Fuel Pump Relay question

[Chris Hall]

Jim Jordan wrote:

"the backfire is raw fuel that got to the cat and/or muffler.  When we
were kids, we used to blow the guts out of mufflers by turning off the
ignition briefly letting the raw fuel pass through the engine, then,
while still rolling in gear, turn on the ignition with a big bang."

That doesn't make any sense to me.  

I always thought that if a car backfired, that it meant un-ignited
fuel hanging around in a cylinder was being detonated at the wrong
time by a mis-fired spark plug when the exhaust port was open in that
cylinder.  You seem to be saying it only happens when too much fuel
goes in to the engine, passes wall in to the exhaust system, and the
heat within the exhaust ignites the fuel and goes out the muffler.

How the hell would gas -in the cat or muffler- as you say, POSSIBLY be
ignited when the ignition is switched back on?  It'd HAVE to be near a
spark plug to do that... and I sure as hell don't have a spark plug in
my exhaust system that would ignite fuel in the cat / muffer when I
switch the ignition on.

Would it be a safe assumption then that my ECU is cutting power to the
coil, the fuel pump keeps pumping gas for a second or two in to the
engine (I've witnessed this while observing the fuel pump relay with
it's cover off after the engine dies), and when the ECU cuts back IN
(for what ever reason) sometimes, that it's igniting gas in cylinders
who's exhaust ports are open?  As I said, I sure as hell don't have
any spark plugs in my cat or muffler that would ignite un-spent gas
when the ECU switches the ignition back on the same way you did as a
kid to cause a backfire... and I'm sure you cars didn't either.

My friend used to do the same thing in his old Chevy truck.  Turn off
the key, keep it in gear so the wheels spin the trans which spins the
engine and the mechanical fuel pump, feeding gas to all cylinders,
then switch the key back on, and BAM.




On 6/6/05, Jim Jordan <superba at comcast.net> wrote:
> Hi Chris,
> 
> Well, as I said before, the backfire is raw fuel that got to the cat and/or
> muffler.  When we were kids, we used to blow the guts out of mufflers by
> turning off the ignition briefly letting the raw fuel pass through the
> engine, then, while still rolling in gear, turn on the ignition with a big
> bang.
> 
> Something is dumping huge(relatively) amounts of fuel in the engine at
> times.  The waiting period, ~10 minutes as I understand it, is consistent
> with letting a flooded engine clear out.  The next time it does it, remove
> the coil wire and clear it by 4 or 5 15 sec on and 15 sec off start tries
> with the starter.
> 
> HTH.
> 
> Cheers!
> 
> Jim Jordan
> 
> >
> >
> >  By the way... there can only be -so- many things that will
> >  cause the car to BACKFIRE like it sometimes does when it's
> >  stalling, right?
> >  Anyone know what those things are?  I imagine that'd help us
> >  narrow it down...
> >
> 
> 


-- 
Chris Hall
badcomrade at gmail.com
"making girls cry since 1974"