Baro sensor questions

[seijirou]

Does anybody know the method by which a MAF equipped EEC-IV uses the Baro sensor signal to adjust the fuel delivery?

I've got a car that's running rich, and my MAF signal is reading 1.4 volts at idle, when it should be ~ 0.6 volts. With the key on, but the engine off, I have 1.09 volts. With the MAF unplugged I have about 2.45 volts. So the 2.45 is dropping to 1.09 when plugged in to the MAF, as would be expected because it is a resistor.

Talking this over, the question was brought up, is 2.45 volts higher than it should be? And what would cause this?

An idea came up that the computer may adjust it's base signal to the MAF depending on the signal from the Baro sensor.

An example of this theory, would be at sea level with denser air, the computer may step up the voltage to the MAF meter (say from 2 volts up to 2.5 volts) making it run richer across the board. At high altitude and low air density, the computer would drop the voltage to the MAF meter (say from 2 volts to 1.5 volts) therefore making it run leaner across the board.

This method would work, but I don't know that it's the way the EEC-IV does it.

Any takers?

 

[joel5.0]

MAF output passing range engine idling is .36 - 1.5 vdc.... BAP corrections are functions within the EEC, the MAF input is not affected by the BP..... IOW, all its calculations are done internal to the EEC not affecting the input portion in any way.....

 

[jrichker]

The baro sensor measures atmospheric pressure. It takes a reading when you crank up the engine. I am not sure of the interval that it samples the sensor input after the inital measurement.

As the atmospheric pressure decreases, the amount of fuel flow required decreases. This is because there is less air to mix with the fuel. To maintain the correct 14.7:1 air to fuel ratio, computer uses the baro sensor data to calculate a reduced injector pulse width.

An example of baro signal function is a hillclimb. Barometric pressure at the bottom of the hill is 29.92". At the top of the hill it is 28.5", a difference of 1.42". The computer sees the diffrence and reduces the amount of fuel delivered to keep the perfect 14.7:1 ratio.

Whatever the baro sensor does, it has no effect on the voltage output from the MAF.

There are three parts in a MAF: the heater, the sensor element and the amplifier. The heater heats the MAF sensor element causing the resistance to increase. The amplifier buffers the MAF output signal and has a resistor that is laser trimmed to provide an output range compatible with the computer's load tables. Changes in RPM causes the airflow to increase or decease, changing the voltage output.. The increase of air across the MAF sensor element causes it to cool, allowing more voltage to pass and telling the computer to increase the fuel flow. A decrease in airflow causes the MAF sensor element to get warmer, decreasing the voltage and reducing the fuel flow.

 

[seijirou]

Whatever the baro sensor does, it has no effect on the voltage output from the MAF.

I didn't think so.

So, without the MAF hooked up, what voltage should I be getting on pin 9 and 50 of the ecu?

 

[seijirou]

So, without the MAF hooked up, what voltage should I be getting on pin 9 and 50 of the ecu?

Nobody knows?

Measuring the volts at pin C and D of the plug with the MAF disconnected, key on, engine off, would be the same thing.

Could someone check theirs for me and let me know what they're reading?