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I cannot fully answer the question (sorry). I thought I had a problem with one of the crank sensors myself on a MOCA member's swap. A master Mazda tech was super friendly and was walking me through the test over the phone. He said that I should get a battery tester (uses 3-4 small lights to show voltage, looks like a circuit tester, but is different) Then when testing the sensors I should see a wave pattern in the lights. (lights light up going from bottom to top and back to bottom and back to top, like 1-2-3-3-2-1 and so on and so on) This is because the sensor only tells when at TDC and thus you see a wave of when the voltage is being sent. A usual tester will not be good for picking this up b/c they are so sensitive that it is hard to see a pattern. The real tester for this is a special mechanics tool that will actually read wave patterns, but they are super expensive.
I also did the resistance test and got a positive result on the "real" CAS. I don't know if you can do a resistance test on the disty CAS. However, all the sensors tested ok and it turned out to be clogged injectors in my case.

PATDIESEL wrote:I cannot fully answer the question (sorry). I thought I had a problem with one of the crank sensors myself on a MOCA member's swap. A master Mazda tech was super friendly and was walking me through the test over the phone. He said that I should get a battery tester (uses 3-4 small lights to show voltage, looks like a circuit tester, but is different) Then when testing the sensors I should see a wave pattern in the lights. (lights light up going from bottom to top and back to bottom and back to top, like 1-2-3-3-2-1 and so on and so on) This is because the sensor only tells when at TDC and thus you see a wave of when the voltage is being sent. A usual tester will not be good for picking this up b/c they are so sensitive that it is hard to see a pattern. The real tester for this is a special mechanics tool that will actually read wave patterns, but they are super expensive.
I also did the resistance test and got a positive result on the "real" CAS. I don't know if you can do a resistance test on the disty CAS. However, all the sensors tested ok and it turned out to be clogged injectors in my case.

Thanks for that Pat. Ya it's a typical sign wave (more or less) that the SST would see when turning it by hand. I went to the local Mazda and they don't even do that anymore. A Mazda directive now.. They don't even repair disty's in the shop any longer if the the igniter or coil goes. The overall costs that Mazda was charging to repair both of those items (parts and labour) was just shy of the cost of a new disty anyway so they made a directive to stop the repair and recommend replace only as a rule of thumb. I'm hoping there's a few auto electric guru's that might know there way around this. Another option may be to go and query the local Ford shop wrt to a similar problem with a 93 PGT since I'm guessing the 92 MX and the 93 PGT probably had the same disty config.... *fingers crossed*. I might even post this query on the PT BB too. But who knows, maybe Yoda or some of the other senior members may have a trick or 2 up their sleeve. Thanks Pat!!

jschrauwen - just curious - if you had faulty CAS wouldnt you also have problems running with any other ECU. After all the ECU uses those signals to determine when to start firing - if it was faulty or the connection was bad then it would show up as a major problem wouldnt it?

ariesdude wrote:jschrauwen - just curious - if you had faulty CAS wouldnt you also have problems running with any other ECU. After all the ECU uses those signals to determine when to start firing - if it was faulty or the connection was bad then it would show up as a major problem wouldnt it?

Ahhhhhh, ariesdude that was EXACTLY my thinking also when I said nearly the same thing to Ryanpzz at Probetalk. This is what is believed to be the crux of why I couldn't get my Megasquirt to work. The Megasquirt was not seeing the engine turning over which will inturn not apply any spark or fuel until it does see that. I have to send my Megasquirt back to him in Florida so that he'll be able to use another source (if possible) within the KL31 ECU to tap into to get that signal. Apparently Mazda was redundant in the earlier years when it came to sensors as we know in the case of the coolant thermosensors between the 92 to 94 (I believe) where the 3rd coolant thermosensor was later dropped. Which is ironic because around that time they went from 2 O2 sensors to 4 I believe.
Anyway, Magatune just doesn't seem to see the engine turning over when I'm cranking it so an alternative would be to have the Megasquirt tap into another viable source within the KL31 ECU that is being used with it. Two possible sources would be the Crank Angle Sensors. As I mentioned< I've already verified the serviceability of CAS2 and now I'm trying to find a method to verify CAS1 (within the disty)without having to remove the disty completely since I don't have a Mazda SST tool to check it with anyway (and strangely, neither does my local Mazda). I would have imagined that CAS1 would be the primary signal to the ECU in the first place.

John

The Cam angle sensor in the disty would be the primary sensor (i assume) because 1.6L DOHC doesnt have an extra crank angle sensor. I think mazda put the extra CAS for the V6 because there are two banks of cylinders with 2 sets of cams - but the disty sits on the front bank only. Besides the timing is adjusted by rotating the disty - not the crank angle sensor.

