[V8] Crank & RPM sensor diags

[RockinV8Q@aol.com]

IME.....
 
 The V8 will nearly always code an RPM sensor if its causing a no  start.
 
 The V8 will sometimes code the crank angle sensor if its causing a no  start.
 
 Reason..... The Motronic is looking for the crank angle sensor pulse  
anytime the key is on, even if the engine isn't being cranked and the  fault 
recognition isn't programmed to trigger a code if it counts X teeth  without a crank 
angle pulse. I believe the reason for it sometimes coding the  crank angle 
sensor in a no start is that the fault recognition is programmed to  see a very 
weak signal as a fault...just not smart enough to see no signal at  all as a 
fault.
 
 OTOH....
 
 If the V8 is running and loses the crank angle pulse it will always  trigger 
the code even though loss of the signal has no effect on engine  performance. 
 
 The V8 will rarely code an RPM sensor that fails and causes the  engine to 
shut down.
 
 Reason.... The Motronic usually doesn't recognize that loss of the  RPM 
sensor while switched power to the Motronic is still present as a fault. 
 
 The no start tends to be true regardless of the model  year while the engine 
running fault recognition seems to get better with  later years, 90's seem to 
have the worst, 91's slightly better, 92-94 much  better than either of the 
earlier two years.
 
KT