General Question on MAF, PE & WOT

[rushhour]

When a car is tuned for WOT during very hot weather, how does the car compensate during cold weather for WOT and the denser air (or does it)? Especially if you have reset the LTFT's preventing additional fuel add on to the PE EQ Ratio.

Basically, my WOT was dyno tuned during one of those nice 99 degree humid Jersey days (dyno was outside). Now we have winter.

The MAF is obviously picking up the denser air in its readings during winter. I assume (maybe wrong) that the hz reading is higher to identify a leaner condition. Yet the PE EQ Ratio curve is based on RPM's.

Is there an offset to compensate for the fact that the MAF hz were different during the hot weather at a specific RPM level that corresponds with the PE Ratio?

Or does the o2's supercede the MAF readings - if they report the demand AFR is hit based on the PE Ratio?

I noted on my tune both the stock & dyno tuned IAT adder are 0 all the across.

Should we have tunes set up for differnet air temps - say in 10 to 20 degree increments?

Sorry for what maybe a basic question - Just trying to get a handle on this.

Thanks

Steve

[animuL]

The whole point of a MAF sensor is that its very versatile for calculating airflow. As the air temperature changes the density changes and the MAF will read more or less air and adjust the injector pulse width accordingly. There are a lot of other little adjusters in the PCM that change things based on air temp, RPM, time in PE mode, etc.

You shouldn't have to change anything from cold weather to hot weather unless you are talking about maxing the MAF out.

The 02s are used to determine the fuel trim percentages needed to hit the commanded AFR. Basically the MAF reads the airflow and looks up how big the injectors are and what the AFR is supposed to be, then it calculates what the injector pulse width should be to achieve that AFR. Then your O2 sensors sample the exhaust and figure out how far off the actual AFR is from the commanded, then the PCM uses that info to set a fuel trim percentage.

If you remove the MAF and run on the MAP sensor then you will be more subject to the weather changing the tune, but with a MAF the weather shouldn't effect things much.

[5_Liter_Eater]

The colder air would cool off the MAF wires more/quicker than the hotter air so the different MAF Hz is not unusual. I would expect them to be higher so you may have hit some MAF Hz that you didnt' see when you tuned in the summer. Any Hz at or below the max Hz you saw in the summer dyno can be considered tuned. Which means your fuel trims should not change much from summer to winter. If you're seeing Hz above what you maxed out at when you got tuned in the summer those frequencies may not be calibrated although the function of the MAF is pretty predictable. Get them dialed in and you'll have a tune that will be good all year round.

O2's only come into play in closed loop. Once you're in open loop/PE they are ignored and the fueling is soley from the injector tables (IFR and offset)and airflow table(s) (EG: MAF). Thats why you need a WB tune so you can ensure that the numbers you have get you to your desired WOT AFR, the PCM is not using the O2's to correct fueling/airflow #'s when in open loop/PE.

[rushhour]

Thanks for the response guys.

I gives me a better understanding as to what happens during WOT and how it reacts to changes in weather.

Plus it gives me a handle on what the tuner went through to set the car up at WOT.

Until I get a wideband - I leave the tuning for WOT to others.

Steve