Just to document what start up in a MAP system looks like, here's a little data log.

As you can see the MAP drops as the engine is spun by the starter and then it continues to drop as the engine first comes to life.

Now during a stall you can just read from bottom to top, and it looks about the same.

Run Mph Rpm KPa Tps CtsF MatF
00 0 0 91 0 63 63
00 0 0 90 0 63 63
00 0 0 87 0 63 63
00 0 0 86 0 63 63
00 0 0 84 0 63 63
00 0 0 76 0 63 63
00 0 750 73 0 63 63
Run Mph Rpm KPa Tps CtsF MatF
01 0 825 78 0 63 62
01 0 850 78 0 63 62
01 0 925 77 0 63 62
01 0 950 73 0 63 62
01 0 975 71 0 63 62
01 0 1025 67 0 63 62
01 0 1025 61 0 63 62
01 0 1075 57 0 63 62
01 0 1050 54 0 63 62
01 0 1100 53 0 63 62
01 0 1075 53 0 63 62
01 0 1075 52 0 63 62
01 0 1100 52 0 63 62

And when you dealing with the EPA, and worried about cold start emissions this is no minor issue. Hence some of the logic with going MAF, on the later cars.

 

im not goping to argue the logic. but the epa and the fed gov dicatated maf / s/d systems as well as sequential operation evac and a few thousand other thing. that is in the case of obd2.

 

The feds have never regulated any equipment. It was up to the manufacturers to meet the specification. ie there were cars that for years ran withour catalytic converters. GM does what seems to be most cost effective to meet those requirements. OBDII required the system to be able to fully diagnose itself with 2 seperate systems, one running in the back ground as a form of redundancy, and for better accuracy in diagnostics.
Since both systems are on the car there has to be some logic as to why the MAF is the primary one.

Anyone have any actual data to conflict with actual data logging?.

 

On the equipment, let me specify as relating to the engine. The restrictor in the fuel filler neck was mandated.

 

im not trying to be rude. you should spend some time rereading the actuall legislation. you would find that there ting where madnadate so int eh event of a fialure the car could retain decent emisions. do you think GM and all the other copany running MAf and S/D really wanted to spend the extra money ?

 

Which is cheaper?

The dual MAF and MAP OBDII or failing to meet CAFE requirements and the following fines?

 

So start a thread about that, I was posting about one aspect of things. One item that the MAP can't do as well as MAF.

I thought it was an interesting item, after seeing what was going on talking to a couple guys that work at an oem, and actually have to cope with the EPA daily. Kind of from the horses mouth rather then from conjecture, and speculation.

But again your off on a tangent about OBDII and this list is about 3rd gens..

 

belive it or not most likely paying the cafe fines.


as for starting strategy. well the pump down is an issue but one that some smart tunning can easily get around. even the maf has a crank afr. even though the MAF might see the air moving the engine still has to build enough cranking compresion to fire a charge. ive found the best way to do that is to lower the enable spark and fuel thresholds to lower rpm and fewer ref pulses. engine starts like magic every morning on the coldests days and the HC is well within even the newer obd2 2000+ standards without a cat.

The trick however is in realizing that you rarely if ever actually see a close to idle rpm and KPA of 100-110. so i use the region for my startup fueling. i also use the same region of the spark table in a different manner. at 100kpa and 600rpm i have 10btdc then as it approcahs the idle kpa of 55kpa its brings timing back in.

there are ways to deal with the startup strategy. Maf is most likely better for fueling however a map is much better for spark.

 

I was under the ASSumtion the ecm uses the code at startup not the maf.

 

It's always using the code.
There is code that takes care of cranking, to first run, ie under 400 RPM, and over 400 RPM. While it varies by calibration there is a point when the car is running on the ignition module and only after a given RPM is the EST line active. You can see in the rpm column that it's only as the engine burps to life that it suddenly reads 750, there is no rpm reading. While the engine is actually running the MAP signal is still pumping down from atmospheric. In the MAF world, you'd just see the airflow suddenly change.

Granted we're not talking a big deal, but when you building 10s and 100s of thousands of cars, it starts to add up.