Faulty MAF and before CAT O2 Senors and no light...possible...Yes!

2004TR4-SR5

2004TR4-SR5

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i think i might have finally figured out the issue with my 4Runner regarding fuel mileage....after doing a ton of research all signs are point to the O2 sensor before the CAT....im not sure if anyone knows but the voltage for O2 sensors runs between .9 (rich) and .1 (lean) volts....this picture below describes a normal O2, rich, lean, and bad

<a href="http://s791.photobucket.com/albums/yy196/ToyotaSS/?action=view&current=o2chart_XIL_PakWheelscom.gif" target="_blank"><img src="http://i791.photobucket.com/albums/yy196/ToyotaSS/o2chart_XIL_PakWheelscom.gif" border="0" alt="Photobucket"></a>

I have a OBDII scan tool that can give me live readings and my O2's are not operating like a normal should be..i actually compared it to my O2's on my 01 Camaro SS and sure enough they are functioning normally like the picture shows.

Faulty MAF and O2 will completely F with your engine performance...Some people will disagree but these can be faulty and not send a code or light..that being said...im going to replace the MAF and the before the CAT O2's and i will come back with an update.

If you have any thoughts or opinions feel free to post
 
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A digital oscilloscope would be awesome to have in your situation.


Since you have a OBDII, can you get live voltage figures? '

I would believe that 1 of the sensors is bad and not throwing a code, but that BOTH a MAF and (a) o2 sensor are both bad, without some code? Odd.

Sometimes replace bits is about all you can do. Good luck.
 
well I'm definitely gonna start at the O2's...i think my scanner has a lot more things it can do that i just don't know of yet..hahaha but i just read in the manual about an O2 sensor test so I'm gonna try that tomorrow
 
If I rember correctly the o2 sensors are passive and do not adust the fuel mixture based of their results. So a bad o2 sensor will only report a fault, not adjust from it, and will have no impact on your mpgs.
 
Sungod said:
If I rember correctly the o2 sensors are passive and do not adust the fuel mixture based of their results. So a bad o2 sensor will only report a fault, not adjust from it, and will have no impact on your mpgs.
Click to expand...

Maybe the OP can chime in? Or is he enjoying the gain in MPGs after swapping out the sensors?

If it works I'm definitely changing all of them
 
knightsfs4 said:
I'm with ronsta, what's the verdict!!
Click to expand...

Word up... OP, if it didn't work no worries, we'll go back to square one... a lot of ppl are having this issue (whether they know it or not) and a fix like this would save ppl some $ not to mention the ozone layer ! :ybrick:
 
were you able to replace the a/f sensor? did it help the mpg? i have this same issue and figuring out how to replace the sensor. i have a v6, 4th gen model.

2004TR4-SR5 said:
i think i might have finally figured out the issue with my 4Runner regarding fuel mileage....after doing a ton of research all signs are point to the O2 sensor before the CAT....im not sure if anyone knows but the voltage for O2 sensors runs between .9 (rich) and .1 (lean) volts....this picture below describes a normal O2, rich, lean, and bad

<a href="http://s791.photobucket.com/albums/yy196/ToyotaSS/?action=view&current=o2chart_XIL_PakWheelscom.gif" target="_blank"><img src="http://i791.photobucket.com/albums/yy196/ToyotaSS/o2chart_XIL_PakWheelscom.gif" border="0" alt="Photobucket"></a>

I have a OBDII scan tool that can give me live readings and my O2's are not operating like a normal should be..i actually compared it to my O2's on my 01 Camaro SS and sure enough they are functioning normally like the picture shows.

Faulty MAF and O2 will completely F with your engine performance...Some people will disagree but these can be faulty and not send a code or light..that being said...im going to replace the MAF and the before the CAT O2's and i will come back with an update.

If you have any thoughts or opinions feel free to post
Click to expand...
 
thanks for confirming man. now i'm decided to change it. i already have the denso A/F sensor. problem is, was it easy? did you access it from top or bottom or the side? which tool to you suggest?

BOSMECH said:
I did my left bank sensors then I did my right side and my gas mileage went way up.
2003 V6 SR5
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