Difference in Ref and Speed Sensors?

[dustinhu]

My '83 944 has both a reference and speed sensor (B and D). Does anyone know if these are interchangeable or are they actually different? The Porsche catalog seems to indicate they are the same part number. 944 606 115 00

I'm looking to buy a set which is why I'm asking so let me know if you are selling them as well.

Thanks,
Dustin

[TibetanT]

Dustin:

There is only one (1) part number because the sensors themselves are exactly the same.

However, their respective setup is precise so make sure the correct sensor end goes to the right harness connection for electrical signals to map correctly with the ECU/DME brain. If you car has the original sensors, and they still have the factory tape on them, each will have their respective label associated.

Hope this helps.

[Jeffm2815]

if these sensors are identical, can you switch the connectors to determine if one or the other is bad

[TibetanT]

Here is a picture of the sensors thanks to Porsche; all right reserved.

[TibetanT]

Originally Posted by Jeffm2815

if these sensors are identical, can you switch the connectors to determine if one or the other is bad

Jeff:

I would advise NOT to do this since each sensor has a respective duty in sending signals. You can however, swap their location as long as the harness cabling going to the "brain" is correct.

What I would advise, if you want to see which sensor is "bad" is to purchase a new sensor and then replace one sensor at a time, and then try and start the car.

Remember, each sensor MUST be associated with the correct harness cabling going to the ECU/DME brain.

My 944 still has the factory tape, BG/DG, labeling intact on both the harness side and the sensor side cabling.

Hope this helps.

[Jeffm2815]

If I unplug either sensor, the car will not start at all. I tried switching the connections, but this also results in the car not starting. Plug them back as they should be and the car will start and run for about 15 seconds and then shut down. If I try to restart immediately the car will not start, but if I wait about 5 minutes, it will start but dies after 15 seconds. I have replaced the DME relay and fuel pump, but still same results

[TibetanT]

Porsche labeled these sensors for a reason!

The reference sensor, closer to the block, is responsible for telling the "brain" when you are at TDC. The speed sensor is responsible for telling the "brain" how fast the flywheel is turning, which also regulates the fuel supply or rather fuel flow to the engine fuel rail.

It sounds like your speed sensor is gone. By swapping the connections, you may have now, also, fired a circuit/capacitor/resistor/diode inside the ECU/DME brain. Good luck with that.

[pfarah]

It might be easier to just replace both sensors, particularly if they're the same age. Alot less headaches in the future!

[dustinhu]

Thanks everyone. I'll replace them.

[944 Ecology]

Originally Posted by Jeffm2815

If I unplug either sensor, the car will not start at all. I tried switching the connections, but this also results in the car not starting. Plug them back as they should be and the car will start and run for about 15 seconds and then shut down. If I try to restart immediately the car will not start, but if I wait about 5 minutes, it will start but dies after 15 seconds. I have replaced the DME relay and fuel pump, but still same results

If your car starts and runs at all, then both sensors are working.

It almost sounds like the DME (ECU) is bad.

[944 Ecology]

Originally Posted by TibetanT

The speed sensor is responsible for telling the "brain" how fast the flywheel is turning, which also regulates the fuel supply or rather fuel flow to the engine fuel rail.

Actually, the speed sensor does neither. It provides just one of several inputs to the DME, which fires the injectors for an amount of time. The fuel supply and the fuel flow to the engine fuel rail are almost completely independent of the engine speed.

[TibetanT]

George:

I understand I made a slight error with my sentence, saying "it regulates fuel supply to the fuel rail" but the speed sensor does in fact transmit signals to the DME/ECU brain regarding the speed of the flywheel, correct?

This works like the Carrera 911 cars doesn't it?

Just trying to get some clarification as to why it is called a speed sensor since all my factory documentation suggests this.

[944 Ecology]

Originally Posted by TibetanT

George:

I understand I made a slight error with my sentence, saying "it regulates fuel supply to the fuel rail" but the speed sensor does in fact transmit signals to the DME/ECU brain regarding the speed of the flywheel, correct?

This works like the Carrera 911 cars doesn't it?

Just trying to get some clarification as to why it is called a speed sensor since all my factory documentation suggests this.

Yes, it provides speed pulses to the ECU, just like it does on the 84 to 88 911 Carrera cars.