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Aisin Carby Alternative

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Have dissembled & cleaned this Mazda 121 EGi (Electronic Gasoline Injection), cross between a carby & a throttle body.  It appears to be made by Hitachi, including the TPS & MAF sensors.

Trying to discover it's design criteria, & how it works.  Unfortunately, I don't have access to a running Mazda 121, with an EGi "carby" fitted, which would provide a broader input, & something to play with, & take some measurements.

However, I was able to download a free Factory workshop Manual, that did throw light into where all those ofrifices going in & out of the dicast body.







The whole design is quite simple, & does, (as I hoped) lack the tiny little internal passages in the dicaste body, like our common Aisin carby, with it's idle, low, & main fuel jets & paths within, which can be so problematic.

The EGi unit, has a mechanical screw idle adjustment, with initial mechanical coolant temperature idle adjustment, when the engine is cold.  Once the engine warms up, the electronic bypass valve comes into play.  So the EGi is a mixture of olde world mechanical & new world electronic control.

The EGi is manufactured in two pieces.  The top casting includes the single injector & integral fuel rail. The bottom half is the throttle body proper.


Top half of the EGI, viewed from the bottom, clearly displaying the single injector discharge point, smack in the middle of the venturi.


Top view of the previous pic, The "fuel rail" passes straight across the casing, pressured fuel entering on the LHS, & the fuel pressure regulator, with return & atmospheric compensation on the RHS.  The MAF sensor fits to the flat on the bottom of this pic. The resistive elements are in the hole are in the airstream through the dished hole, which then swirls around, & re-enters the venturi above the butterfly, through two openings.


Same pic, but with the cover removed to show the injector snuggly fitted in the centre.


Top view of the throttle body.  The thermostatic idle control for cold engine is seen in the top RH corner of picture.


I want to take the injector out, to ultrasonically clean it, but have not been able to remove it, as yet. It appears that you push it back up, but it won't budge, & I don't want to apply any more pressure, in case I crack or break the dicast "bridge" across the venturi.   Suggestions welcome.

From Manual:


P.S.  Just got it out.  There are two (2) "O" rings supporting it, as I thought, but being old & hard, & stiff, they took a bit of budging.

Here are pics, with injector removed.





This is the cold engine idle control, which is disengaged, once the coolant reaches temp. Have measured it compressed length at room temp, then dropped it in a saucepan of hot water, withdrew it, & measured it again, to ensure it had expanded.  Works well.

One trick I found worked well, last night, while tracing the passage ways in the body, was to shine an LED pencil light into a hole, in a dark room, & then pier into the other holes, to see which ones were joined. There was enough reflection from the passageway walls, that you could see the light around bends & corners.

Cheers Banjo








Edited by Banjo

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