NO-Start Diagnostics

[bmrfamly <bmrfamly@xxxxxxxxxxxxxxx>]

Gentlemen
   If a "normal" motor suddenly refuses to start, the problem is 
usually related to spark, or fuel.  Check for spark first, as it's 
easier and safer.
   To check for spark, install a "spare" plug in a conveniently 
located plug wire, (never hold a plug, or plug wire near ground while 
cranking as it will kill the electronics....maybe you too) ground the 
plug base, STAND WELL CLEAR, and "crank the motor over" while 
observing for spark.
   If there is no spark at a plug wire, repeat this process with the 
plug wire installed into the coil, this eliminates potential problems 
with the distributor cap & rotor and "high tension" lead from the 
coil.
   Still no spark, by-pass the "MAIN" relay (controls ignition & 
injection on many BMWs) with a home-made harness using 3 male spade 
clips and a few inches of adequate gauge wire.  Remove the relay and 
carefully locate the terminals within the "relay socket" (if the 
socket isn't labeled, the relay should be) Bridge terminals #30 (HOT 
=12V) with both #87 (APPLIANCES = Ignition/Injection, and Fuel pump 
relay).   *Note: sometimes #30 is always hot, sometimes it's switched 
by the ignition, so the key would have to be in the "RUN" position.
   Still no spark, check the crankshaft speed/position sensor/s, for 
cleanliness, position of attachment, and electrical resistance, and 
output.

   Well, let's say you found spark somewhere along the way and there 
still is no start, so we suspect fuel.  You either have too much, or 
little.
   Too much may smell, and leave plugs wet.  This may happen a few 
minutes after shutdown due to a leaking injector.
   Too little/none is more common.  The common culprit is the fuel 
pump relay which can be by-passed with a home-made harness using 2 
male spade clips and a few inches of adequate gauge wire.  Bridge 
terminals #30 (HOT = 12V) and #87 (APPLIANCE = Fuel Pump).
   You can feel the fuel "pulse" thru the lines, and hear the pump it 
it's quiet enough.  No feel/hear.......have a trained professional 
remove the high pressure fuel feed line and test for fuel pressure.
   Note* always check for spark before checking for fuel.  Many 
stories abound about people that found fuel, then spark.
   Caution* Never drive a vehicle with the "test harnesses" in place, 
as there would be no way to "shut-down" automatically in case of 
emergency.
   e-mail me off this list for pictures of the test harnesses.

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