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Doug
Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 8538
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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Mitsubishi Mirage ES: 01 MIRAGE, 1.8. SETS PO300. WON'T SET

Customer Question

01 MIRAGE, 1.8. SETS PO300. WON'T SET SPECIFIC CYLINDER MISFIRE. PROBLEM IS INTERMITTENT. HAVE ONLY SENSED AT IDLE ,NOT UNDER LOAD. HAVE MONITORED PIN 3 FROM COILS , INJECTORS,CAM & CRANK SENSORS AND RUNNING VACUUM WITH NO CHANGE WHEN OCCURRING. WHILE MONITORING IGNITION FAILURE SENSOR PATTERN SEEMS TO CHANGE FROM NARROW CLIPPED 8 VOLT SQUARE WAVE TO A CLEAN 5V SQUARE WAVE. QUESTION 1 IS IT NORMAL FOR PATTERN TO CHANGE & 2,IS IT EVEN POSSIBLE FOR THIS SENSOR TO CAUSE WHAT FEELS LIKE A SINGLE CYLINDER MISFIRE ?(HAS NEW PLUGS & WIRES)
Submitted: 6 months ago.
Category: Mitsubishi
Expert:  Doug replied 6 months ago.
Hi, I would expect you are talking about the PCM output wire going into the ignition failure sensor. It is not normal to see 8V here, the driver is only a 5V driver. If you are seeing 8V I would suspect there might be an issue with the voltage regulator in the alternator or an internal defect in the PCM. There isn't any way under normal conditions that the 5V driver could push an 8V waveform.The ignition failure sensor is not likely to cause any sort of sensation like you describe. The ignition failure sensor is just a very expensive/glorifed fuse. If there is a malfunction (specifically high draw on a coil is most common), the ignition failure sensor cuts power to the coils so they can no longer fire. If there is a short, it will blow out the failure sensor instead of damaging the PCM.If you are seeing random misfire faults and no signs of it narrowing to a single cylinder you are in the right line of thought with devices that affect all cylinders at once, just the ignition failure sensor isn't likely to be it.I would be curious about the fuel pressure while running and under load, the retained pressure after key-off, the engine compression (Across the board), checking for blockages in the exhaust and the MAF readings (running and under load). Those are your biggest suspects when dealing with a random misfire on this model with no signs of narrowing to individual cylinders.

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