02 sensor question

I have a 92 tsi fwd and i was wondering how i could see if the 02 sensor is bad. I have a datalogger if it would help. thanks

The most obvious way would be a P0170 Fuel Trim Malfunction (Bank 1) CEL. But it could be dying and hasn't tripped the CEL yet. Is there a reason you suspect the O2 sensor to be bad?

Set up your logger to display O2 Sensor 1 (Bank 1), STFT, MTFT & LTFT add up to about zero, we are half way there. You should also see the O2 sensor bouncing up and down between ~0.2V and 0.80V everything should be fine. I would also make a WOT pull just to be sure. With a 1g, you should be pulling somewhere in the neighborhood of 0.88V at WOT.

It is using a lot of gas getting about 150 miles to a tank of gas. It is about the last thing to change that i can think of to get rid of the surge.. there is no leaks and i just replaced the coil, plugs, wires, timing belt, and some other stuff.

The voltage of the front 02 is 3.37 all the time.

that is way out of spec for the front o2....

What logger program are you using?

It sounds like you have it set on the wrong mode. I know some of the programs have settings for 3000GT's and a different setting for DSM. If I remember correctly, the 3000GT setting is the default, so you might want to check that.

If that's not the case, you could always probe the O2 sensor wire with a volt meter.

By surge, do you mean idle surge?

I am using mmcd v 1.5.. it is kinda old. yes it is idle surging. When i get the idle surge fixed i am going to get a dsm link.

ok i just sit there at an idle and i got a log from it and here it is

02-r 0.07v
tps 7.4
tima 20-30
02-f 3.37
cool 168.8 F
airt 88.6

ok i just sit there at an idle and i got a log from it and here it is

02-r 0.07v
tps 7.4
tima 20-30
02-f 3.37
cool 168.8 F
airt 88.6 F
baro 13.67psi
egrt -13.5 F
batt 14.6 V
isc 35.1%
ftrl 135.1%
ftrm 136.7%
ftrh 139.8%
ft02 100%


If this helps any

It looks like your front O2 sensor is shot, but it's hard to be sure because of the logger problems. Also, it's hard to tell because you are only giving me a snapshot of the system and not a log. We need to look at what the O2 sensor is doing over the period of, oh, let's say 60 seconds.

But, based on what I see, your FT's are all maxed out indicating the ECU is sensing a lean condition caused by a dead O2 sensor. I'm going to have to assume that what you have listed as "O2 r" is actually the front O2 and not the rear O2. If the rear O2 was dead, i.e. reading 0.07V all the time, you would be getting a P0420 Catalysist Efficiency Below Threshold, Bank 1 CEL.

So you don't have any CEL's? By the looks of your readings, you should either have a P0170 or a P0420 CEL. Was the car warmed up when you got those readings.

I would look into checking out one of the other free OBD-II loggers when you can.

Pick up a new OEM O2 sensor from www.sparkplugs.com since they are much cheaper than at the dealership if you decide to go that route.

EDIT -> I looked around and saw that when using MMCD, O2R is the front O2 voltage on a 4-cylinder and the rear O2 on a V6. O2F, is not used on a 4 cylinder and is the front O2 on a V6. So that clears things up. Set your logger up and take a look at O2R and see if it's bouncing up and down. If it stays around 0.07v, then we know for a fact that it's shot. I would put money on it being dead by looking at your FT's, but let's make sure before you start replacing parts.

After you get the O2 sensor installed, we can tackle that idle surge.

OK i got the 02 sensor installed it is new and it helped the surge at the time.. But after work i drove it home it is about 20 miles and when i got to my house it was surging again.. but when it was warming up it would idle kind of rough but stay steady between 1k and 1500 rpm.

tommorow i will look for some more leaks.. And see if it is not just a leak now..