<E28> Poor Fuel Economy UPDATE ...

[khensley@xxxxxxxxxxxxxxxx]

I have been to the Digest twice for information on my poor fuel 
economy.

Now to report my progress so far.

Initial indications:
My '85 535i's fuel economy went "sour" suddenly.  Along with it was 
poor starting, and poor idling - plus a lot of black smoke! 

Check and replace:
I checked everything I could easily check - temperature sensors, etc. 
 The easy stuff.  It was time for a tune up - and time for the idle 
control valve to fail - so the car got plugs, wires, distributor cap, 
rotor button, and idle control valve all replaced.  The car started 
somewhat better - and the idle was much improved.  The fuel economy 
was still poor.

Narrowing it down:
I was left with the fuel pressure regulator, cold start valve, and 
ECU as possibilities.  Easiest thing to do was the fuel pressure 
regulator.  Replaced it.  Fuel economy got WORSE!   WHY??

Down to 2 items - cold start valve and the ECU.  What a pain!

Cold start valve:
WHO decided on the location of this thing?  Poor isn't the word for 
it!  I wanted to test the thing.  How?  This was going to be a PAIN!  
Time for an idea.  I disconnected the hose from the fuel rail.  
Taking a new piece of short hose, I connected it to the fuel rail - 
and plugged off the other end of the hose with fittings that could 
take the high pressure.  The open hose to the cold start valve I 
capped - so it could not suck air into the manifold.  The car 
started - and I had a leak in the fitting.  Fixed it - now to drive 
the car and observe the fuel economy.

OBSERVATIONS:
My fuel economy is better!  Much improved!  The culprit was the cold 
start valve (so far).  If you will notice, I have not replaced the 
valve.  I have taken it out of service!  WHY does it exist?  My 
coldest morning so far is 28-deg. F. (-2 C).  With opening the 
throttle slightly, the car cranks up fine!   The car STARTS BETTER!   

If your car is hard to start, consider the cold start injector.  With 
my cold start injector being "open", it was bleeding the pressure off 
the fuel system!  I had to crank the car longer - to get the pressure 
and gasoline back up!  This had been going on for a while!  The cold 
start injector should have been replaced (OR disabled!) long ago!

Thank you all for your help.  Now to be monitoring the car!

...Kim Hensley
Danville, VA
BMW CCA #16216

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