Viewing Cam and Crank '97 Mercury Mystic 2.0

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Viewing Cam and Crank '97 Mercury Mystic 2.0

Postby hexibot43 » Tue May 29, 2012 4:45 pm

CamAndCrank.JPG
Schematic Diagram Cam and Crank


Hello,
I am curious if there is a good way to look at Cam and Crank Signals on a vehicle like this. I have two AC pulse generators that don't seem to share a common ground. Is there a way to use Math channels to display these two signals on my Picoscope 4423? Or do I really need a differential scope probe for each signal? Ouch! Could I put Crank + channel A, Crank - Channel B...and then with math Add them together to get a good reading using the block as my common ground? I have four channels so could do both signals if this will work. I keep running across this with Crank Sensors. Usually the Cam is Hall effect and no issue.

I was just reading the post on Chrysler 3.3l broken flex plates. I believe this vehicle does the same thing. We were about to tear the transmission out when I read this post. Now I've just got to get it up on my scope to take a reading.

Thanks,

Marcello
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Re: Viewing Cam and Crank '97 Mercury Mystic 2.0

Postby Alan » Tue May 29, 2012 7:03 pm

Hi,

Its not a vehicle I am familiar with but my guess is that one side of each sensor is grounded within the ECU.

Connect CHA black lead to a good ground (chassis / battery negative) and probe both sides of the crank sensor in turn. If one side has a signal and the other does not then repeat with channel B for the crank.

If both sides have a signal then it depends on what you are trying to do - if its check the timing relationship then the above will still be OK, you may not see the full signal amplitude but enough to compare timing.

If both sides have a signal you can also as you suggest measure deferentially using 4 channels. Connect all the black leads to ground then use channel A for one side of the crank and B for the other. Repeat with C and D for the cam. You can now add 2 maths channels for A-B and C-D.

You will now have 6 traces on the screen, you can either move ABC&D out of the way by dragging the axis up or down or right click and under channels you can hide them.
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Re: Viewing Cam and Crank '97 Mercury Mystic 2.0

Postby Autonerdz » Tue May 29, 2012 8:05 pm

Gee, Alan. We were just discussing this the other day when I explained to you the technique to approach these sensors without need of a differential scope. Good explanation. :wink:

Here is some more on that....Math channels are so cool. 8)

Marcello,

Your EDIS system has a floating ground CKP and a non floating CMP.

To review...The EDIS CKP is a VRS two wire sensor with no ground reference. In the past, there were two ways of looking that these using a scope with common channel grounds.

1. You can place the signal and ground for a single channel across the sensor. This prevents you from grounding the scope or using any other channels. This is because the scope common ground would ground out the CKP. The advantage of this method is that the full peak to peak signal amplitude and the correct ground reference through the signal center will be shown on the scope. The disadvantage is that you could not use this hook up to do a CKP/CMP relationship check.

2. You can ground the scope and place a channel signal wire onto one of the CKP wires, choosing the correct one so that the waveform is right side up. The disadvantage is that now the CKP true amplitude will be reduced by about 50% on the screen and the signal will float a bit off ground. The advantage is that now you can deploy other channels. Now you can do a CKP/CMP relationship check.

With channels math, we now have a third option to have the best of both worlds. Examples are below.

The first image shows the CKP with the scope grounded to bat neg, channel A on the right side up leg of the CKP and channel B probing the other leg. Note the rulers at channel ground and the peak to peak voltages.

edisckp2ch.gif
EDIS CKP A pos B neg


The second image shows the CKP as it really is with channel A across the sensor. Note how ground is now at the center of the waveform and the peak to peak amplitude is doubled.

edisckp1ch.gif
EDIS CKP viewed differentially using one channel.


The third image shows the first one again with an A-B math channel added. Note how the math channel looks a lot like the single channel capture.

edisckp2chmath.gif
EDIS CKP using two channels plus math


The fourth image is the math channel with the single channel capture as a reference waveform overlayed on top of it.

edisckp2chmathref.gif
EDIS CKP two channels plus math and the differential capture overlayed on the math channel to show they are identical.


So, we can now use channels math to see the CKP in its full glory as it really is while keeping the scope referenced to bat neg and still have two more channels to deploy as needed. :shock:

Since your CMP is non floating you can simply probe the one wire that has the signal and view it as usual.

The above posted in the Autonerdz Community Forums Picogroup area July 1, 2010.

http://www.autonerdz.com/cgi/yabb2/YaBB ... 1278004259
Tom Roberts
(The Picotologist)
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Re: Viewing Cam and Crank '97 Mercury Mystic 2.0

Postby hexibot43 » Tue May 29, 2012 11:55 pm

Thank you both for such fast and helpful insight. I was really hoping to get this answer....and I'm glad to see that I was mistaken about the cam sensor. That will give me that third waveform I always seem to need in reserve. This falls in line with what I've seen in other cars....Crank Floating...Cam not. Better yet, I'm going to be able to do it without getting anything more! :lol: This answers a question I've come across quite often with Crank Signal. Feeling good about my choice of scopes to purchase.

Thanks,

Marcello
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