MFI speed switch and CDI
 

I am doing some tuning on my transplanted MFI 2.4E engine. It is running well except for the MFI fuel overrun solenoid circuit. As best I can determine the >1300 RPM relay is never getting energized in the RPM transducer (speed switch) box and thus not putting out 12v to the microswitch. All the connections in the solenoid circuit seem to be correct.

The speed switch was recently rebuilt by Otto's and I believe it to be good. My suspicion is that the Bosch CDI I'm using (a late 3 pin -- part number 0227 200 008) is the problem. I've read here that the 008s had a different pullup resistor than the earlier CDI units and people had tachometer compatibility issues.

If this is the problem, can the transducer be modified? Has anyone done it?

My tachometer is working fine, but when I had North Hollywood restore it, they asked for the CDI part number, so they likely took care of any necessary compatibility change.

Thanks!

Disconnect the CDI module and measure the resistance between the center pin (B) and pin (C) trigger. It is either 30 Ohm (early box) ior 100 Ohm (later box). If it turns out to be the later 100 Ohm version you can simply add another resistor between the distributor output and switched +12V. This will make the CDI appear equivalent to an early box version. The value of the resistor should be 50 Ohm and 5W.

Ingo

"I've read here that the 008s had a different pullup resistor than the earlier CDI units and people had tachometer compatibility issues."

The CDI type being used should not be the problem, as all that the speed relay
needs is a voltage greater than 5 volts when the points open to trigger the relay.

The CDI is the late pullup, but as per Loren, it doesn't matter. So, I spent a couple of hours going back over it this afternoon -- reflowed a couple of suspect solder joints, cleaned the contacts and tightened up the harness side connectors and it worked.

Thanks all!