Car only sparking on 2 and 4 cylinder

Hi,

working on a 2010 subaru wrx brand new motor installed, the car is only firing spark on 2 and 4 but not one 1 and 3. Looks like 1 and 3 fire first from what manuals say, 3 wire coil measures out 12 volts and a solid ground. What confuses me is that the switched ignition shows a slight ground on 4 coils when the key is off and increases when the key is on. Does this rule out cam sensors being bad? The car does run on starter fluid and continues if we feed it. Pulled plugs on 1 and 3 and it looks like they have never fired ever.

I’m not sure I’m fully understanding. So just to be clear....
When it runs on starter fluid does it sound like it’s running on just 2 cylinders? Does the car start without starter fluid?

No spark on 2 cylinders should still start just run very bad.

Forgive my skepticism but if it is running fine with starter fluid I think you’re barking up the wrong chain by chasing spark. I would strongly suggest going after fuel.

Hi thanks for the reply, yeah I had coils 1 and 3 out and it runs on starter fluid with only 2 and 4 hooked up. I checked for spark on 1 and 3 with a spark tester and no luck. It measures for ground and 12 volts.

Gotcha! I’m not sure what equipment you have available so I’m going to suggest labeling the coils and swapping the known good coil in place of the coil that is not firing.

See if the spark or lack of spark follows. If it does then it’s the coil if not more testing will be required.

1-3-2-4 firing order.

ISTR hearing of this issue before on Scoobies and it was crank sensor &. trigger wheel related.

I have swapped coils and the no spark issue does not follow. What’s strange for me is that cylinders 2-4 spark but not 1-3. I did however unplug the cam sensor near 1 since there’s 4 total and it did not stop 2 and 4 from sparking that maybe they’re isolated.

Turbo or Non-turbo?
What is your transmission SN? Ill try to pull some diagrams
I want to make sure I’m looking at the right diagrams.

Hi it’s an 08 sti manual 6 speed. Getting strong 12 volts and .2 ohm ground. With the switched signal I am seeing a ground when the key is on but it’s stronger then the ignition is on but does not change brightness like it should on the videos.

Cylinders 1 and 3 are on the passenger side and do not fire even swapping coils. I did take out the exhaust cam sensor to see if that effects spark for the drivers side and it doesn’t not stop 2 and 4 from firing.

So doing some more testing, I am getting coil signal of 4.5 volts to the 2 and 4 but on 1 and 3 I am only getting .8 volts I tested it at the ecm and same readings. Please any help would be greatly appreciated.

AvBacon wrote: So doing some more testing, I am getting coil signal of 4.5 volts to the 2 and 4 but on 1 and 3 I am only getting .8 volts I tested it at the ecm and same readings. Please any help would be greatly appreciated.

Which wires?
Red is B+ for all coils
Coil 1 and 3 have a black wire for the ground.
Coil 2 and 4 have a black and white for the ground.
Coil 1 control should be grey
Coil 3 control should be brown and yellow

Being that both coils that aren’t firing share a ground, I would use a jumper to provide a known good ground or scope the ground and see if it’s a bad ground (being pulled up). It’s more likely that a shared ground is bad than 2 separate ecu drivers failing.

If you have B+ going in, and a good ground, the ECU control should be no less than 4.2v (the closer to 5 the better) and should be a square wave.

My question to you is how are you testing? The signal control signal may very be 5V but if you’re testing with anything other than a scope or graphing meter, then you’re not going to know for sure. The meter will average out the signal over whatever spec time.