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Hi guys,

I see that ignition problems seem to be one of the commonest things that go wrong with MX-6s. Having recently had this issue myself and successfully solved it, I thought I should share what was wrong and how I went about it. I should confess, it was greatly due to having this forum site to refer to that I was able to do it so easily. Also, the problem that I had may not be the same as what others have, but I'll go through the general fault finding order that I went through.

A few weeks ago, after just a few months of owning it, I went to start my '93 MX-6 and it mysteriously had a flat battery. It had gone flat on its own far too quickly and there was no reason for it. So I charged the battery and suspected a current drain somewhere. This problem happened again just once but then it stopped. I was still using the car during this time.

The day or two after this episode I tried to start the car but would do is turn over. It had worked faultlessly until then, but it would not start. The battery soon ran flat and with a jump start, it suddenly fired again.

Somewhat randomly, the car would either start or not start. With a jump start it seemed to start more often. I quickly concluded there was no spark and started reading up on mx6.com and found how common ignition problems are. The problem I had is best summed up by the fact the car wouldn't start, but once it was running it wouldn't stop running. Unfortunately this car doesn't have an engine check light, so I was unable to read OBDI codes from it.

So to start I opened the distributor and all seemed well, no unnecessary wear or damage. Unfortunately, an earthing wire seemed to just break off the back, but repairing that didn't solve the problem. I measured the coil resistances and found my secondary winding was high resistance - 25.2kOhms instead of 11.5-18.5kOhms. It also appeared to be missing that 1kOhm resistor required for the tacho. Bought and installed a new coil, and this one does have that resistor. Nothing solved the problem, but glad I did them anyway to make sure they don't fault on me in future.

Here are a couple of photos worth keeping open, courtesy of other members of this site who posted them originally. I'll be referring to them as I go.
Please ignore the cylinder numbers in the first photo - they aren't the same as in my car, so I'd recommend taking photos before starting. Also, wire colours don't appear to be the same, but positions in their pins do.
http://i18.photobucket.com/albums/b120/emxsix/Diagrams/94distydiagnosis_zps06be87ad.jpg
http://ups.mazda626.net/images_monthly_04_2014/img-377216-1-G-16.jpg

Summary of how the ignition system works and what you're actually testing for:
The coil is supposed to be always provided with 12V with the ignition on. There are two engine speed sensors in the distributor (hall effect sensors) which provide electrical pulses back to the PCM (powertrain control module) which is the engine computer. The computer decides, based on the position of the engine in its rotation and other parameters, when to send a pulse back to the distributor to fire the spark (it can finely change spark timing). These pulses are fed to pin f of the second picture, which is the base of a transistor called the ignitor. When this transistor receives the pulse, it turns on and allows the coil to have a complete circuit, creating the spark. The two speed sensors send their pulses back to the PCM through pins 3 and 4 on the big connector (in the first picture) at the distributor end and pins c and d in the second picture.

Firstly test for good 12V supply and earth:
In the first paragraph of the first photo, you're checking that the coil is provided with 12V when the ignition is on. Pin 3 of the small plug is terminal C in the second picture.
The second paragraph in the first picture is to check for a good ground connection for the coil. A better way would be to use a multimeter and make sure there's a low resistance (like an ohm or less) between pin 5 and the negative battery terminal, as a test light would still shine even if there was a slightly resistive earth connection.

If either of these two tests don't pass, check fuses and wire continuity.

Next tests - are the engine speed sensors working?
For these tests I left both plugs plugged in and just poked my test probe through the insulation to test them. Most of the wires had partially exposed copper where the wire was bent anyway, so it wasn't hard. You can either use a test lamp or a multimeter which has a Hz (frequency) setting.
Take your test light and attach the clamp to the positive battery terminal. Touch the test light to pin 3 of the big connector in the first photo and get someone to crank the engine. This should cause the test light to flash while the engine turns over. Do the same with pin c and the same should happen. With one of them the light will flash fast, the other slow (one is the speed sensor with 6 pulses per rotation, the other is 1 pulse per rotation). If one doesn't flash, it's possible the hall effect sensor is no good and the engine is not receiving a signal of the engine's speed from that sensor.