Another possible way to check if they are ok is to either pull codes from your ecu or from a spare k8 ecu......

Unfortunatley if your not a tech/mechanic you probably won't have a lab scope. A lab scope is the bottom line for sensor outputs, resistance readings are good for condeming parts but viewing the actual output that the ecm uses is a far better test. Hall effects, schmidt triggers, windows or shutters produce a square wave and magnetic pickups produce a sine wave, oh yeah led or optics also produce a square wave. there is a lot of room for error when using other methods.
PS I've worked at dealerships, been wrenching for 18? years, own a shop and can say techs almost never use the "engineers" trouble tree. sometimes they are just silly.

Well if you do happen to find an effective way of verifying the cam angle sensor in the disty, please inform us, as I am having this issue right now too.

tehbrookzorz wrote:Well if you do happen to find an effective way of verifying the cam angle sensor in the disty, please inform us, as I am having this issue right now too.

Glad you said that and I hope Philthy is listening. Could really use a professionals insight on this one. It may be the showstopper that keeps me from being Megasquirted.

Ok guys here goes, dug up some schematics and waveforms. ECM's and modules use voltage signals to convey information as well as controling solenoids, ignitors, injectors, etc. When i test crank/cam sensors I use a labscope ( that means your looking at the voltage on a screen with a graph theat reads voltage top to bottom, and time left to right) this is as opposed to a multimeter that shows you a numerical value representing a voltage. Multimeters are to slow for most electronic testing. Mind you a good multimeter is still a valueable tool. You can get some information using a multimeter or test light but not enough to know whether a component is truly good.

this is a diaqram of a magnetic pick-up which produces a sine-wave
This not the same as what is in our disributors. this is whats mounted by the crank pulley. Ive made notes in the pictures.


This a typical sine-wave when viewed on a lab-scope


Now onto the distributor, first a Mazda diagram then a schematic note the circled symbols.



when transistors are used they produce a square wave, If the windows are evenly spaced (windows or shutters are the blades or slots that spin through the sensor indicating cam or crank position) then the squares are evenly spaced.
Here iv'e circled the fault in this square wave. I have also created other examples of a faulty waveform in red.


On our cars the "SGC" signal (in the distributor) will indicate a "square" when cylinders 1 and 4 are at tdc
the "SGT" signal (also in the distributor) represents crankshaft angle in 60 degree increments, one "square" for each cylinderIn the auto repair business we purchase lab scopes from Snap-On, Mac Tools, Matco, Ferret, Fluke, OTC and a whole bunch more. I have never done the research for a cheaper do it yourself model. Also poor resolution and refresh rates (i.e. a cheap scope) can lead to frustration. I personally have not been disappointed with fluke products.
Also, it is just as important to check powers and grounds with a lab scope. Power and grounds should basically be clean flat lines. Note that during cranking the power voltage will fluctuate.
also note grounds are often overlooked and very important. I would be concerned over any ground that exceeds .05 volts.
The schematics i used are mazda schematics and the waveforms I found posted on IATN.org
I hope this answers some questions, but if u can't get your hands on a scope I guess this post just sits in the geewhiz file.
I'll try to answer any questions.
PS any fuelinjection system mazda, megasquirt or otherwise is going to be using similar sensors.

FAQ or at least stickied material please.

Er John thank Philthy not me mate.

kiwi_MX3 wrote:Er John thank Philthy not me mate.

Oh sh*t...sorry!!!! Philthy appologies and also many thanks for the CAS info. Now hopefully find a reputable mechanic that's willing to do this. In this world of replace rather than fix, it's probably getting harder allof the time to find some one with hands on experiance in doing tasks like this.

jschrauwen wrote:

kiwi_MX3 wrote:Er John thank Philthy not me mate.

Oh sh*t...sorry!!!! Philthy appologies and also many thanks for the CAS info. Now hopefully find a reputable mechanic that's willing to do this. In this world of replace rather than fix, it's probably getting harder allof the time to find some one with hands on experiance in doing tasks like this.

No worries john, you canna borrow ma spec's any time, just hands
off me zimmer frame...

Looking at those diagrams, I notice that before the cam angle sensor is the 'main relay.' Is this aka the Circuit Opening Relay under the dash? Could one safely assume that if there were issues with the main relay (it was operable but only at intervals), that it could cause issues such as Code 2 and Code 4, along with intermittent stalling (sudden tach drop followed by engine dying). If this is so, I need to know! Also, if the 'main relay' is not the circuit opening relay behind the ECM, then where is it?