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MG MGB GT V8 Factory Originals Technical - Throttle Position Sensor

Posted several months ago on drivability questions for the 1980 SD-1 Federal FI - I have some quiestions on the throttle potentiometer.

The voltage with the throttle closed is 3.9 VDC and very nearly zero with the throttle open. Does anyone have any specs on what this should be?

Thanks for your help.
Phil D

For the UK flapper type air flow meter, 290 +- 20 milivolts, throttle closed.
For the later hot wire it's 325+- 35 milivolts.
Geoff King


Thanks for your quick reply.

However, I'm still a bit confused.

The voltage shoud be the 290 MV when the throttle is closed, then increase as the throttle is opened?

Mine starts at 3.9 V and decreases. Am I reading the wrong sid of the resistor in the pot?

I did it the way it was suggested at the following website

Any light you can shed on the subject would be appreciated.

Phil Dooley
Phil D


The following is from the Rpi website and is supposed to apply to flapper and hot wire type systems.

There are three (3) wires coming from this unit to a multi plug. Do not disconnect. Wire colours are Red, Green, and Yellow. Red from volt meter to red wire of pot. Black wire from voltmeter to Green of pot. Volts should read .33 to .35

This is more or less the same info that you have but it doesn't say whether the volts increase or decresase as the throttle opens.

I don't know because my engine and the wiring is not finished but my guess is that it decreases to zero, (setting on 10V!! not higher - being the clue) and if it increased what would it increase to?

Geoff King

Throttle pot should read from low to high, with the high being usually just over 4v. Note that there are two visually identical throttle pots for mounting on different sides of the throttle housings, depending on the application. The operating arc of one is a mirror image of the other. I wonder if someone has supplied the wrong one for your set up and so your getting a mirror image reading.

Roger Parker

I sourced the fuel injection off of a running SD1, so I think I've got the right one.

I took it off to paint the housing and have alwawys wondered if I reinstalled it correctly.

My problem is that, according to RPIs website, that I'm reading the wrong two wires.

This thread was discussed between 18/11/2001 and 21/11/2001

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