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Electical problems with my 93

Old 01-06-19, 10:10 PM
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Electical problems with my 93

I'm having a few issues with my 93 at the moment and after searching endlessly and testing via the FSM, I'm still left wondering.
The car originally was a auto, with the Bose system but has since been swapped to a MT, along with a MT harness and base instrument / dash harness.

My first issue is lack of spark on the T2 coil. Plugging the T1 connector into the T2 coil gives spark, so the coil appears to be ok. I have power at all coil connectors and continuity between all coils and the ignitor connector. Trying a spare ignitor, I get the same result - no spark from the T2 coil, but great spark from all others. Am I unlucky enough to have two bad ignitors in a row that have failed in the exact same way, or is my PFC damaged and not signaling the ignitor?

Second issue is the lack of interior lighting. I have no dash or instrument backlighting at any key position or any setting of headlights. The odometer does illuminate and display mileage, also the ignition key light works. Headlights high / low work, retractors work, running and stop lights are good, signals are good. The hazard lights are inoperable, along with no blower motor. The vent selector switch does seem to operate the servo, I can hear it move the doors in the heater box when I change the switch position.

Last edited by DPeanut; 01-06-19 at 10:30 PM.
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Old 01-06-19, 11:15 PM
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I'm not sure how you could easily test for an ECU ignition signal without the car running, but pins 1G,1J, are trailing ECU signals, and 1H is leading signal, .2v to .5v ref voltages on oem Mazda ecu.
I think you would need to get a hold of a true rms O-scope meter to measure those signals while engine is running.
If you could safely plug in a stock ECU to only idle the car at 850 rpm, it might be an easier way of ruling out a broken Apexi ECU ignition signal path ?
No idea on HVAC components and interior lights other than checking if they might all share a common fuse or circuit ?
I guess you have already checked for blown fuses under dash and next to battery ?
On hazard lights, are you referring to 4 way flashers ? If yes, I would try puling and carefully re-inserting all connectors on long black ECU #2 box, after checking all pins are straight, ahead of driver's door in footwell.
The 93 or 94 wiring diagram has a schematic of ECU #2 circuits I think. If you can't find it , I'll post it.
Other than that, ECU #2 itself or possibly your switch contacts, not sure what else to suggest checking 1st.
Good luck !

Last edited by Blk 93; 01-06-19 at 11:31 PM.
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Old 01-07-19, 12:06 AM
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At the moment, I don't have the UIM installed so I wouldn't be able to fire it. I do have the stock ECU kicking around for it so that could be another thing to try, just to see if I am able to get spark on the rear trailing coil.
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Old 01-07-19, 01:36 PM
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How are you testing for spark?

Could be a problem with the coil pack harness, that's a common problem and Mazda updated the harness. If your harness has a ground on it that connects to one of the coil packs it's the OLD harness. The new one is about $80 or so and DOES NOT have a ground wire.

The shop manual has a procedure for testing the coils with a meter, I've found that method to be good and a bad coil will definitely fail that test.

Do you have any sort of ignition mods or anything?

Also +1 to testing with stock ECU. It's possible the output transistor for that coil is burned out on the PFC. Not a common problem by any stretch, though, but worth testing.

Lighting problems you need to check all your fuses first.

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Old 01-07-19, 05:23 PM
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Corrected the lack of spark in the T2 coil. Same result of no spark on T2 when testing with the stock ECU. I rechecked continuity between the ECU and igniter connectors with probes - no continuity. I removed the brown / black terminals on both the igniter connector and ECU connector and checked for continuity using alligator clips - continuity. I replaced both terminals and now have spark on the T2 coil.

For the interior lights it seems that the back light for the odometer is different between headlights of and on. All fuses have been checked in all fuse panels, I have 12V at the dimmer switch connector with the key on. I beleive that my instrument backlighting issue is coming from the mosfet inside. The potentiometer tests out in spec, and all other components appear to be fine. When I am home later I'm going to pull up the data sheet and test it.
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