Experiencing a perplexing issue with a 93 Subaru Impreza and scratching your head? I recently ran into a strange starting problem with what I believe is a similar year Subaru, and it has led me down a rabbit hole of diagnostics. Initially, the engine wouldn’t start, and the voltage seemed a bit low, although the engine cranked over just fine. This was despite having a brand new battery and alternator installed. The cranking sound was unusual, a kind of “hollow” sound that often points to a timing belt being off a tooth or two.
Naturally, the timing belt was the first thing I checked. I reset the belt, and while it was indeed off by one tooth – likely an installation error rather than slippage – correcting it didn’t solve the starting issue. So, timing wasn’t the culprit in this case.
Moving on to electrical checks, I turned the key to the ‘on’ position. The Check Engine Light (CEL) illuminated for only about half a second before switching off. Crucially, the system wouldn’t enter test mode or allow me to pull any diagnostic codes. Suspecting a relay issue, I swapped the Ignition relay, but there was no change in behavior. I then cleaned the connection of the Fusible link that supplies voltage to the Ignition relay, again with no improvement. At this point, the battery was getting quite low from repeated cranking attempts, so jumper cables were connected to provide a boost.
After charging for a while, I tried starting again. This time, the CEL was lighting up, almost steadily, or at least more consistently than before. However, it was still blinking on and off randomly, not in the rhythmic pattern of test mode or error code flashes (I’m familiar with those). Another start attempt – and this time the engine struggled, but eventually caught and started. Interestingly, just before it started, the cranking sound reverted to a normal “cachuga-chuga” rhythm, and then it fired up. I shut it down and tried to restart immediately. Now, it was back to cranking with that hollow sound, and wouldn’t start, and the CEL was gone again. It seemed like the ECU was cutting out fuel and spark.
After a few more tries, the engine once again started sounding normal during cranking, the CEL flickered back to life (still erratic), and it fired up again. Since then, it has started consistently each time.
This intermittent issue has me wondering if anyone has encountered an ECU failing in this manner on a 93 Subaru Impreza or similar models. I’ve seen ECUs fail to light the CEL at all, but never seen one behave so erratically, seemingly tripping out and then recovering. My next step is to try swapping in a known good ECU to see if that resolves the problem. I even managed to capture a video of the strange CEL behavior.
Has anyone in the community experienced a similar ECU failure mode with these older Subaru Impreza models, particularly those around 1993 that might be early OBD2 or pre-OBD2? Any insights or suggestions would be greatly appreciated.
