psychoideas

1976 911S 2.7 CIS
I was giving the car power today (12V) and I had the air cleaner and the Air sensor plate off and some slight smoke started coming from under the sensor plate.

There is a connection behind it with two wires.(brown and brown with black)
In my book, those wires attach to the "Air Meter contact"

What does this do?
and why is it hot?
Would it have anything to do with the fact that it hasn't been started for over 10 years???

Thanks

Droops83

This sounds like it is the airflow sensor, which senses if the sensor plate is moving. If the connector is plugged in, the fuel pump will only run if the sensor plate is moving, IE during startup and while the engine is running. If it is working properly, the fuel pump will not run if the key is in the "run" position with the engine off. This is for crash protection, so that the pump won't still be running if you get in a bad accident and the engine shuts off but they key is still on.

If the connector is disconnected, the pump will run all the time with the key on. This is for diagnostic purposes so you can check your system and control pressures w/ the CIS fuel gauge with the engine off, and also to check that the pump is working.

---Chris A.

psychoideas

Hi Chris,

Thank you for that.
I had the top hat off that joins the throttle body to the air flow meter. I also had the ait cleaner removed. So, I could see the top and the bottom of the sensor plate.

I was pumping the 10 litres of old fuel out of the tank so I could put new fuel in.
When I get the new fuel in I will purge the injectors. (got to hook up the accumulator first)

It was dark when I was pumping the fuel out and a mate of mine said he could see "light" coming from under the sensor plate. When I had a look it was like a collection of dust and oil was igniting. This was very small. It definately wasn't the classic 12v electrical arc.

When I felt the area it was warm. This "short" stopped when I moved the sensor plate up by hand.

Are there just two contacts there that join when the sensor plate sits down on them??

I guess I need a CIS injection manual.

psychoideas

Follow up.

I propped the sensor plate up and turned the key on.
Fuel pump is receiving 12volts. (pump not connected but I checked with a test light.
I went down back and let the sensor plate down to it's stop to see if the fuel pump would stop. I was going to go back up front and use the test light again.
I didn't get that far

When the sensor plate meets it's stop, it's arcs.
Also, when this arc is happening the whistle that the CDI unit makes changes it's pitch.

Where the F%&* do I start with this one???????????

art

If it has been sitting for 10 yrs, you are going to need to clean the fuel distributor, not to mention the rest of the fuel system. There are some sites that discuss the cleaning. The big thing is not to attempt to adjust or remove the little allen screws that are adjacent to each injector output on the FD. If you can clean without fooling with these, you should be in good shape.

One good test you can do is to prop the airflow sensor up a bit, put each injector into a cup/dish/bottle and turn on the pump. Look and see if they all relaese the same amount of fuel, and look at the spray pattern of each at some point. If they are even and have a good spray pattern you might be in reasonable shape to clean up whatveer else is going on and get running.

If you are propping the sensor plate without taking out the injectors, chances are you are flooding the engine badly. The sound change on the CDI unit (high pitch buzz) is probably due to the voltage change when the pump (tries?) to turn off/on. You can let the pump run all the time during this trouble shooting process, it is just a safety thing as mentioned above. Get the pressure guage at some point to really check what is going on with system/control pressure.