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Re: AMM Calibration[700/1989] posted by abe crombie on
Monday, 9 August 1999, at 5:39 p.m.
Volvo uses the same MAF sensor for turbo and non-turbo on 4 cylinders. They don't make it so hard. It's more a case of using a MAF sensor that falls into the needed CFM range. LH 1, 2 and 2.1 use the same #, LH 2.2 4 cyl use the same #, LH 2.2 6 cyl uses another # (it is a larger in diameter), LH 2.4 models use another #. The Motronic 1.8 inline six uses yet another #.
All but the 2.4 and M1.8 versions have the feedback potentiometer for trimming the baseline injector duration in idle program.
The listed ones above are all hot wire versions.
LH 3.1, 3.2, and Motronics 4.3 and 4.4 have the hot film version.
Re: AMM Calibration[700/1989] posted by Brad on
Monday, 9 August 1999, at 6:41 p.m.
Thanks Abe. This one does have the trim pot, but I guess I need a special tool to remove the plug with two holes in it ...or is that what I turn (to adjust) with the special tool??? BTW, it's definetely a hot-wire AMM. I've also got one from a N/A '87 Saab 900 which has the easy-to-adjust screw trim pot.
Specifically, what does the pot adjust? I presume there's only one voltage output to the PCM - does it just adjust the base-line voltage output? Wouldn't this also change the entire output curve?
If you (or anyone else) has any details on what the 6 circuits are and their associated inputs/outputs, that would be greatly appreciated.
Thanks!
--Brad
Re: AMM Calibration[700/1989] posted by abe crombie on
Monday, 9 August 1999, at 10:46 p.m.
That is supposed to be a tamper-evident plug. It is evident that it has been tampered with since it has holes in it for grasping it with a pair of needle nose pliers. It is smooth when new.
The screw adjusts a pot that moves varies a voltage signal, not the hot-wire mass sensing signal, to the PCM. This signal will change the base injector duration by some percentage to get the fuel mixture within the range that the oxygen sensor feedback correction (integrator function) can work. The idea is to get the base opening duration to a point where the integrator has the same range to richen and to lean fuel mixure to respond to signal from O2 sensor. The CO screw effectively compensates for MAF sensor in the range where it is least accurate, idle. The signal delivered to PCM only modifies the idle mixture. The MAF sensor signal is much more accurate above idle when mass of air passing is greater.