to be sure.

 

[james t]

Autozone will read your codes for free. in theory anything operating out of tolerance will set off a CEL. in real life, alot of times things go bad without throwing a CEL. average life of an O2 is around 100k. if you've got 200k on your O2's then its prolly time to replace them.

 

[aldive]

O2 sensors can indeed cause all sorts of difficulties without triggering the CEL.

Good luck.....

 

[Ross-N-Chicago]

Thanks Guys,

It just dawned on me that running a couple cans of PowerFoam and two cans of SeaFoam probably killed it. I replaced the last O2 in the Fall of 2001 so I am sure that's it. I swap one in tonight and let you know if it fixed it.

 

[EliteConcept]

does a bad o2 sensor make you idel ruff?

how much are they?
i got 130k on the x now, i should replace mine pretty soon...milage is ok about 16.5 average.....but got this constant ruff idel that i can't get rid of for hte life of me..

 

[Nate1]

They run from about $50 (I believe) to $80 per oxygen sensor.

 

[Ross-N-Chicago]

Ran codes and 157 popped up, MAF voltage too low. So I checked the connection, Thanks Nate for inspiration, and the electrical connector was barely on. Ziptied it nice and tight since I broke one of the pins and now it runs just like it should. Looks like I put on a new FPR and O2 sensor for nothing, but it never hurts.

Thanks for all your help.