So I'm trying to diagnose bad MPG, and exhaust smell. I bought an air/fuel gauge to help me figure out if I'm running rich. Only problem is, I'm not really sure what it's telling me because of how much it jumps. So, I made 3 vids, one @ idle, one @ city speeds, and one @ highway speeds. Can you tell me what you see? I got rpms, the gauge, and speed (the big green number by the HVAC) in each vid.

Idle:
City:
Highway:
Thanks, I appreciate the help.

 

Sorry I can't help you there it's all over the place. I find nothing useful, I suspect bad gauge or sender.

 

Ideally a completely stock Naturally aspirated engine should ideally run at 14.7:1 through out all ranges. If it was running around 10:1 it would be really rich and 15:1 would be very lean.. If you are getting bad fuel mileage, you might want to find someone who knows how to test you O2 sensor.. The computer looks at alot of different items to adjust fuel..

 

The gauge I got was just a cheapo off the shelf at Autozone. It's here: http://www.autozone.com/autozone/acc...er=872187_0_0_ and it just splices into the O2 sensor before the computer. Brand new sensor as well.

I've spent a lot of time with this engine, and the only things I can think of that are left, is my MAF sensor, computer, or o2. When I plugged in the current o2, the smell went away for a couple trips, now it's back. Money is tight, and I'm putting off visiting a mechanic until the last second. That's why I bought the gauge. I just don't understand how I'm supposed to read what it's doing.

 

I've only seen one A/F meter in operation and it sure wasn't doing what yours is doing.

I think it would be more useful to hook up a scan tool to the data link and figure it out that way instead of an air/fuel meter. Of course, you'll need to find a scan tool......

 

That is totally normal, it is the o2 sensor switching. If you were to use a multi-meter to check the o2 output voltage you would see the voltage jumping up and down. If your car had a carburetor it would be steady.

 

What does it do at wide open throttle? Does it stay full rich or does it continue to jump? At WOT it should display full rich as it runs in open loop and the car runs around 12:1 AFR. Cruising it will want to be around 14.7:1 so it will jump from lean to rich. Only if you had a wide band 02 sensor would you be able to read actual AFRs.

 

Narrow band sensors are very hard to get accurate readings. If you see the lambda curve of a narrow band, you'll see what I mean. There's a nice gradual slope as it climbs in the rich scale then suddenly it drops off as lean. In that sharp drop off is where the 14.7:1 ratio is and a narrow band will jump all over the place as it moves up or down from that one point.

It's much better to use a wideband sensor.

As mentioned above, see what kind of reading you get at WOT. Partially driving around, the engine will always try to compensate to get a perfect AF mixture. Judging my your meter, as long as it's not pinned over on one side or the other, it's probably fine since it's constantly trying to adjust At WOT though, the engine needs to be rich to make the most power.

On an AF gasoline scale at WOT, the mixture should be in the 12.8 - 11.9 range. Any lower than that and it's running too fat. Any higher than that at WOT and it's starting to run lean.

I use a wideband for datalogging in my race car. Even at an idle I get a stable reading.

If there's a way to change the sample rate, the meter may stabilize.