bleucamaro

I'm installing a piggyback computer (SMT7) on my 1989 944 S2 To be used down the road with a supercharger. To isolate problems, I installed the SMT7 first and the car is still normally aspirated. The car starts and runs fine. However, the SMT7 is not detecting a signal from the Hall Effect Sensor. I used pin 31 on the DME per the factory wiring diagrams, however the wire was white instead of the specified black. Is the diagram wrong on the pin designation, or do I have a faulty Hall sender? I also unplugged the Hall sender to see if the car would run without it plugged in, and it started and ran fine.

Is there any way to diagnose a faulty hall sender?
What is the hall sender used for?

Thanks in advance,
Dan.

bleucamaro

Well, my impatience got the better of me, I traced down all the leads, and the wiring is good. I stuck an ohmmeter on the sensor output and got an open circuit between H+ and H-, and 5-7 ohms between the H+ and HG, and between H- and HG with the car off. With the car running there was about 5ohms resistance between H+ and H-. I don't have an occiliscope, so I can't test it any further. Are these number resonable?

I also decided that I'll try to get a signal from the crank sensor instead (is this a better method?)

Bri Bro

Use the other wire coming from the Hall sensor; it also goes to diagnosis plug and this is a good place to look at it with a scope. If you disconnect the hall sensor (CAM TIMING) the car will run , very poorly, because the timing will always be retarded by 6 degrees. The car will still run because the speed reference sensor still supplies crank timing information to the DME.

The signal from the crank timing (missing tooth for timing mark) isn't a hall sensor. The voltage from this sensor starts out very small but increases with engine speed and this might damage the input to your SMT7.

bleucamaro

Thanks for the reply. The input for the hall is currently using a pullup so it can be read. I didn't use the other wire because it looked like a ground. I'll give it a try. Thanks.

Dilberto

All it is a Magnetic reference pickup, for RPMs

-Z

theedge

Does the SMT7 have VR (Variable Reluctance) sensor inputs? Even if it does, its dicey sharing VR sensors between two ECUs. I think the S2 uses the flywheel gear as its crank trigger, so if it does the SMT7 will need to be able to handle 132 pulses per RPM input as well.

How is the cam trigger setup on S2s? Does it trigger off each tooth on one of the wheels, or is there something else?