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'[PICLIST] [OT] Any ideas on a car security system'
2001\01\28@030715 by John De Villiers

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> Does anyone have any sound hypothesis (or better yet - real world
> knowledge) about what happens when the fuel line to the injectors is
> depressurized, as far as damage to the car?  (obviously it won't run well,
> if it runs at all)
As far as damage goes i dont think there is much that can go wrong. The fuel
pump pumps like mad to keep the pressure in the injector bar up at whatever
level it needs. It has a preasure bleedoff so that when the bar is at the
desired pressure the fuel is just pumped back into the tank.

Letting it run dry is a big fubar as you now have to bleed all the injectors
to get the air out. NOT A FUN EXCERSIE.


Regards
John

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2001\01\28@040700 by Lee Jones

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>> Does anyone have any sound hypothesis (or better yet - real
>> world knowledge) about what happens when the fuel line to
>> the injectors is depressurized, as far as damage to the car?
>> (obviously it won't run well, if it runs at all)

The controller will try to compensate for low injector
manifold pressure by increasing the injector pulse widths.
If the mixture in the cylinders is lean enough, you can get
hot spots and knocking -- which should trigger the knock
sensor and cause an engine shutdown.  Usually, if the fuel
pressure is varying sufficiently, the engine just won't run.

Continuing to attempt to operate it without fuel can cause
localized component overheating.  Some of the pieces rely
on the fuel carrying away heat.  But you'd really have to
go to extremes of cranking it without fuel.

Cars are robust.  They have to be because most people don't
think about how they operate them.  And consider the range
of ambient temperatures considered "normal".  If a car were
fragile, the manufacturer would have a bunch of unhappy
customers and would soon be out of business.


> Letting it run dry is a big fubar as you now have to bleed all
> the injectors to get the air out. NOT A FUN EXCERSIE.

I disagree with this.

How do you "bleed an injector"?  To bleed a system, you
pressurize it then provide an opening (i.e. unseal the
system) which allows the fluid to force out the entrained
air.  During cranking, the engine control computer pulses
each injector several times per second.  The open injector
acts like a bleed valve.  So "bleeding" is automatic.

If the system runs dry (i.e. out of fuel condition), the
pump will obviously run out of liquid.  Once the tank is
refilled, the pump will usually begin pumping again.  A
lot of pumps are inside the tank, so they are submerged
with a full tank of fuel -- an easy prime.

The fuel pump supplies a higher pressure than the engine
needs.  The regulator lowers that pressure to the desired
value by bleeding fuel from the injector manifold back to
the tank.  Any air in the injector system will be forced
out by the much higher pressure fuel.

Air in the injector manifold happens frequently during
maintenance.  If you pull the injector manifold off, the
fuel drains out (all over your hands, usually).  After
reassembly, the first couple seconds of fuel pump operation
repressurizes the entire system and the engine runs fine
right away.  At least that's the experiences I've had.

                                               Lee Jones

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2001\01\28@081847 by Roman Black

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John De Villiers wrote:
>
> > Does anyone have any sound hypothesis (or better yet - real world
> > knowledge) about what happens when the fuel line to the injectors is
> > depressurized, as far as damage to the car?  (obviously it won't run well,
> > if it runs at all)
> As far as damage goes i dont think there is much that can go wrong. The fuel
> pump pumps like mad to keep the pressure in the injector bar up at whatever
> level it needs. It has a preasure bleedoff so that when the bar is at the
> desired pressure the fuel is just pumped back into the tank.
>
> Letting it run dry is a big fubar as you now have to bleed all the injectors
> to get the air out. NOT A FUN EXCERSIE.


I don't think it's quite that bad John, in the
old hot rod days of FI, the FI system was just
a pump with a return valve, and the throttle
operated a simple flow valve that controlled the
flow/pressure to the jets. It works alright.
I don't think air will get in there, just if
there is less pressure to the jets there will
be less (or no) fuel actually injected.
-Roman

PS. My motorcycle is a new fuel injected type,
the '98 model was recalled with a FI system
problem related to a hose leak on the fuel pump
which caused pressure to fall. This simply caused
intermittant running when the pressure leak
was occuring.

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2001\01\28@100649 by Ray Russell

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In a message dated 1/28/01 8:20:43 AM Eastern Standard Time,
spam_OUTfastvidTakeThisOuTspamEZY.NET.AU writes:


{Quote hidden}

Guys,
I have been following this thread for a while. I am a mechanic by trade so
here are some facts. If you depressurize the fuel system the car will not
start. If you vent the fuel to the atmosphere you run the risk of fire.
Especially if the jerk gets pissed and flicks his cigarette back at your car
as he is running away. If you install a valve and run the fuel back into the
tank this would work but is a lot of work. Simply cutting out the power to
the fuel solenoid is much simpler. If you interrupt power to the fuel and
spark systems the car is not going anywhere unless it is towed. This is
probably the most cars get snatched these days. If your car is on the top ten
list you can bet your A$$ that if someone is going to steal it then it will
be on the back of a wrecker.
The only defense for this is a lot of noise that cannot be stopped by cutting
the battery wire.
The best way to defend your car is to cost the jerk to spend time to get your
car. the more time he feels he is going to have to spend the less likely you
are to get bitten.
As for all the other wonderful gismos you guys have come up with most if not
all are going to land your A$$'$ in jail next to the same anal pores that are
out there stealing your car.
Install surveillance equipment in your car! Record them having all their fun
and then laugh when they try to tell the judge their "Innocent"!
Ray Russell
General Contractor
Norfolk & Western Railroad

Pocahontas Division
Circa 1958
Visit The Pocahontas Website at:
<A HREF="http://milliron.home.sprynet.com/Pocahontas/Pocahontas1.htm">Click here: Pocahontas Home</A>
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http://milliron.home.sprynet.com/Pocahontas/Pocahontas1.htm

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2001\01\28@103910 by Roman Black

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Ray Russell wrote:

{Quote hidden}

You've said some good sensible points Ray, I just want to
add that a person on this list has been working on a
new type of fuel injection controller for vehicles
that uses a PIC to perform some real time adjustemnts
to the fuel pressure (and hence injected volume).

I was under the impression that the original suggestion
related to this, not to the "car theft" topic. Obviously
if you just wanted to disable the FI you could cut power
to the electric fuel pump. Some car alarms already do
this.
-Roman

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2001\01\28@133041 by dre Domingos F. Souza

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>As far as damage goes i dont think there is much that can go wrong. The fuel
>pump pumps like mad to keep the pressure in the injector bar up at whatever
>level it needs. It has a preasure bleedoff so that when the bar is at the
>desired pressure the fuel is just pumped back into the tank.
>Letting it run dry is a big fubar as you now have to bleed all the injectors
>to get the air out. NOT A FUN EXCERSIE.

       I know it happens in DIESEL motors, not in gas/alchool ones.


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       All the best!!!
       Alexandre Souza
       .....xandinhoKILLspamspam@spam@interlink.com.br
       Linux User #85093

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