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MG MGB GT V8 Factory Originals Technical - Speed transducer, HELP

I have a injected 3.9 with a LT 77 rover box. Is the speed transducer needed and how do I bypass it without messing up the computer. Any help in this area is appreciated.
Jimmy P

You don't need it, you can leave it out completely and the car will run. You loose some of your fine idle control, but it will barely be noticable. Make sure you have the correct 510 ohm resistor in line on your wiring harness. I believe it's between ground, and wire #34 in the ecu plug. You need this when running a manual gearbox.

Justin
Justin

I have speedometer "electronic". For set-up that, you know how much impulse by rotation in transducer.
Regards.
michel

And the big advantage is.....the ECU no longer restricts top speed to 115mph !!


Mike
Michael barnfather

The speed sensor fine tunes fuel provision while the car is moving - without it, the 108MPH restriction(for the RR)is removed as already mentioned, as is the compensation when you take your foot off at (say) lights or a turning. You may then experience a revs dip and occasionally a stall.

It's not very expensive to install in any terms.
RMW

Does anyone know how many pulses there are per cable revolution? I am going to lower gearing (3.27:1) and I might be able to trick the computer into thinking it's going 108 mph when it's really doing say... I dunno 120? Not that I need to go that fast, but the fine tuning on the idle control would be a nice thing to have. I have an electronic speedo with a VSS that gives me 2 pulses per cable revolution. As I turn the square end of the cable, the voltage at the vss goes from 0 volts, to 4 volts to 0 volts to 4 volts to 0 volts. That's 2 pulses of current for each full cable revolution.


Justin
Justin

many thanks justin
michel.
michel

Jimmy,
If you do eventually have a problem of sometimes stalling after bursts of high speed ,in cold weather(as I did), try resetting the base idle. You need to temperarally block off the stepper motor vaccum line while you do this, to stop the computer interfering.
The adjustment screw is on the plenum cover under a cap you need to prise out. Actually I'm not too sure whether it was the absence of the speed transducer, or the shortening of the plenum which caused this intermitant problem. Whatever the cause, since I made this adjustment its been perfect.
You know I still get a bit of a thrill every time I take this car for a drive.
Peter

I had a very pleasant call from Chris from RPI engineering the other day to tell me that it would be a good move to install the speed transducer. He says that the CPU looks for a signal from this sensor in order for it to come off the idle circuit and to help with engine braking and fuel control. I am looking for speed transducer Part # AMR 3386. If anyoe know where I can get a good deal on one of these, it will have a home.
Jimmy P.

Jimmy
let me know if you have difficulties your side
Roger
RMW

This thread was discussed between 19/02/2004 and 29/02/2004

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