Next test - continuity of speed sensor wires between distributor and PCM:
Now you know that the sensors work fine, let's check continuity of the wires to the PCM. You need access to the PCM which is underneath the radio. Instead of rigging wires between the engine bay and the cabin, plug your multimeter probe into the back of the +12V (red wire) in the plug to the PCM, and change your multimeter to amps. Then you can clamp your test light onto the other multimeter probe, giving it 12V and allowing you to test for earths.
Now you can do the exact same test as before but inside the cabin (and you can crank the engine yourself). Find the two speed sensor wires by colour (colours should be distinct) and touch your test probe to one at a time, cranking the engine each time. The light should flash as before. If it does, you have good contunuity between the distributor and the PCM.

Next step: is the PCM sending a pulse back?
Follow the third paragraph of the first picture to see if a pulse from the PCM is getting back to the distributor. If not, find that wire at the PCM and do the same test to see if it's just a wire continuity fault between the PCM and the distributor.

My PCM appeared not to be giving a signal back to the distibutor so I removed it and opened it up. I found some corrosion on one of the PCBs which appears to have been caused by a capacitor leaking. It hadn't exploded but was misshapen at the bottom, and there was corrosion right down one of its pins to the PCB. I measured its capacitance, which was still pretty good, but I replaced it anyway. While it was off the board, I gave the board a clean with PCB cleaner and plastic brush. The damage was pretty deep and most of the corrosion wouldn't come off. I tested continuity and found two tracks had been corroded away, so I jumpered them with wires.

I put the PCM back in the car and away she went - no problems after that point. I tested to confirm I should have got a signal out of the PCM (I was using the multimeter frequency setting) and I was getting around 50Hz at idle. While cranking it would show 14Hz. I have since considered pulling the PCM back out and replacing all the capacitors on the board just to prevent this happening again. I suspect that the battery had gone flat due to a short circuit made by the capacitor leaking, and then wouldn't start after that due to the damage.

I am quite relieved, too, because naturally I looked around for second hand replacement PCMs and holy guacamole there are dozens of (seemingly) different kinds. Mine has KL28 18 881E written on it and I haven't seen a single one available of that type. Anyone know how cross compatible different types are? If I have a manual do I need one from a manual?

Could someone also tell me if the HEI mod is a performance upgrade (ie provides a stronger spark) or is just used as a replacement ignitor module?
 

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HEI mod is a cheap method of replacing the ignitor within the distributor, it does not provide any increased spark power.
 

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Hi guys,

I see that ignition problems seem to be one of the commonest things that go wrong with MX-6s. Having recently had this issue myself and successfully solved it, I thought I should share what was wrong and how I went about it. I should confess, it was greatly due to having this forum site to refer to that I was able to do it so easily. Also, the problem that I had may not be the same as what others have, but I'll go through the general fault finding order that I went through.

A few weeks ago, after just a few months of owning it, I went to start my '93 MX-6 and it mysteriously had a flat battery. It had gone flat on its own far too quickly and there was no reason for it. So I charged the battery and suspected a current drain somewhere. This problem happened again just once but then it stopped. I was still using the car during this time.

The day or two after this episode I tried to start the car but would do is turn over. It had worked faultlessly until then, but it would not start. The battery soon ran flat and with a jump start, it suddenly fired again.

Somewhat randomly, the car would either start or not start. With a jump start it seemed to start more often. I quickly concluded there was no spark and started reading up on mx6.com and found how common ignition problems are. The problem I had is best summed up by the fact the car wouldn't start, but once it was running it wouldn't stop running. Unfortunately this car doesn't have an engine check light, so I was unable to read OBDI codes from it.

