I just checked my ecu and it says my rear 02 is out will that make my exhaust smoke a lil or is it something else?

 

When those go bad it richins ur car, what color is the smoke coming out?

 

shouldn't do very much since it only monitors your cats status...

your performance won't degrade... change it when you have time no biggie...

mines been bad for about 6 months now... :-/

 

it's like light grey

 

Its does degrade ur performance, I don't know what u are talking about.

 

ur are running rich, fix the o2 sensor then check for smoke, it should be gone.

 

Thanks i'll do it this weekend.

 

what do you mean by running rich

 

O2 sensors do mess up your performance and gas mileage. If the 02 is bad then the exhaust coming through the cat will not be read corectly and the ECU will have to adjust making you run ruch...

 

my rear o2 on my cat is comeing on 2. is these do 2 my test pipe i have a 96 maixma.

 

Only the front 2 O2 sensors affect the A/F. The rear only monitors the catalytic converter efficacy on OBD equiped vehicles.

 

sooooooooooooo running rich means i burn more gas?

 

hey...its just like my car.i got the 0304 code but people tells me it could be my O2 sensors tripping my KS.and just like stonemaxs,my car gives off smoke everytime i drive it and its light gray.the performance has degraded, fuel economy is down to 17/gallon until i put in my intake;and now im gettin like 18-19/gallon.now my problem is,i cant really make a good decision whether to replace my O2 sensors or my KS instead.nissan dealerships charges 77 dollars for determining which sensors are bad.we would appreciate comments and suggestions.sorta like hitting 2 birds and one stone for you guys.

 

Yes, running rich means burning more gas. WHich one is your car giving a code for the o2 or KS??

 

One of the roles of the ECU is to manage your fuel and oxygen mixture. It does so by reading the mixture levels from the O2 sensors. When your O2 sensors malfunction (and we have the good fortune of having three) the computer switches to a default setting and switches the mixture to rich. This setting will allow the car to operate and not stall. A rich mixture will cut into your fuel economy for the sake of functionality. This is basically the explanation for why one would get better fuel economy with a working o2. O2's arent very expensive and are worth getting replaced. I had the pleasure of replacing all three over the past three years.

 

im actually getting a code for the kncok sensor but the KS could be tripped by the O2 sensor from what i understand.now...my question is...how can i tell which sensor(O2 or KS)is actually causing the 0304(KS)code?

 

If you pull the codes and more than one code shows up including the KS, then fix the other problem(s) before the KS. After you fix the other problem(s) then reset the ECU and after a few days check for the KS ghost code.

If you pull the codes and only 1 code shows up (the KS ghost code - 0304) then the KS is dead.

 

hmmm...is that so.coz im only getting the KS code.i reset my ecu and after driving for quite some time,i try to diagnose it again and its back.i would actually go for the KS replacement but D A M N! what if its actually my O2's?then thats like spending more than i had to to fix one problem.

 

I think that the KS code isn't fired with the rear o2 sensor though... i read that here somewhere....

my rear o2 was firing along with my KS...

I checked my KS and sure enough it was measuring 0 ohms... and it was cracked... so i replaced it and still have a rear o2 code, but i have all my power back atleast feel like an increase of about 18-20hp.... or the addition of a ypipe + a couple horsepower... so maybe between 14-20hp i guess?

 

What Chunger says is correct. Only the front two O2 sensors are used to monitor afr. The rear O2 sensor (i.e. the one behind the cat) is used only to monitor the cat and has no effect on closed loop performance.

 

I can back that too. I put in an aftermarket Y and test pipe in place of the cat without resetting the ECU. The computer and rear o2 sensor caught this and the SES light came on. The code it kicked up was a 702 3 way catalyst malfunction detected by the rear o2 sensor. Reset the computer and and the code has been gone ever since.

 

im just gonna leave the rear O2 sensor alone.i just ordered 2 O2 sensors at www.buyoxygensensors.com. its like $63 a piece.i dunno if its gonna be good but its made by walker i believe.oh well,if that doesnt fix it then i guess ill have to fork out more $$$.either way..its all for the good

 

i bought one from them and it runs fine so far... been about 5 months i guess?


I say check your knock sensor manually... pull it out and check the resistance... let us know... it's a 30 minute job... ~about

 

Why waste 30 minutes on taking it out, he might as well put in a new one. Just disconnect it from the harness and check it with an ohm meter. Negative lead goes to the negative battery terminal and positive goes to pin 2 on the harness. Checking the resistance won't do anything since A BAD KS WILL MOST LIKELY GIVE SAME READING AS A GOOD ONE. Just disconnect it from the harness and see if the car drives worse, if not then you need a KS...

 

What I was saying was that if you pull the codes and only the KS code is there, then the KS is bad.

If you get a CEL and pull the codes, you'll get 2 or more codes. Fix the other problem(s) first then reset the ECU. If the KS comes back by itself, then it's bad.

Since you pulled the codes and it's only the KS code, then your KS is bad. Lets PRETEND you pulled the codes and it came up with the O2 and KS. Then you would replace the O2 first and see if the KS code comes back.

 

This is very weird since a KS almost never comes on by itself. Usually you have to check the ECU for codes and if it shows up after resetting it will disappear for a few weeks...

 

thats the same thing that i was told by some dude that i know.biut hes still leaning towards the "the O2 might be tripping it" idea.i really dont mind spending the $ over this because i believe its almost time for them to be replaced anyway.it has 95K miles so i would think that im actually doing my car a big favor.thanks for all your inputs though.

 

bah it's the rear o2 though... it ain't as bad if you wait...

it's the knock sensor which is most important...

I'd do like above and check using the harness... it's another method of checking it Only thing is that i remember hearing here somewhere something about the measurements being a bit different when measuring through the harness as opposed to on the actual sensor...

something about the measurements being half what the actuall KS reading is sending back... I dunno. It's something i remember reading :dunno: