troubleshooting no spark on one bank

[FFRWRX]

As I've posted before, I bought my 818C partially assembled. Apparently it was running fairly well when I bought it (I saw a video of it running), but after I took delivery it doesn't start or run well at all. I've been digging into it and found no spark on the 2 right side cylinders. I swapped coil packs around and they all work fine. There is 12V on each coil wire (the red wire). There are 2 other wires to each coil and I'm not sure what they are; even looking at a wiring diagram I'm not sure. The red lead is common to all the coils, and another lead is also common (ground?). Then there is one that must be a trigger connection to the ECU.

Does anyone know what the other leads should have in the way of voltage? Also, here is a picture taken from the left side looking across the engine. The coil leads from the right side go into a large harness that disappears under the intake; I'm pointing at it with the white pointer. Is there a connection somewhere I can check?

I wasn't getting any error codes indicating anything like this.

thank you,

Rick

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[Bob_n_Cincy]

As I've posted before, I bought my 818C partially assembled. Apparently it was running fairly well when I bought it (I saw a video of it running), but after I took delivery it doesn't start or run well at all. I've been digging into it and found no spark on the 2 right side cylinders. I swapped coil packs around and they all work fine. There is 12V on each coil wire (the red wire). There are 2 other wires to each coil and I'm not sure what they are; even looking at a wiring diagram I'm not sure. The red lead is common to all the coils, and another lead is also common (ground?). Then there is one that must be a trigger connection to the ECU.

Does anyone know what the other leads should have in the way of voltage? Also, here is a picture taken from the left side looking across the engine. The coil leads from the right side go into a large harness that disappears under the intake; I'm pointing at it with the white pointer. Is there a connection somewhere I can check?

I wasn't getting any error codes indicating anything like this.

thank you,

Rick

Hey Rick, Here is a picture of the schematic of my car. coils.jpg
On the right side of the picture it shows 2 ground blocks that bolt to the intake manifold. The ground wire from coil #2 and #4 go to the block on the right. I suspect a broken ground wire or a loose bolt in the ground block. I personally would run a heavy ground wire from the battery negative to the engine block. Do not trust running important grounds through ground straps.
Bob

[FFRWRX]

Thanks Bob.

The schematic I have is a bit strange. It has those blocks on it, but I didn't know what they were. Also, they seem to tie into the "ECM" and not the coils. Mine is a 2006, but I don't know if the schematic is from that; it came with the car. I'll do some hunting around for grounds that don't look like they are doing a proper job and maybe run a booster cable as a temporary good ground.

Rick

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[Ajzride]

So the problem doesn't swap sides even when you swap the coils? Have you tried swapping the plug wires around, I hear they are prone to going bad on Subarus.

[FFRWRX]

I tried each coil on a left side connection and got a spark from each one. Tried the same coils on the right side, front and back, and no spark. Not sure what you mean by plug wires. There is a connector on each coil, but the wires from those connectors disappear into large harnesses, so I don’t think they can be removed. Heading out to do some more poking around.

[FFRWRX]

It starts and runs! What I did from the start:

Car would start and run when I got it, but very poorly and only when floored to start it and then holding some throttle to keep it running. There were a bunch of codes for secondary air system (which would not have anything to do with this). There was a code now and then for the throttle position, but not consistent.

I did the usual checks: fuel pressure, connections all correct, no throttle body blockage, good battery voltage...no help. Didn't sound or feel like it was running on all cylinders.

So some time off to clean the garage before I got serious with it.

Checked the plugs: very sooty and very large gap. I left them soaking in brake cleaner while I checked for spark. Here is where I missed something.

I rigged up this gizmo so I could check for spark while cranking the engine from the drivers seat. One wire goes in the coil plug and another goes to ground. They are insulated from each other, but close together to throw a spark (blue circle in picture). Showed me sparks on the left bank but nothing on the right. Swapped coils around....no difference. Removed and cleaned the 2 major grounds from the intake manifold and removed and cleaned the ECU connections. No difference. Ran a temporary ground (booster cable) from the battery to the intake ground point. No difference. Had me stumped at this point.

Then my wife made the mistake of coming out to see what I was up to. I closed the garage door to make it a little darker and told her to look for a spark (with my spark testing gizmo in place) anywhere on the right side. Right away she said there was spark. It was where the red circle is in the picture. It was sparking from one of my wires to a rubber hose. I deliberately rested the tester on the rubber hoses so it wouldn't spark where I couldn't see it from the drivers seat. I moved the tester so it wasn't against anything, and got a spark at the end of it where I was expecting it. Success!

I did check the plugs and they were gapped to at least .045". I reset them to around .031". Put it back together and it fired right up and ran well. Beautiful!

So what was the original issue? Maybe the plugs were gapped way too big and the spark couldn't consistently bridge it? Combine that with maybe dirty grounds (though they didn't look too bad). Oh, when I was testing the spark after getting the tester position sorted out, I did notice a bit of a change in the spark when I removed the temporary booster cable ground, so obviously that was helping things.

While it does idle fairly well and rev lightly well, it does not want to rev above about 3500 RPM. I think there may still be an issue with the throttle position sensor system. The car came with a bunch of sheets from a service manual on trouble-shooting that system, so maybe there was an issue and may not have been sorted out. But now that it is running it will be easier to do.

Thank you for the suggestions and the wonderful support!

Rick

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[aquillen]

Looks like you are past the issue, but to clarify what the wires into the coils are:

> 12V power to each coil
> Ground (from engine-ECM ground blocks) - this is a main common ground "group" for the ECM and a lot of stuff it controls/reads so that it doesn't have a bunch of different grounds.
> Individual spark commands to each coil from ECM

Not only the ground but the 12V must be good to each coil. A poor connection in either would reduce or prevent spark when the ECM signal to a coil occurs. Of course all three have to be good or you'll get weak (poor connection) or no (lost connection) spark.

Could be wrong but I really doubt a .045 gap would prevent spark unless something coil is going bad or 12V/Ground is not 100% solid.

[Bob_n_Cincy]

Interesting: plugs.jpg
I thought the coils were the same between NA and turbo. I wonder why the difference in gap.

You said that the spark changed when you took off the jumper cable.
If that is true, you have a bad ground connection between the battery and engine block. this is the spark tester I use.

gap.jpg

you can adjust the gap to see how big you can get.
I usually see 3/8" ti 1/2" with electronic ignition. About 10 time what you need.
BE CAREFUL, TOUCH THIS DEVICE WHILE ENGINE IGNITION IS ON, CAN HURT OR POSSIBLE KILL YOU WHEN THE COIL FIRES

[FFRWRX]

That's a cool spark tester. Edd on Wheeler Dealer made something like that once to see how big a spark he was getting before and after some mod. Mine was a quickly rigged up thing, but I wanted to see it while in the drivers seat cranking the engine. Turned out it lead me in the wrong direction for a while.

Maybe the turbo engine, when under boost, makes it harder to throw a spark with a larger gap?

I'm going to check my ground path from the battery to the intake grounds and maybe add an additional one. When I removed the booster cable ground, even my wife said that it looked like the color of the spark changed.