Encountering a perplexing issue with a 1993 Subaru Impreza recently? Let’s delve into a peculiar starting problem that surfaced, potentially linked to the OBD2 system and ECU functionality of this classic vehicle. This case study explores a no-start condition characterized by unusual Check Engine Light (CEL) behavior and inconsistent engine cranking.
Initially, the Subaru presented a no-start scenario. Despite a healthy cranking speed, indicative of a functioning starter and a relatively new battery and alternator, the engine failed to ignite. A preliminary check revealed a slightly low voltage, but not critically so. Intriguingly, the engine exhibited a “hollow” cranking sound, often associated with timing belt misalignment. Upon inspection, the timing belt was indeed off by a single tooth, possibly a result of incorrect installation rather than slippage. However, correcting the timing belt issue did not resolve the core problem, indicating a deeper underlying fault.
Moving towards electrical diagnostics, attention shifted to the CEL behavior upon key ignition. The CEL illuminated only momentarily for about half a second before extinguishing, failing to enter the diagnostic test or read mode. Suspecting a relay issue, the ignition relay was swapped, but this yielded no change. Further investigation involved cleaning the fusible link connection supplying voltage to the ignition relay, again with no improvement. Repeated cranking attempts began to drain the battery, necessitating jump leads for supplemental power.
After charging the battery, a subtle shift in CEL behavior was observed. The CEL became more consistently illuminated, albeit with a random blinking pattern, distinctly different from the rhythmic flashes of test mode or diagnostic codes. Another start attempt resulted in labored cranking, but eventually, the engine sputtered to life. Notably, just before starting, the cranking sound reverted to a normal, healthy rhythm. Subsequent engine shutdown and restart attempts reintroduced the “hollow” cranking sound and no-start condition, accompanied by the absent CEL. This suggested an intermittent ECU issue, potentially cutting off fuel and spark delivery.
Further trials revealed an unpredictable pattern: sometimes the engine would crank normally and start with a more stable (though still erratic) CEL, and other times it would revert to the no-start, hollow crank, and absent CEL state. Since these incidents, the vehicle has started consistently, adding to the mystery.
The central question arising from these observations is whether anyone has encountered a similar ECU failure mode in a 1993 Subaru Impreza or comparable OBD2 system. While ECU failures leading to a completely unlit CEL are known, this scenario of intermittent CEL operation and fluctuating starting behavior points towards a potentially unique ECU malfunction. The next diagnostic step involves testing with a replacement ECU to ascertain if this resolves the issue. Community insights and experiences with similar symptoms would be invaluable in confirming this suspicion and guiding further troubleshooting.
