4KQ fool pump and brake MC

[mike]

As far as I know the pump runs for a short time (10s?)
when the ignition switch goes from off to on but after
this it needs the tach signal to run.

The idea is the short run at the beginning gives
enough fuel to start the engine but if you lose the
tach signal (like you would if you had an accident
which broke a fuel line) then the pump doesn’t try and
empty the fuel tank via the broken pipe

--- Huw Powell <audi at humanspeakers.com> wrote:

> 
> > A signal from the tach activates the fuel pump
> relay?  I thought it 
> > used to turn on as soon as the key was turned on.
> 
> The tach signal is required to keep it on.  The
> brief activation upon
> "key on" was determined to be a fluke due to that. 
> Otherwise it doesn't
> run til the engine is turning over.  And stops when
> the tach or power stops.
> 
> > Brake pedal gets a firm spot, but real close to
> the floor.  I'll try 
> > another bloodletting, er, um, bleeding.
> 
> Oh, that may also be a sign of one of the two
> circuits failing (internal
> leak).  It then takes longer for the other circuit
> to pump up.
> 
> >> Fuel pump on milady's 4kq camping car won't run
> unless I jumper the
> >>  two big spaces in the relay tray. Then it runs
> fine. Put the relay
> >>  back in and it won't run. Is the pump drawing so
> much juice the 
> >> relay won't pass it on or is the relay just
> toast? Car has been 
> >> sitting a month or more.
> > 
> > 
> > The relay is probably bad, it would be nice to
> test with a known good
> >  spare, though. If somehow the tach signal is not
> getting to it, it 
> > would not "turn on".
> > 
> > 
> >> Brakes work OK, but used to be really effective
> and didn't take a 
> >> lot of pedal to operate. Today the pedal almost
> hits the floor. 
> >> Reservoir is at "Max" like it has been since I
> flushed the system 
> >> last summer. Did the MC maybe burp and lose some
> of its seal? Do I
> >>  need new?
> > 
> > 
> > Is the pedal firm eventually, or does it sink
> under pressure? A 
> > sinking pedal with no leaks tends to indicate a
> bad master. A soft 
> > pedal that reaches a firm point tends to indicate
> air in the system, 
> > although how it could get there without lines
> being opened recently 
> > would be a mystery.
> > 
> 
> -- 
> Huw Powell
> 
> http://www.humanspeakers.com/audi
> 
> http://www.humanthoughts.org/
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