So to start I opened the distributor and all seemed well, no unnecessary wear or damage. Unfortunately, an earthing wire seemed to just break off the back, but repairing that didn't solve the problem. I measured the coil resistances and found my secondary winding was high resistance - 25.2kOhms instead of 11.5-18.5kOhms. It also appeared to be missing that 1kOhm resistor required for the tacho. Bought and installed a new coil, and this one does have that resistor. Nothing solved the problem, but glad I did them anyway to make sure they don't fault on me in future.

Here are a couple of photos worth keeping open, courtesy of other members of this site who posted them originally. I'll be referring to them as I go.
Please ignore the cylinder numbers in the first photo - they aren't the same as in my car, so I'd recommend taking photos before starting. Also, wire colours don't appear to be the same, but positions in their pins do.
http://i18.photobucket.com/albums/b120/emxsix/Diagrams/94distydiagnosis_zps06be87ad.jpg
http://ups.mazda626.net/images_monthly_04_2014/img-377216-1-G-16.jpg

Summary of how the ignition system works and what you're actually testing for:
The coil is supposed to be always provided with 12V with the ignition on. There are two engine speed sensors in the distributor (hall effect sensors) which provide electrical pulses back to the PCM (powertrain control module) which is the engine computer. The computer decides, based on the position of the engine in its rotation and other parameters, when to send a pulse back to the distributor to fire the spark (it can finely change spark timing). These pulses are fed to pin f of the second picture, which is the base of a transistor called the ignitor. When this transistor receives the pulse, it turns on and allows the coil to have a complete circuit, creating the spark. The two speed sensors send their pulses back to the PCM through pins 3 and 4 on the big connector (in the first picture) at the distributor end and pins c and d in the second picture.

Firstly test for good 12V supply and earth:
In the first paragraph of the first photo, you're checking that the coil is provided with 12V when the ignition is on. Pin 3 of the small plug is terminal C in the second picture.
The second paragraph in the first picture is to check for a good ground connection for the coil. A better way would be to use a multimeter and make sure there's a low resistance (like an ohm or less) between pin 5 and the negative battery terminal, as a test light would still shine even if there was a slightly resistive earth connection.

If either of these two tests don't pass, check fuses and wire continuity.

Next tests - are the engine speed sensors working?
For these tests I left both plugs plugged in and just poked my test probe through the insulation to test them. Most of the wires had partially exposed copper where the wire was bent anyway, so it wasn't hard. You can either use a test lamp or a multimeter which has a Hz (frequency) setting.
Take your test light and attach the clamp to the positive battery terminal. Touch the test light to pin 3 of the big connector in the first photo and get someone to crank the engine. This should cause the test light to flash while the engine turns over. Do the same with pin c and the same should happen. With one of them the light will flash fast, the other slow (one is the speed sensor with 6 pulses per rotation, the other is 1 pulse per rotation). If one doesn't flash, it's possible the hall effect sensor is no good and the engine is not receiving a signal of the engine's speed from that sensor.

Next test - continuity of speed sensor wires between distributor and PCM:
Now you know that the sensors work fine, let's check continuity of the wires to the PCM. You need access to the PCM which is underneath the radio. Instead of rigging wires between the engine bay and the cabin, plug your multimeter probe into the back of the +12V (red wire) in the plug to the PCM, and change your multimeter to amps. Then you can clamp your test light onto the other multimeter probe, giving it 12V and allowing you to test for earths.
Now you can do the exact same test as before but inside the cabin (and you can crank the engine yourself). Find the two speed sensor wires by colour (colours should be distinct) and touch your test probe to one at a time, cranking the engine each time. The light should flash as before. If it does, you have good contunuity between the distributor and the PCM.

Next step: is the PCM sending a pulse back?
Follow the third paragraph of the first picture to see if a pulse from the PCM is getting back to the distributor. If not, find that wire at the PCM and do the same test to see if it's just a wire continuity fault between the PCM and the distributor.

My PCM appeared not to be giving a signal back to the distibutor so I removed it and opened it up. I found some corrosion on one of the PCBs which appears to have been caused by a capacitor leaking. It hadn't exploded but was misshapen at the bottom, and there was corrosion right down one of its pins to the PCB. I measured its capacitance, which was still pretty good, but I replaced it anyway. While it was off the board, I gave the board a clean with PCB cleaner and plastic brush. The damage was pretty deep and most of the corrosion wouldn't come off. I tested continuity and found two tracks had been corroded away, so I jumpered them with wires.

