[s-cars] CMPS signal shape (was Location of CPS?)

[Paul Gailus]

Konstantine,

If you had AC coupling selected on your 'scope instead of DC coupling, that could explain the upward slope you're seeing on the bottom of the negative pulse from the Hall sensor. It would also explain the downward slope at the end of the pulse.
Was the 200tq engine running (instead of cranking) when you took the measurement?  I suspect the engine was running based on your comment about a "different scale".  A shorter pulse duration with the engine running would explain why the pulse appeared to be flatter on the bottom (less time for it to ramp up).

Anyway, back to the real problem at hand. I agree that the relative timing of the sensor outputs looks good, so you should probably focus on the fuel system. Before you leave the ignition though, make sure you've got a consistent 12 volts to the coils. I had an intermittent short in a coil of my urS4 that would trip the thermal breaker. The breaker would sometimes reset long enough to let the engine catch and run for a very short time.

Paul

-----Original Message-----
>From: Konstantine Bogach <kbogach at comcast.net>
>Sent: Dec 31, 2009 12:03 PM
>To: s-car-list at audifans.com, forgied at shaw.ca
>Subject: [s-cars] CMPS signal shape (was Location of CPS?)
>
>Ref:  UrS4 does not start.
>I observed relative location (timing) of signals from CMPS (cam, I also 
>use Hall sensor term) and CKPS (crank) on my (running) 200tq and UrS4.  
>200tq has perfect timing - TDC pulse is right on the middle of the 
>negative pulse from Hall sensor, which is a rectangular pulse.  Bottom 
>of the negative pulse is not horizontal but the pulse still have 
>vertical front and tail (a better term should exist, I think).  The 
>ratio of pulse widths is 8-10 to 1 (CMPS to CKPS).  On S4 TDC this ratio 
>wa s 2-3:1.  This is just visually, I did not measure the width.
>  But I can not call signal from S4's Hall sensor a rectangular pulse.  
>Here how it looked like:
>
>            |
>              \
>                   \
>__                 \_________
>   |      /
>   |    /
>   |  /
>   |/
>   A      B     C
>
>      ^ - location of the TDC pulse (betwee A and B) on S4.
>
>In 200tq the bottom of the negative pulse looked like this:
>
>            |
>              \
>                   \
>__                 \_________
>   |
>   |
>   |    _ --
>   |_--
>   A      B     C
>        ^  - location of the TDC pulse
>
>|AB| would be different on these two pics (different scale).
>I was expecting to see TDC signal not aligned with CMPS signal and this 
>would explain no start condition.  But looks like relative position of 
>the pulses is good, but I don't know if the signal produced by CMPS on 
>S4 is good.  Anyone has comments?
>Also, anyone knows a source for fittings which can work with regular 
>fuel pressure gauge from a FLAP.  The set I have has no fitting for S4 
>(but I can use it on 200tq).   Maybe I don't have fuel pressure.  I can 
>hear that fuel pump works though.
>
>Konstantine
>
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