Accuracy of GM MAF and MAFT

[Kmiller86]

Hi, I have dsmlink and use its calculated a/f ratio since i dont have a wideband yet. My question is, if the maft isnt callibrated perfectly, would the calculated a/f ratios be off? Also how do you know that the MAFT is reading right. THanks

 

[LousyDriver]

You've just put your finger on the reason people need wideband.

The answer, I suspect you already know, is that the calculated airflow IS off, and there is no way to calibrate it.

There are two ways to get air/fuel ratio with the information the ECU has. One is to divied the airflow by the pulse width of the injectors, and use a calibration constant to convert that ratio to air/fuel ratio. The problem is, that the airflow isn't accurate. The pulse width is pretty good, as long as the fuel pressure is constant, the amount of fuel injected should be known pretty well, but there is no way to calibrate the air sensor. (short of sending it to someone who could measure the flow - this would probably cost a lot)

The other way to get a/f ratio is to look at the narrow band o2 sensor. However, at any ratio other than stochiometric, this is even worse than the first method. You could sort of combine the two and try to come up with a good average - this is what the ECU does when it adjusts your fuel trims, but it still isn't nearly as accurate as a wideband.

So, when you get a wideband, let me know. I'd like to borrow it.

 

[Kmiller86]

Thanks. I will be looking into getting a wideband in the next couple weeks. After i get my new clutch, shep tranny, and driveshaft shop axles.

 

[tstkl]

<-(NEWB)

where can you get wideband, how much, what exactly is it/where does it go?

 

[LousyDriver]

Wideband is a more accurate version of the oxegen sensor in the cars exhaust stream. They run around $350 on up, but are probably most useful if you get one that logs air/fuel ratio along with rpm, so figure about $450 for a proper setup.

The stock oxegen sensor only lets you know if you are rich or lean. Without wideband, tuning your car is a long process of carefully reducing fuel until you get a little knock at certain rpm, then richening up that rpm band, over and over until you have a proper tune.

With wideband, you can go make a run, then read your air-fuel ratio over the entire rpm range, and dial your fuel tune in precisely.

It installs just like the stock O2 sensor, although most people put it further down the exhaust stream. Some will generate a narrowband o2 signal so you can remove the stock o2 sensor completely.

The alternative is to go to a dyno and use their wideband, I'm not sure how much a dyno run would cost you. The downside is you have to go back if you change enough stuff.

The vendor forums would be a good place to locate a wideband and compare prices.

 

[tstkl]

ok so i did some research, and i came to the conclusion that the aem wideband gauge uego thingy would be the best, because it seems like aem makes quality parts and stuff, (newb decition, but whatever) then i realised, how do i tell if the a/f ratio and rpm can be logged? i mean this looks like its just an o2 sensor replacement, and a gauge... could i hook a datalogger up to it and have the info saved on that?