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- Leonard Caillouet
January 28, 2006, 3:45 am
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Re: Z3 1997 M44 ODB code P1423 Secondary Air System
P1423's are a classic Z3 problem.
The key is to replace both the check valve *and* the air pump, not just
the air pump. The check valve is root of the problem: it's letting
water vapor from the exhaust manifold flow into the pump, which is
corroding the pump.
I _was_ going to replace just the air pump, but my BMW technician buddy
strongly suggested I replace the check valve as well, otherwise the
pump would fail again quite soon. 30,000 miles later, and the air
pump is still doing fine.
[ BTW, the part numbers/prices are:
[ o check valve, $94, BMW p/n: 11 72 1 744 255
[ o air pump, $268, BMW p/n: 11 72 1 432 907
[ Reference: http://www.realoem/com
Where's the water vapor coming from?
It's actually a natural byproduct of combustion. I was very skeptical
at first, but have since learned that engines actually produce a huge
amount of water during combustion... approximately one gallon of H20
for each gallon of fuel burned (!)
Seems to fail the "straight face" test - how can you get a gallon
of water out of a gallon of gasoline? By adding 15 "gallons" of air.
In other words, it turns out that the A/F (air/fuel) ratio is about 15:1,
so along with that 1 unit of fuel is 15 units of oxygen. If you
look up the combustion equation for petroleum as well as the
atomic weights for the reactants and products, it does indeed
turn out that for each gallon of gas burned, a gallon of water
vapor is produced. Odd, but true.
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