Some questions with the '81 CAS and MSnS-extra

[Metro]

I can't seem to get a RPM signal with a '81 CAS, MSnS-extra and a v3 board. Also, when I have the ecu hooked up in the car with megatune, the RPM and PWM guages are white until the fuel pump shuts off, then they go red as if they're not connected. They don't turn white again unless turn the key to off and back to run, I'm not sure if that's normal or what.

 

The car isn't fully wired up yet, so I'm not checking for spark or anything right now. I just want to see that the CAS is working with my setup.

 

First off, I want to make sure I have the CAS wired up correctly.

BW - 12volts (using the original wire for the coil to power it temporarily)

GB - wired with a 1K resistor wired to tach (#24 on the DB37)

B - ground

GY - not used

 

If I hook up a multimeter to GB, should I see some sort of signal? As it stands now, I don't see anything that looks like it could be a usable signal to the ecu. My car was having all sorts of weird problems before I decided to run MS (bad I idea, I know..) and I sort of suspected the CAS might be bad.

 

Well, if that's all good, my next question has to do with the v3 board setup. I have it jumpered to use a hall/optical/points input. The other option is VR, which I can't see why I should enable that input. As far as I can tell the 81 CAS is a hall sensor with a transistor to modulate the reference voltage, which is why the optical 82-83 can be used with different ecus. I've read a few posts by Phyxius that the wiring is the same, so unless I have it wired wrong, I'm thinking the CAS is defective.

 

If nobody can come up with anything, I think I might just go ahead and use my 76's VR distributor with the built in VR conditioner that comes with the v3 board.

[mobythevan]

If nobody can come up with anything, I think I might just go ahead and use my 76's VR distributor with the built in VR conditioner that comes with the v3 board.

 

I think that would be a good way to go. Weld it up solid to get rid of vacuum advance. And take your time phasing the cap and rotor so during high advance the spark doesn't jump posts and you should be good.

[Phyxius]

Are you using a frequency counting multi-meter to test for a signal? If you are just looking for some voltage coming out of the wire when the trigger passes, it may not register. You may try using a small light bulb or LED to see if it lights (or turns off...depending on the sigal...i can't remember at the moment which it would do) when the trigger points pass the sensor.

[Metro]

I went back and hooked up my Fluke 87 DMM and still didn't get anything. I tried DC, AC, and Hz, nothing. I also tried wiring a LED to it like you suggested, but again nothing. I never did like the CAS, so I'm already in the process of tearing apart my 76 dizzy to fix the mechanical advance. Looks like it will be fairly simple to adapt.

[Tony D]

An O-Scope tells all on them!

The pulsewidth waveform from the 81 CAS is identical to the one from the later CAS unit in the Dizzy area.

 

Wire power from the battery to the wire with 12V---make sure you have good power there.

Then make sure your pullup resistor is connected good---mine fell out causing some bad stuff. You should get a cranking RPM signal if there is a pulse coming out of the CAS.

[Metro]

I really didn't want to mess with the CAS anymore so I welded up the mechanical advance on my 76 dizzy and used the VR inputs. Works great so far, I have a rpm signal and I get spark from the VB921 as well. Haven't worked on it much past that.