I’m encountering a strange problem with a 1993 Subaru Impreza. This issue is new to me, and I’m hoping someone in the community might have seen something similar.
The car intermittently refuses to start. Initially, I noticed the engine cranking sounded “hollow,” almost like a timing belt issue – reminiscent of when the belt is off by a tooth or two. My first thought was to check the timing belt. I reset it, finding it was indeed a tooth off, likely from a previous installation error rather than slippage. However, correcting the timing belt didn’t solve the starting problem.
Next, I started looking at the electrical system. When I turn the key to the ‘on’ position, the check engine light (CEL) illuminates for only about half a second before going out. Crucially, it won’t enter test mode or allow me to read any diagnostic codes. I swapped the ignition relay, suspecting a potential relay issue, but this made no difference. I also cleaned the fusible link connection that supplies voltage to the ignition relay, again with no change in the symptoms.
During this process, the battery voltage dropped considerably from repeated cranking, even though it’s a new battery, and the alternator is also new. We connected jumper cables to provide additional power. After charging for a while, I tried starting again. This time, the CEL behaved differently – it was almost constantly lit, or at least much more so than before. However, it was still blinking erratically, not in the rhythmic pattern of test mode or error code flashes which I am familiar with.
Attempting to start the engine, it struggled initially but eventually caught and started. Before it started, the cranking sound returned to a normal, healthy sound. I shut it off and tried to restart immediately. Now, the cranking sound was hollow again, and the engine wouldn’t start, and the CEL was off once more. It feels like the ECU is cutting off fuel and spark.
After a few more attempts, the engine started sounding normal again, the CEL illuminated (though still flickering strangely), and the car fired up and ran well. Since that point, it has started consistently each time.
My primary question for the community is: has anyone experienced an ECU failure mode like this in a 1993 Subaru Impreza? I’ve seen ECUs fail in ways that prevent the CEL from lighting up at all, but never this intermittent and erratic behavior. My next step is to try swapping in a known good ECU to see if that resolves the problem. I plan to record a video of the CEL behavior to document this unusual issue.
Any insights or experiences you can share would be greatly appreciated. Thanks in advance for your help!
Edited by TechCarUSA Expert