I put the PCM back in the car and away she went - no problems after that point. I tested to confirm I should have got a signal out of the PCM (I was using the multimeter frequency setting) and I was getting around 50Hz at idle. While cranking it would show 14Hz. I have since considered pulling the PCM back out and replacing all the capacitors on the board just to prevent this happening again. I suspect that the battery had gone flat due to a short circuit made by the capacitor leaking, and then wouldn't start after that due to the damage.

I am quite relieved, too, because naturally I looked around for second hand replacement PCMs and holy guacamole there are dozens of (seemingly) different kinds. Mine has KL28 18 881E written on it and I haven't seen a single one available of that type. Anyone know how cross compatible different types are? If I have a manual do I need one from a manual?

Could someone also tell me if the HEI mod is a performance upgrade (ie provides a stronger spark) or is just used as a replacement ignitor module?
Hi guys,

I see that ignition problems seem to be one of the commonest things that go wrong with MX-6s. Having recently had this issue myself and successfully solved it, I thought I should share what was wrong and how I went about it. I should confess, it was greatly due to having this forum site to refer to that I was able to do it so easily. Also, the problem that I had may not be the same as what others have, but I'll go through the general fault finding order that I went through.

A few weeks ago, after just a few months of owning it, I went to start my '93 MX-6 and it mysteriously had a flat battery. It had gone flat on its own far too quickly and there was no reason for it. So I charged the battery and suspected a current drain somewhere. This problem happened again just once but then it stopped. I was still using the car during this time.

The day or two after this episode I tried to start the car but would do is turn over. It had worked faultlessly until then, but it would not start. The battery soon ran flat and with a jump start, it suddenly fired again.

Somewhat randomly, the car would either start or not start. With a jump start it seemed to start more often. I quickly concluded there was no spark and started reading up on mx6.com and found how common ignition problems are. The problem I had is best summed up by the fact the car wouldn't start, but once it was running it wouldn't stop running. Unfortunately this car doesn't have an engine check light, so I was unable to read OBDI codes from it.

So to start I opened the distributor and all seemed well, no unnecessary wear or damage. Unfortunately, an earthing wire seemed to just break off the back, but repairing that didn't solve the problem. I measured the coil resistances and found my secondary winding was high resistance - 25.2kOhms instead of 11.5-18.5kOhms. It also appeared to be missing that 1kOhm resistor required for the tacho. Bought and installed a new coil, and this one does have that resistor. Nothing solved the problem, but glad I did them anyway to make sure they don't fault on me in future.

Here are a couple of photos worth keeping open, courtesy of other members of this site who posted them originally. I'll be referring to them as I go.
Please ignore the cylinder numbers in the first photo - they aren't the same as in my car, so I'd recommend taking photos before starting. Also, wire colours don't appear to be the same, but positions in their pins do.
http://i18.photobucket.com/albums/b120/emxsix/Diagrams/94distydiagnosis_zps06be87ad.jpg
http://ups.mazda626.net/images_monthly_04_2014/img-377216-1-G-16.jpg

Summary of how the ignition system works and what you're actually testing for:
The coil is supposed to be always provided with 12V with the ignition on. There are two engine speed sensors in the distributor (hall effect sensors) which provide electrical pulses back to the PCM (powertrain control module) which is the engine computer. The computer decides, based on the position of the engine in its rotation and other parameters, when to send a pulse back to the distributor to fire the spark (it can finely change spark timing). These pulses are fed to pin f of the second picture, which is the base of a transistor called the ignitor. When this transistor receives the pulse, it turns on and allows the coil to have a complete circuit, creating the spark. The two speed sensors send their pulses back to the PCM through pins 3 and 4 on the big connector (in the first picture) at the distributor end and pins c and d in the second picture.

