Hi,

I recently moved from Sea level to about 2200ft (650m) above sea level. I had the tuning done through Mazdamaniac a couple years back while I lived there and always had an idle around 14.7/14.8 AFR.

In my new location my idle is around 15-15.3 AFR, which is a bit lean and I'm unsure if this is within acceptable range or cause for concern.

When I am cruising my AFR is around 14.7 and my idle RPM is dead steady at 850ish. I have also put my CAT on the car (due to inspection) and the car was tuned with a test pipe.

I have two questions, and I'm sorry if this is the incorrect forum

1) is this idle too lean? Do I have something to worry about?

2) would this change be due to the elevation change or setup change or both?

Note: I have unhooked the battery so the car "relearns' but the AFR remains the same.


Thanks.

 

It should be 14.5-14.7 at idle. But it's not a big deal.

 

At idle your car is continuously adjusting the fuel delivery based on oxygen sensor result. So whatever AFR target it had before is still the AFR target it's trying to hit. Anyway, 15 is fine, at idle the engine is not stressed.

What is it a wide open throttle (before the move and after)?

 

If I recall correctly, a second gear pull it goes to about 11.2 +/-0.2, which I believe is close to what it also has been.

 

Reference your first post, your car will relearn if you disconnect the battery. The reason it still shows the same AFR is due to the short term fuel trim and long term fuel trim, your ecu will adjust on the fly VERY quickly to try meeting whatever AFR it's aiming for.. Now that AFR may not be what you would expect once you modify it, this is usually due to poor sensor calibration.

Also reference your last post ^^^, 11.2 is normal on a stock fuel map, you need to tune your car to lean that out if that's what you were expecting.

 

another fun thing to think about, is the barometer sensor in your car.. It should compensate for air density already either way so once again unless your sensors aren't calibrated correctly your car probably hit the same AFRs at your old location. Initially I thought about trying to tune all of my sensors but now that I study Geomatics Information Systems and Geospatial Engineering I realized that as long as your MAF and Injectors are tuned well the Baro sensor shouldn't make a difference, the stock tables are fine since you can't modify the atmospheric constants :P I assume Mazda was able to tune a sensor that doesn't rely on your cars dynamics fairly accurately.

 

I managed to do a couple first gear pulls this morning and was sitting around 12 AFR. Wasn't logging so I don't know the exact number so I do believe I am a bit leaner than the 11.2 stock map (I'm guessing higher is leaner).

I'm going to be putting my test pipe back on shortly so not sure if that will effect anything.

Is there anyway to tell if my O2 sensor is starting to get wonky and throwing off my readings? What would I look for?

 

I've never looked into sign of a dying o2 sensor... Google is your friend?

 

Hey guys, I've got an idle AFR or 20.7, would that be indicative of a vacuum leak?

 

HOLY CRAP!

Yes something is wrong.
Even with a vacuum leak your ECU should be trying to bring that back in to range.

Do you have a check engine light on? You should.

How are you getting this reading, what device are you using?
Are you sure you're really reading the AFR?

Other things
- Faulty Maf
- Faulty front O2 sensor
- As mentioned horrible vacuum leak

- Or you're just having a laugh with us.

Tell us about your car plz
Make, model, modifications, last maintenance performed

 

That sounds like a dead O2 sensor. Your engine won't idle at that AFR (it starts dying around 17:1), and the rear O2's check and balance would prevent that from actually being there. If you have a normal sounding idle, it's not actually running without fuel.

 

Did I miss something?
Do you have a link to the thread/information that proves this is the case with the rear 02?
I was still under the impression it was only for catalytic efficiency

Thanks

 

I don't know if something is messed up with my AP but after a pull as soon as I let off the gas the AFR goes to 20.7, when I'm on the gas it's usually near the 12-16 range. My car is a 2005, 130,000km and had a rebuild about 2500kms ago. The car idles fine and I have no problems starting it or keeping it running under idle at the 750rpm. I haven't done anything to the car since last year before I put it away for the winter, and that was only an oil change. Before that was installing a stock airbox instead of the k&n hot air intake I got with the car. I'll do a smog test when I get home and I'll take a log of a few pulls put it in Excel and post it up. I do have a BHR mid pipe I put on last year in May that has a leak where it mates to the cat back exhaust and I've heard that could usually throw out some bad numbers too.

 

Normal

 

Just found this video, sorry mine was going to 20.3 not 20.7. Thanks Brettus, just me being paranoid again.

 

that is the car undergoing fuel cut when you lift and the sensor hitting it's max reading. When the engine rpm actually falls to idle rpm it will level out at your IDLE AFR.

You might also see on the low end it will read 11.2 AFR When you are on the gas. There are some really rich spots on the stock fuel maps, but the sensor will not read any lower than low 11's.

 

Just put the AP down and drive the car.

Such questions clearly mean you need to invest in reading instead of gadgets