MMiskoe Posted August 15, 2021 Report Share Posted August 15, 2021 Looking for some help on diagnosis of an ignition issue that cropped up at the VIR 24 hour. 1994 Miata, stock electronics and engine management system. Dash board has been removed and gauges rewired. Car started the race and ran at low RPM for 60+ minutes due to rain and an extended safety car period. Once we went back green it did 2 laps before it overheated and destroyed one of the coils. Change coils, send it out, gets about 20 minutes of run time, same issue. Changed again, same scenario. At that point we were out of ideas and coils so we packed up. When they fail, the coils are too hot to touch and some of them physically cracked near the plug when they come off the car. There is no indication of problem before the car simply goes to two cylinders. We assumed that something was over-driving the coils and they were acting as if they were passing currently 100% of the time which they aren’t really capable of and thus they over heat. We got our hands on an oscilloscope and measured the signal from the ECU to the coil. The attached picture shows the racecar and a streetcar (1999). We also tested a different racecar which looked nearly identical to the streetcar, so we know that the coil signal in the racecar is wrong. So we started swapping parts. ECU. Cam angle sensor. Alternator. Un-plug the fuel pump while it is running. Check the signal at the ECU, not at the coil pack. Unplug all data systems, tachometer, lighting, cool suit. None of these things had any impact on the signal we were reading on the scope. All the grounds have been looked at and appear to be sound. We were fully expecting that the ECU, CAS or alt change would have made an impact. We’re at a loss as to what could be causing this. The car ran fine last summer and last fall. This spring it did a test day where we were on track for 10-15 minutes, then off track for twice that time all day. We don't know it was a problem then because the run time was short, possibly giving the coils time to cool down. Quote Link to comment Share on other sites More sharing options...
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