Going MAFless (SD mode) - Clarification needed

[dfe1]

I somewhat, kinda, almost agree with you, but I also somewhat, kinda almost disagree with you. The LS version of a MAF system does a lot of referencing and sanity checking. From what I've seen, it's actually a hybrid system that uses MAP and MAF readings in varying percentages. I don't know this for a fact, but I'm pretty sure that a lot of the sanity checking is included as a double check for electronic throttle control operation. The original GM MAF systems (1986-89) were pure MAF systems and no MAP sensor was included. LT1s also appear to use pure MAF systems with speed density being purely a back-up mode.

As with any air meter, eddies and reversion within the intake system can require application specific calibration-- that is, air may not flow the same way through a Corvete air filter/duct assembly as it does through a truck or F-body assembly. It would be interesting to check the accuracy of MAF air flow readings under controlled circumstances to see how much simply changing the filter/ducting altered MAF readings.

In spite of appearances, I'm not trying to make a big deal out of differences in terminology. I've just seen a lot of misinformation about MAF operation spread around and frankly, I'm not sure anyone (myself included) outside of a few GM engineers really knows how the system functions.

[John Skiba]

All measuring devices have "look up" tables or conversion tables. How does an temp sensor, oil pressure sensor, VSS sensor function? Some convert resistance values, some convert voltage values, some frequency. The MAF (Mass AirFlow Sensor) frequency output (LS1 at least) is converted in software (PCM) for flexibility of using the device in a wide range of application. One of the unknown variables as dfe1 mentioned which require the flexibility of a PCM lookup table being the air movement before and after the MAF due to ducting. If the manufacturer built the MAF with long tubes on each end to ensure consistant repeatable flow in all applications then it the output would be a fixed known. Such is not the case as the MAF is a small portable device which many times is placed before or after bends or in some cases right before a throttle body,etc.

Maybe we are all saying it in a slightly different way and I am missing something, but why would you not consider the MAF as a measuring device? Is it because it has a editable lookup table in the PCM?

[TAQuickness]

All measuring devices have "look up" tables or conversion tables. How does an temp sensor, oil pressure sensor, VSS sensor function? Some convert resistance values, some convert voltage values, some frequency. The MAF (Mass AirFlow Sensor) frequency output (LS1 at least) is converted in software (PCM) for flexibility of using the device in a wide range of application. One of the unknown variables as dfe1 mentioned which require the flexibility of a PCM lookup table being the air movement before and after the MAF due to ducting. If the manufacturer built the MAF with long tubes on each end to ensure consistant repeatable flow in all applications then it the output would be a fixed known. Such is not the case as the MAF is a small portable device which many times is placed before or after bends or in some cases right before a throttle body,etc.

Maybe we are all saying it in a slightly different way and I am missing something, but why would you not consider the MAF as a measuring device? Is it because it has a editable lookup table in the PCM?

The MAF is a measuring device, as is a MAP sensor. The PCM does not measure anything. PCM only looks up values. And I agree, if the MAF was installed with the proper plumbing, there wouldn't be much of an issue with the calibration tables.

I'm just splitting well split hairs

[John Skiba]