I noticed o2 sensor wire is disconnected on my 1991 T2 with full racing beat exhaust and 255 fuel pump.
My question is, which no concern to emission, is there a point to repair/replace the o2 sensor? and why?


Thanks!

 

the O2 sensor really only gets used at part throttle, ~1500rpm to about 3500, so if you put it back in, you'd probably get better mileage. emissions would be lower too, but if you don't have a cat it wouldn't be very noticeable
the o2 sensor is there to correct the mixture so the Catalytic Converter is working as close to peak efficiency as possible as much as possible.

 

I remember back around 2015, taking my '90 GXL in for its final emissions inspection. I too live in VA and after 25 years emissions inspections are no longer required. During the test, a couple techs were looking closely at something on the right side of the engine. I passed the emissions test and that was all I was concerned about at the time. The next time I went to work on the car, I noticed that my O2 sensor wire was broken off at the harness and was completely missing. So, I spliced in a new temporary wire from harness to O2 sensor. After that, my gas mileage improved considerably and I got better throttle response.

The ECU only uses O2 sensor feedback when the car is running in closed loop mode. The ECU should give an error code if the O2 sensor isn't functioning. Running in closed loop improves your car's gas mileages and performance due to leaner running. Running in open loop mode will not really hurt your car or anything. If you search the forum, you can find lots of discussion on this subject.

 

It helps you get better emmissions. That includes the long term (not breaking your main cat).

I would go broadband in the long term to find isues with running to lean / fat.

 

I was thinking wide band but I'm unfamiliar if that be read by a stock ecu, I would like to see the visual but does the ECU even detect it?

fyi, I have a rtek 1.7, full racing beat exhaust (from head to tail piple, no cats), 255 fuel pump, ported turbo

 

You “should” run a wideband sensor to actually see what the afr’s are.

long story short, I loaned my wideband to a buddy for a few months. I get it back and plug it into my fc and it shows I’m running lean everywhere. I use the apexi safc to add fuel, same lean conditions. Turns out the fuel filter was clogged. New fuel filter, afr’s went back to perfect.

I consider running a wideband a must to see if there are any anomalies.

and the stock ecu only reads the narrowband. And no I don’t recommend running an aftermarket narrowband afr gauge, pony up the money for at least an AEM Iego or better.

 

Can I use apexi safc to adjust fuel with rtek1.7?

 

Yes, you should read through my posts on it. I also think Stussy did it. We both did it on s4’s but will work on s5 too, and actually ran the input to the safc from the boost pressure sensor instead of the tps so we could add fuel based on boost pressure, not the throttle pedal. It was a common modification on the DSM forums.

Both methods work, but the boost sensor input works better. Plus on s4, tps only reads up to 30%, everything more than that the safc would think it’s 100% WOT.

also should read up on apexi’s ignition control device everyone forgot about. I bring this up because the safc modifies the afm signal which can affect timing if you go adding or removing close to the +-50%. Minor fuel adjustments won’t make a difference.