[s-cars] By-passing the CPS

Michael Wakefield S4Quattro at comcast.net
Fri May 11 22:53:06 EDT 2007

Here's some information that may influence your logic process, since  
the sensors serve different purposes.

The camshaft position sensor signal is used to recognize the ignition  
point for cylinder number one for starting the engine. The signal is  
also used for cylinder selective knock control and to determine  
injection timing and sequence. The engine can't be started if there  
is no camshaft position sensor signal, but if the signal fails during  
engine operation, the ignition timing will be retarded by 11 degrees.  
In addition, the boost will be reduced and knock control will be  
disabled stopped.

The crankshaft position sensor (the upper sensor of the two on the  
left side of the block by the flywheel) signal is used to provide the  
cylinder number one top dead center signal. This signal along with  
the signal from the camshaft position sensor is used for engine  
starting. If this sensor fails while the engine is running, it will  
keep running. if the engine is stopped, it can't be restarted.

Mike Wakefield
Highland Ranch CO

On May 11, 2007, at 4:03 PM, Vincent Frégeac wrote:

> I’ve read somewhere that the role of the CPS is to tell the ECU the  
> starter
> is actually cranking the engine so it’s OK to activate the fuel pump
> (something you don’t really need a buried in 8h of work sensor to  
> realize).
> Then, the engine speed sensor takes the relay and tells the ECU to  
> keep the
> fuel pump running. This brought two questions to my mind:
> -          Would a check light on the fuel pump wires be a good way  
> to tell
> if the CPS is the problem, at least for the warm-start problem I’m  
> having?
> If the fuel pump does not receive the expected ~12V when the  
> starter crank
> the hot, not starting engine, but does when the engine is cold,  
> it’s a CPS
> problem. If it’s receiving 12V when the engine is hot, look elsewhere.
> -          Would a wire from the starter solenoid wire to the fuel  
> pump,
> with a diode on the existing fuel pump positive wire to avoid  
> frying the
> ECU, be a good way to get rid of the CPS problem until I have time  
> to go
> through the timing belt and CPS, which is not exactly the case  
> right now,
> except if I start considering sleeping time as optional?
> I can’t see any logical reason this wouldn’t work but before I fry  
> the ECU
> with my somewhat tired logic, I though pinging the list wisdom  
> would be
> safer.
> -          Optional question: Why in the hell did they use two  
> engine speed
> sensors, which means two reason to fail on us, when one would do  
> the job? I
> mean, when the ECU would realize that the crankshaft is turning but  
> not the
> camshaft because of a broken timing belt, it’s way too late to save  
> the
> valves and pistons anyway, and the engine would have probably  
> stopped by
> himself by loss of any compression, or intake or exhaust or whatever.
> TIA for your help on bringing reality check to my poor beaten up  
> logic.
> Vincent
> ’96 S-Bitch keeping me busy and frustrated
> ’81 Fiat Spider 2000 I would’nt qualify in fear my post would be  
> rated 18+
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