MFI engine hesitation when speed switch/RPM transducer connected

[SFE]

Since your original RPM switch worked fine in another car, I would suspect the problem in in your existing wiring, most likely the input signals (including the ground) to the RPM switch.

Well we did the test on a sportomatic car and we didn't let the car warmed up (it was inside a garage).
So maybe the symptoms were not present because the thermostat was not hot enough to lean the mixture.

Did another test today...if I disconnect the black/violet wire at the distributor the transducer don't work at all, which is normal I guess.
Then I have disconnected the same wire behind the Tach (PIA for the access...) and same behavior : engine stall at idle when the switch is depressed.
So I would say the Tach is not faulty...

[SFE]

Check my car with another CDI Unit today and same behavior...

I've checked all wiring again and everything is as per the 72 design.
Don't know where the 2 brown wires on pin 3 of the transducer are going but for sure they are grounded.

Here is my exact wiring, anything wrong with it ?

[tom1394racing]

The blue yellow wire from terminal two on your rpm transducer should lead to the stop solenoid. The diagram sketch doesn’t show that.

[SFE]

The blue yellow wire from terminal two on your rpm transducer should lead to the stop solenoid. The diagram sketch doesn’t show that.

Well, on the 69 diagram the Blue/Yellow wire goes to the rear fuse box :



On the 72 diagram the wire is not B/Y but Red /White and it goes also to the rear fuse box :



That's the gray/red wire which goes to the solenoid via the microswitch.

[tom1394racing]

The wire from the RPM transducer to the stop solenoid must be connected correctly or your test would not have shown the results you obtained when the engine shut off at higher RPM and the micro switch was engaged. Your problem seems to be a weak or intermittent output signal from the RPM transducer at idle speed. Testing your RPM transducer in a different car with a sportomatic when not fully warmed up should not have affected the results.

I would pull the RPM transducer out of the relay panel and wire some direct connections to the microswitch and a good known ground and try your tests again to see if anything changes.

[SFE]

I would pull the RPM transducer out of the relay panel and wire some direct connections to the microswitch and a good known ground and try your tests again to see if anything changes.

Well I guess there will be no RPM oscillation if the transducer is removed !

Anyway you propose me to remove the wire coming from the transducer to the switch and instead Connect a ground wire, then, press the switch ?
Is that correct ?

[edmayo]

Have you done the linkage adjustments and micro switch adjustments I mentioned earlier?

[tom1394racing]

To be clearer...I would pull the RPM transducer out of the relay panel and wire some direct connections to it. This would include all (4) wires to the RPM tranducer. A good known ground, a wire from the micoswitch, a wire to stop solenoid and the wire from the distributor. This, way you bypass any potential problem in the relay panel. Then try your tests again to see if anything changes.

[SFE]

Have you done the linkage adjustments and micro switch adjustments I mentioned earlier?

Of course Ed, with 2 different microswitch…

[SFE]

To be clearer...I would pull the RPM transducer out of the relay panel and wire some direct connections to it. This would include all (4) wires to the RPM tranducer. A good known ground, a wire from the micoswitch, a wire to stop solenoid and the wire from the distributor. This, way you bypass any potential problem in the relay panel. Then try your tests again to see if anything changes.

Now…crystal clear !!!