Firstly test for good 12V supply and earth:
In the first paragraph of the first photo, you're checking that the coil is provided with 12V when the ignition is on. Pin 3 of the small plug is terminal C in the second picture.
The second paragraph in the first picture is to check for a good ground connection for the coil. A better way would be to use a multimeter and make sure there's a low resistance (like an ohm or less) between pin 5 and the negative battery terminal, as a test light would still shine even if there was a slightly resistive earth connection.

If either of these two tests don't pass, check fuses and wire continuity.

Next tests - are the engine speed sensors working?
For these tests I left both plugs plugged in and just poked my test probe through the insulation to test them. Most of the wires had partially exposed copper where the wire was bent anyway, so it wasn't hard. You can either use a test lamp or a multimeter which has a Hz (frequency) setting.
Take your test light and attach the clamp to the positive battery terminal. Touch the test light to pin 3 of the big connector in the first photo and get someone to crank the engine. This should cause the test light to flash while the engine turns over. Do the same with pin c and the same should happen. With one of them the light will flash fast, the other slow (one is the speed sensor with 6 pulses per rotation, the other is 1 pulse per rotation). If one doesn't flash, it's possible the hall effect sensor is no good and the engine is not receiving a signal of the engine's speed from that sensor.

Next test - continuity of speed sensor wires between distributor and PCM:
Now you know that the sensors work fine, let's check continuity of the wires to the PCM. You need access to the PCM which is underneath the radio. Instead of rigging wires between the engine bay and the cabin, plug your multimeter probe into the back of the +12V (red wire) in the plug to the PCM, and change your multimeter to amps. Then you can clamp your test light onto the other multimeter probe, giving it 12V and allowing you to test for earths.
Now you can do the exact same test as before but inside the cabin (and you can crank the engine yourself). Find the two speed sensor wires by colour (colours should be distinct) and touch your test probe to one at a time, cranking the engine each time. The light should flash as before. If it does, you have good contunuity between the distributor and the PCM.

Next step: is the PCM sending a pulse back?
Follow the third paragraph of the first picture to see if a pulse from the PCM is getting back to the distributor. If not, find that wire at the PCM and do the same test to see if it's just a wire continuity fault between the PCM and the distributor.

My PCM appeared not to be giving a signal back to the distibutor so I removed it and opened it up. I found some corrosion on one of the PCBs which appears to have been caused by a capacitor leaking. It hadn't exploded but was misshapen at the bottom, and there was corrosion right down one of its pins to the PCB. I measured its capacitance, which was still pretty good, but I replaced it anyway. While it was off the board, I gave the board a clean with PCB cleaner and plastic brush. The damage was pretty deep and most of the corrosion wouldn't come off. I tested continuity and found two tracks had been corroded away, so I jumpered them with wires.

I put the PCM back in the car and away she went - no problems after that point. I tested to confirm I should have got a signal out of the PCM (I was using the multimeter frequency setting) and I was getting around 50Hz at idle. While cranking it would show 14Hz. I have since considered pulling the PCM back out and replacing all the capacitors on the board just to prevent this happening again. I suspect that the battery had gone flat due to a short circuit made by the capacitor leaking, and then wouldn't start after that due to the damage.

I am quite relieved, too, because naturally I looked around for second hand replacement PCMs and holy guacamole there are dozens of (seemingly) different kinds. Mine has KL28 18 881E written on it and I haven't seen a single one available of that type. Anyone know how cross compatible different types are? If I have a manual do I need one from a manual?

Could someone also tell me if the HEI mod is a performance upgrade (ie provides a stronger spark) or is just used as a replacement ignitor module?
Well I cannot see your pics to see what the heck your talking about, I am disabled and mine started draining battery, then running on 4 cylinders now not at all, I replaced coil in my 93 mx6 v6 2 months back after transplant surgery, it ran fine for a while till started running on 4 cylinders, I really need help as I'm giving this car to my grandson b4 I pass, and the clock is ticking fast.Help will be greatly appreciated. Dave h
 
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