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Model specific boards => Golf mk3 => Topic started by: Rmachines on 22 May 2011, 12:28

Title: A discussion about fuel injection systems
Post by: Rmachines on 22 May 2011, 12:28

I have a good understanding of modern SEFI systems but not so much about the old Mechanical and single point EFI.  Have a few questions..

First off,  obviously with multi point, the fuel cuts off when the throttle position sensor / Map sensor senses the throttle is close on deceleration, so no fuel is used when going down a hill for example..

Is this the case for single point?  The reason i ask is theres no reason why single point cant cut off, but all my single point engines past and present have backfired on over run,  why  is there unburnt fuel on decleration?

Seccond question,  Does Mechanical injection cut off on overun?  Bosch K jetronic for eg on the KR engines...   Its a mechanical metering unit, does it totally cut fuel on overun ?  Or does it drop to base idle settings?   Never looked into Kjet much.  ... again these also backfire on decel


Freel free to post other questions here too...  Im going through a "want to learn about Fuel injection phase)  :grin:

Title: Re: A discussion about fuel injection systems
Post by: javalin on 22 May 2011, 16:10

as far as I know the single point injection and multipoint injection works the same way, bar maybe some older cars...?  Its all about how the ECU was coded.

>Second question,  Does Mechanical injection cut off on overun?
not sure, but suspect it just reduces as no throttle applied.  was there mechanical petrol injection, thought that was just diesels?

James

Title: Re: A discussion about fuel injection systems
Post by: Rmachines on 23 May 2011, 11:03

The early ford xr3is and mk1 and 2 golf gti used bosch k jetronic which meters fuel using a flap that lifts up and down with air flow, there is no electronics although kl jetronic had electronic ignition i guess its not sequential so all four injectors must spray at once ?