Fuel Trims & O2v Questions

[StyleElements]

If any information is incorrect, please correct me.

Ok, to my understanding, fuel trims and O2v go hand in hand. First, the ECU reads information from the MAS, and calculates a good A/F ratio. THEN the O2v reads this ratio, and decides if it’s a little to rich, or a little to lean, makes its changes, and with that your STFT % is created. As I said in my other thread, my STFT is either 5, or 17, and LTFT is always 12, and they will not changed, regardless of where I set my SAFC. My O2v at WOT also will stay between .00 - .17. my guess, and everyone else’s, is a possible bad O2 sensor. Well my question’s are:

- Will the car still run with the O2 unhooked? If so, how will it act different?
- If the O2 is bad, how will this effect the fuel trims?
- Is to fine tune fuel trims the only reason the O2 sensor is there? if not, what else does it do?

I unplugged my O2, to see if it would change my trims, and the car acted EXACTLY the same, trims acted EXACTLY the same. Should this be an even bigger clue the O2 is bad? And why I cant change my trims? And maybe the car is just always running bad and I don’t know it? I’m sure you guys are tired of my threads but I have no one else to ask.

Thanks guys -

 

[spyderturbo007]

- Will the car still run with the O2 unhooked? If so, how will it act different?
- If the O2 is bad, how will this effect the fuel trims?
- Is to fine tune fuel trims the only reason the O2 sensor is there? if not, what else does it do?

Yes, the car will still run without an O2 sensor. The ECU will keep the car in "limp mode" which is basically designed to save the motor in the event that a critical sensor fails. Such as you O2 or MAS. Without an O2/MAS, etc the ECU has no way to properly calculate the correct amount of fuel to inject. It then drops back to a preprogramed factory default of sorts. It is a know amount of fuel that will keep the car running, but running very rich. This allows the owner to get the vehicle home, to a garage, etc.

Before the ECU begins to adjust FT's, certain conditions must be established. Car must be warmed up, you aren't trying to make power (WOT), excessive load on the motor, etc. If the O2 is bad (no voltage) the ECU will have no way to adjust FT's and will go into limp mode. If the O2 is providing consistently low voltage the ECU will try to adjust the air/fuel mixture using the FT's.....thus you positive FT's.

Yep, that's pretty much the only reason for the front O2. It really help with gas mileage. The rear O2 is there to verify catalyst efficiency.

 

[StyleElements]

Yes, the car will still run without an O2 sensor. The ECU will keep the car in "limp mode" which is basically designed to save the motor in the event that a critical sensor fails. Such as you O2 or MAS. Without an O2/MAS, etc the ECU has no way to properly calculate the correct amount of fuel to inject. It then drops back to a preprogramed factory default of sorts. It is a know amount of fuel that will keep the car running, but running very rich. This allows the owner to get the vehicle home, to a garage, etc.

Before the ECU begins to adjust FT's, certain conditions must be established. Car must be warmed up, you aren't trying to make power (WOT), excessive load on the motor, etc. If the O2 is bad (no voltage) the ECU will have no way to adjust FT's and will go into limp mode. If the O2 is providing consistently low voltage the ECU will try to adjust the air/fuel mixture using the FT's.....thus you positive FT's.

Yep, that's pretty much the only reason for the front O2. It really help with gas mileage. The rear O2 is there to verify catalyst efficiency.

thanks spyder, i bought a O2 from autozone today, sure does not look the same as OEM, its a bosche. the frickin wire is about a inch to short and i have to streach it accross the manifold. still have to make up my mind if im gonna try this or take it back

 

[BaddAssGst]

Definitely take it back, especially if you have to run the wire on the manifold. It will surely burn the wires and your back to square one. I don't know exactly how much you paid for it, but OEM is somewhere around 100 bucks, correct me if I'm wrong?

 

[spyderturbo007]

thanks spyder, i bought a O2 from autozone today, sure does not look the same as OEM, its a bosche. the frickin wire is about a inch to short and i have to streach it accross the manifold. still have to make up my mind if im gonna try this or take it back

I am with BadAssGst in that you should return it. Also, most aftermarket O2's don't have the O2 sensor heater. You can tell if it has 4 wires. If it doesn't have the heater, you will most likely get a DTC. Also, you will fail OBD-II emissions. Just go with OEM, probably just a couple dollars more.

 

[StyleElements]

yea it was a 4 wire, but its long gone. when i tried to slap it on .. the connector was nowhere near correct. i was going to splice it into my old connector, but all the wires were differant colors, so i was dead in the water. i got the o2 from autozone for 49$ it was a Bosch, that is the only o2 they have for my car. well i bit the bullet and orderd one from mopar, 80$ (originally 120$, i got connections) and if it has the right connector, will be installed tomorrow when i get it.

well when i took the old o2 out yesterday, the thing rattles really bad when you shake it. i guess even more reason to believe its bad. ill let you guys know if the new one fixes all my problems. thanks for the help guys

 

[Dred]

Hmm, I got the same probelm. At WOT for me it reads an almost flat 0, while at cruising seems to function somewhat as described in tuning/logging guides.

Keep us posted plz.

 

[StyleElements]

Hmm, I got the same probelm. At WOT for me it reads an almost flat 0, while at cruising seems to function somewhat as described in tuning/logging guides.

Keep us posted plz.

a new o2 sensor ended up fixing my problem prefectly