EARLY_S_MAN HELP!!! Need a MFI Transducer rescue

[Gearbox]

Hi, I have been following your posts on the subject of MFI problems and have found them extremely helpful, thank you. And after spending days reveiwing all the documentation and threads, I found that my RPM Transducer was the cause of a burpely backfire, afetr determining that the micro switch was working, the stop soleniod did kill the car at idle once 12v was directly connected, and the wiring was all good.

I took apart the RPM Transducer and tested all the components, and outside of a few broken soder joints, it was within spec. I took it to a electronics tech who fixed the soder joints and tested the board as well who also found it working.

Now here is the problem. Once installed, the lead from the Transducer to the micro switch shows about 1v at idle and a little over 3v at high RPM. Insufficient, I would think, for it to actuate the soleniod when the throttle is closed but RPM's are still above 1350, which is how I think it should work. I have voltage at poles 2 and 4 on the transducer, as well as good ground on pole 3 and good continuity from the micro switch at pole 1. Additionally, the tach is working so I assume the voltage I'm getting at pole 4 is a good signal ( how do, or should, I need to test this?). Also I noted that R10 reads 150 ohms as it is stripped, not 220 or 22 as in the digram.

So based on all this, is the transducer still at fault or is there something else I should be testing at this point? Thanks for your great posts and help, Allan

[304065]

Allan,

Warren will certainly weigh in. Until he does, here's my advice.

I- gray wire with red stripe. Power to microswitch. Power flows through microswitch. If throttle is at idle, microswitch contacts close, power flows through microswitch to solenoid, activating it, and to ground. With the engine RPM above 1500, you should have enough power to activate the solenoid, which I think is around +12v. If that's not happening, maybe the transistor that drives the output circuit is bad.

II. +12v from aft fuse box #2

III. Ground.

IV. Pulse from tachometer. As has been written here, the tacho pulse is an 11 volt square wave with 38 degrees of dwell. The best way to measure this is with a handheld scope, but a dwell meter will work OK.

The only difference between the speed switch and any other rpm-operated switch is the different trigger point for turning on and off. Remember: below 1300-- OFF, above 1500, ON.

[Grady Clay]

Allan,

Here is my annotated diagram. K1 (red box) is a relay. The box
labeled 100Ù is the coil, it controls (blue line) the switch
contact to the right. I suspect the contacts have deteriorated.
A possible cause is simply age and corrosion. Another is a failed
diode at the solenoid. If the diode has failed, it causes very high
voltage across the contacts when they open leading to failure of
the contacts.

You probably need to replace the relay (or at least repair the
contacts). You need to check the diode at the solenoid terminal
as in the other thread. If it has failed, replace it.




Best,
Grady

[Lorenfb]

The resistor values are wrong in the diagram.

Those units are available from Ottos Venice (310-399-3221).

[304065]

What are the right values, Loren?

[Lorenfb]

It's not 150 ohms. It's 150K ohms.
Also, diodes D7 and D8 are just 1N4001 clamp diodes.

[Otto]

We have those units in stock, rebuilt with a warrantee. $75.00 exchange plus shipping.