Waveform on camshaft position sensor?

98 Escort throws P0340 (camshaft position sensor) under certain specific conditions, fairly easy to reproduce. The CMP checkout procedure I've read on Autozone is very crude; it simply uses a DVM to
verify that the average voltage increases as rpms increase. I want to hook up an oscilloscope and look at the sensor output properly. What should I expect to see? Approximately symmetrical square wave?
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snipped-for-privacy@larwe.com wrote:

Check this link out:
http://www.wellsmfgcorp.com/counterpoints/Counterpoint3_1.pdf
It should tell you what you want to know.
Bob
-
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Thanks, interesting info. I'll brave the cold and go out after lunch with my scope.
Found out that *most* of the rattling/throbbing noises on this vehicle are due to broken fastenings between the various splash guards under the front end; just spent the morning drilling and holding everything together tightly with poprivets. But there is still definitely something iffy about idle and I don't know if this P0340 is implicated. It only seems to show up when someone ignores my BIG RED STICKER INSIDE THE GAS DOOR and puts premium gasoline in the beast.
The header panel is also held by only one bolt at this time (two tabs are broken, one bolt head is broken off). Not good. Hope I can get it off easily. Guess that's next weekend's project.
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Rule of thumb... 3 wire sensor will usually ba a hall effect switch and should give a square wave. 2 wire sensor is a reluctance type sensor and should give what looks pretty close to a sine wave.
The square wave volt peak will be around 5.0 VDC while the voltage peak on the relucance sensor will usually increase with rpm.
Be sure that your scope has a high input impedance.

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and
and
Just as a matter of interest - since Bob's PDF pointer didn't get into specifics - the Escort's is a 2-wire type. If it's NOT functioning correctly, what will I see - low amplitude? Skipped cycles?

1M, ought to be high enough.
Thanks for the reply.
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IIRC, you should see one skipped cycle... (working from an old mans memory here and my manuals aren't close to hand). I would think that there should be a "signature" that the PCM can count from to determine position so expect to see one drawn out wave amongst the rest. Most common problems are an open or short.... a short would deliver lower than expected amplitude (depending on the nature of the short) right down to a flat line. An open would also give a flat line (but I'm sure you know this since you have a scope.... threw it in for the less knowledgeable). I'd also look to see if the signal was dirty... RFI can play havoc with these sensors (hence the twisted pair harness).
Fords test procedure doesn't include using a scope on the sensor. Be aware that it is possible (if the connector hardshell has been apart or replaced) to hook these sensors up backwards. AFAIK, there is no way to be to check for this electronically... if you need, I'll try and remember to bring my laptop home (it has the manuals on the HDD) when I'm uptown later and we can check colour/pin assignments.
HTH
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