Help Identify Sensors...

[motogman]

I am working on my 81 SC stock 3.0L engine and as I learn about the CIS system I have some questions I have not found direct answers to...

What is the sensor (green plug connector) on the air flow module and how is it used in the fuel control strategy (assuming it is for that purpose)?





In this picture there are two sensors - one mounted in the case (red) which I think is the oil pressure light switch - is this correct?

The other, mounted in the breather cover - what is this sensor and what does it do - how used in system?

[patz]

Air flow, I believe.

[ossiblue]

Green plug is air flow sensor. It sends a ground connection to the fuel pump relay when there is no air flow through the intake causing the relay to switch power for the pump to the starting circuit. As soon as air flows, the sensor breaks the ground connection, the relay de-energizes, and switches power for the pump to the ignition "on" circuit. It is a safety device that kills the pump if the engine stalls with the ignition in the "on" position--like in an accident.

[jrbennett]

As per ossiblue, the green two pin connector is for the air flow sensor contact.
Red sensor/switch is for the oil pressure light.
The other senosr in the breather is a temperature sensor for the lamda control unit (oxygen sensor control)

[OsoMoore]

Originally Posted by ossiblue

Green plug is air flow sensor. It sends a ground connection to the fuel pump relay when there is no air flow through the intake causing the relay to switch power for the pump to the starting circuit. As soon as air flows, the sensor breaks the ground connection, the relay de-energizes, and switches power for the pump to the ignition "on" circuit. It is a safety device that kills the pump if the engine stalls with the ignition in the "on" position--like in an accident.

There is a second nearly identical wire/connector which is sometimes confused with this one. The Cold Start Valve sprays gas into the airbox at startup, and its wire can be inadvertently swapped with the air flow sensor wire.

The car will still start (at least in warm weather) but will be unsafe because the FP will keep running when the key is On but engine isn't running. For example, in an accident you could spray gas everywhere. And you won't get the desired fuel spray in the airbox to aid starting.

911 CIS Primer - CIS Lambda has an excellent overview of how the whole system works. These CIS setups are a balance of fuel pressure, air pressure, cleverly positioned weights, and a few heating elements. It is amazing what they did with almost no electronics (other than CDI box).

We have lots of CIS experts floating around here on PP, but the system can take a while to learn. Good luck!