No Spark from Upper Coil Outlets on 1990 Subaru Legacy 2.2: Causes and Diagnosis

The ignition system is one of those parts of a car you don’t think about–until it starts acting up. And when it does, it can turn a perfectly reliable engine into a sputtering, no-start mystery. On a 1990 Subaru Legacy 2.2, one especially aggravating scenario is seeing spark on only the *lower* coil outlets while the *upper* ones stay dead. It’s the kind of thing that makes people throw parts at the car out of sheer frustration. But this problem usually has a clear explanation once you understand what’s supposed to happen in the first place.

What’s supposed to be happening

The ’90 Legacy 2.2 uses a distributor-based ignition setup with a coil pack that feeds spark to the cylinders. Think of the coil pack as the “spark factory.” It creates the high voltage needed for ignition, and the system routes that voltage through the distributor to the correct cylinder at the correct time.

Those coil outlets aren’t just random towers–they’re paired to fire specific cylinders. Typically, the lower outlets handle one pair of cylinders and the upper outlets handle the other pair. So if the lower pair is firing and the upper pair is totally quiet, the engine is effectively trying to run on half its normal spark output. That can mean misfires, rough idle, hesitation, or an engine that won’t stay running at all.

Why this happens in the real world

When only one set of outlets is sparking, the cause is usually something that’s preventing *one half of the system* from being triggered or from delivering its output. The most common culprits are:

1. A failing coil pack

Coil packs can partially fail. It’s not always “works” or “doesn’t work.” Internal windings can crack, short, or break down so that one side still produces spark while the other side can’t.

1. Ignition control module (ICM) issues

The ICM is basically the traffic controller. It tells the coil when to fire. If it’s weak, damaged, or sending an incomplete signal, you can end up with one coil circuit firing and the other not.

1. Wiring or connector problems

Old Subarus live long lives, and heat, vibration, and moisture take their toll. A corroded connector, a broken wire inside the insulation, or a poor pin fit can kill the signal to one side of the coil pack and make it look like a “bad coil.”

1. Crank/cam sensor trouble

The ECU relies on timing signals from sensors like the crankshaft and camshaft position sensors. If those signals are missing or distorted, the ECU/ICM may not trigger coil firing properly–sometimes in a way that looks like only part of the coil pack is dead.

1. Bad grounds

Grounds are the boring part nobody wants to check, which is exactly why they cause so many headaches. A weak or corroded ground can create strange, inconsistent ignition behavior–including selective spark failure.

How a good tech actually diagnoses it

Pros don’t guess–they narrow it down. Usually the process looks like this:

• Start with a careful visual inspection (cracked coil housing, carbon tracking, loose plugs, green crusty connectors, rubbed-through wiring).
• Verify power and ground at the coil and module.
• Use a multimeter (and sometimes an oscilloscope) to confirm whether the coil is being commanded to fire and whether it’s producing output correctly.
• If the trigger signal is missing or unstable, move upstream: ICM checks, then sensor signal checks.

That step-by-step approach matters because it prevents the classic trap: replacing a coil pack when the real issue is a broken wire or a failing module.

The mistakes that waste the most time (and money)

The biggest one is assuming “no spark = bad coil.” Coil packs do fail, yes–but they’re not the only player in the chain. Another common miss is ignoring wiring because it “looks fine.” A wire can be broken internally and still appear perfect from the outside.

And finally, people often underestimate grounding problems. A single poor ground can mimic several different failures and send you on a wild goose chase.

Tools and parts you’ll usually deal with

• Tools: multimeter, scan tool (if applicable), sometimes an oscilloscope, test light
• Parts/categories: coil pack, ignition control module, wiring/connector repair items
• Sensors: crankshaft position sensor, camshaft position sensor (depending on the system layout)

Bottom line

If your 1990 Subaru Legacy 2.2 is only sparking from the lower coil outlets, it’s a strong sign that one side of the ignition system isn’t being triggered or can’t deliver voltage. The coil pack might be the problem–but so could the ignition module, wiring, sensors, or even a simple ground issue. The fastest way to fix it (and keep your sanity) is to diagnose it in order, instead of swapping parts and hoping you get lucky.