Newbie question, slightly off topic.

[Christian Hack]

> 
> I have been lurking around quite a while now, and though my
> own EFI project won't start seriously for another month or
> two I have a related question.
> 
> The scenario is this. I installed a anti-hijack/tracking unit
> in my car (Audi-EFI). The immobilizer relay (to disable the car 
> in event of an hijack) is connected in series with the booster
> pumps' fuse, ie when the car is immobilized the main fuel pump 
> will run dry.
> 
> When this happens what damage will be caused to the engine systems?
> I'm quite willing to accept an amount of damage in return for recovering
> my car, and the immobilizer will only be actived with my constent,
> but knowing what will break would be nice.... ;-)
> 

Well I can tell you that standard procedure for my car (an Australian VL
Commodore with a Nissan engine) for depressurizing the fuel system is to idle
the engine and pull out the fuel pump fuse. You then attempt to start the engine
a few times to ensure all the pressure in the fuel system is gone.
On my car it stutters and stalls after around 3 seconds and then is quite difficult
to even start

In a high load situation, not too much damage would occur I would guess. At worst,
the engine will run lean (as the fuel pressure drops) for a second or so. Remember
that under load a lot more fuel is injected than at idle

The other thing that maybe of concern is running the main fuel pump dry. Some
pumps rely on the fuel in order to cool them. Running them for too long dry could
stuff things.

> Does anyone know whether the fuel pump is switched off immediately when the
> engine dies of fuel starvation?
> 

In my car the ECU turns off the fuel pump essentially immediately the engine
stops/stalls. It will turn the pump back on if/when the engine is cranking again.

> Regards,
> Nic van der Walt
> South Africa
> 

Christian Hack
DESIGN ENGINEER
christianh at edmi.com.au
EDMI Pty Ltd
Ph : (07) 3888 3066
FAX : (07) 3888 3583