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Old 06-15-2018, 08:26 AM   #1
Weste46
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Default Wasted Spark Check

Hello,

I recently discovered through some reading that the distributed single ignition coil system on my EJ253 is a "wasted spark" system, meaning two cylinders spark but only one is actually in its TDC position.
Could I test my ignition coil by swapping wires from cylinder 1 and cylinder 2 on the ignition coil side? I'm getting a consistent cylinder 2 misfire at idle, and although I am fairly confident it is a compression issue, the last thing I can easily check would be the coil. Perhaps the distributor portion of the single coil pack is failing on cylinder 2 only (I don't know the inner workings of the ignition coil, so I can't say how it would fail).
Let me know if this sounds feasible. Thank you.
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Old 06-15-2018, 07:40 PM   #2
Elbert Bass
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No - 2 plugs, 2 wires and 1/2 a coil pack is one complete circuit. The only true diagnostic for waste spark systems is to inspect the plugs and coil towers (plugs for wear/coil towers for burns) and measure resistance of the plug wires and coils. Values vary between a couple different model years so I won't give you any values without a model/year.

I will say Subaru is VERY picky about that plug wire resistance. Aftermarket plugs wire are NEVER the correct resistance so ONLY replace with Subaru wires. Preferably a whole set (only about $65). Most aftermarket wires are too low in resistance and will burn out your coil(s)
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Old 06-15-2018, 08:37 PM   #3
Weste46
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Quote:
Originally Posted by Elbert Bass View Post
No - 2 plugs, 2 wires and 1/2 a coil pack is one complete circuit. The only true diagnostic for waste spark systems is to inspect the plugs and coil towers (plugs for wear/coil towers for burns) and measure resistance of the plug wires and coils. Values vary between a couple different model years so I won't give you any values without a model/year.

I will say Subaru is VERY picky about that plug wire resistance. Aftermarket plugs wire are NEVER the correct resistance so ONLY replace with Subaru wires. Preferably a whole set (only about $65). Most aftermarket wires are too low in resistance and will burn out your coil(s)
I'm not sure I follow. Why couldn't I simply change the orientation of the circuit, so that wire 1 is in the wire 2 position and vice versa?
It is a 2005 2.5RS.
I am using NGK wires, swapping wires from 1 to 2 didn't change anything, still missing on 2. I visually inspected the ignition coil on cylinder 2 and it looked okay, no corrosion.
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Old 06-16-2018, 07:45 AM   #4
Elbert Bass
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Swapping the wire from 1 to 2 doesn't change anything. If one wire is bad, then you still have a bad wire in the circuit. Where the ECU sees the misfire in waste spark is not necessarily which plug the bad wire is on, it is just the cylinder that is most susceptible to misfire. That is why you replace the set instead of just one wire.

If you understand electrical theory: The secondary circuit of the coil is wired between the two spark plugs - not each spark plug and ground as a coil-on-plug or old distributor systems. That is what makes both plugs fire at TDC compression/exhaust on the the companion cylinders.

Anyway, get out your ohmmeter and see if you have this:

#1 cord: 7,100 - 12,100 ***8486;
#2 cord: 12,100 - 19,900 ***8486;
#3 cord: 7,700 - 13,000 ***8486;
#4 cord: 12,300 - 20,200 ***8486;

coil 9,520 - 12,880 ***8486;

Look for burns/carbon on the coil towers, no corrosion/missing contacts in either end of plug wires. If it all measures out make sure you don't have a broken plug or bent electrode. Then start looking at mechanical issues - cylinder leakage, burnt valve, dropped valve guide...
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Old 06-19-2018, 04:07 PM   #5
Weste46
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I get what you're saying.
What I believe you are missing from my question is that I am wanting to troubleshoot the ignition coil/wasted spark system, not the plugs or wires. Those have only 20k miles, and I don't believe they are the issue (though I could be wrong, and will replace plugs soon to be sure).

Which cylinders spark simultaneously? I believe 1&2, then 3&4 fire correct?

I want to leave the wires on the same plugs and swap the wires at the ignition coil, so that I can have cylinder 1's ignition side spark for cylinder 2, in case it is an issue with the ignition coil.
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Old 06-21-2018, 07:41 AM   #6
Elbert Bass
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Yes 1 & 2 are on one coil and 3 & 4 are on the other.

What you are wanting to do with the wires won't tell you anything - the secondary side (spark) of the ignition coil is not center tapped or connected anywhere except to the spark plugs. The ignition pulse is generated in the coil by induction and the complete secondary circuit path is from the engine block through 1 spark plug - one wire - ignition coil - other plug wire - other spark plug - back to the block. The ONLY diagnosis for the secondary circuit (spark side) is to search for shorts, opens, or high/low resistance in that circuit. Reversing the direction of the coil in the circuit won't tell you crap and is a PIA.
Here's a diagram - plug numbers are wrong but the circuit is correct:
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Old 06-21-2018, 08:55 AM   #7
Weste46
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Ahhh, I finally understand. There are not two circuits going on in the wasted spark, but rather one circuit that includes both plugs and wires. In this case, I may just swap the ignition coil. As a matter of fact I have a buddy with the same engine, maybe I can swap with his to see if mine is defective.

Thank you!
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Old 06-21-2018, 08:57 AM   #8
Weste46
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Actually now that I think about it, if this was the case I still think my test might help... The intermittent connection would move to the other side of the circuit, right?

I'm going to chat with my dad on this, he is the electrical engineer...
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Old 06-21-2018, 08:00 PM   #9
Elbert Bass
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Swap coils and see if that changes anything. If you still have a misfire then show Dad the diagram and my electrical information in post 4. He can help you understand and make those measurements. Double check you haven't cracked a plug insulator. If that checks out then you need to look for the mechanical problems I have mentioned.
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Old 06-22-2018, 09:19 AM   #10
Charlie-III
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Quote:
Originally Posted by Weste46 View Post
Actually now that I think about it, if this was the case I still think my test might help... The intermittent connection would move to the other side of the circuit, right?

I'm going to chat with my dad on this, he is the electrical engineer...
Hate to say it, but if EB was correct on how it works, then you should get misfires off both cylinders on that coil if you had a bad plug, wire, etc.

The secondary coil builds a charge when the primary coil is fired, then the secondary charge just wants to go to ground.
Since you have 2 plugs, the charge will go through either one or both.
If you disconnected a plug wire at the coil, then ran the car, I would bet that you only get one misfire code, not two.
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Old 06-22-2018, 09:23 AM   #11
Weste46
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Quote:
Originally Posted by Charlie-III View Post
Hate to say it, but if EB was correct on how it works, then you should get misfires off both cylinders on that coil if you had a bad plug, wire, etc.

The secondary coil builds a charge when the primary coil is fired, then the secondary charge just wants to go to ground.
Since you have 2 plugs, the charge will go through either one or both.
If you disconnected a plug wire at the coil, then ran the car, I would bet that you only get one misfire code, not two.
Gotcha, it would misfire on either one not one specifically. Hopefully I'll see my Forester buddy and swap around parts one day to try to correct it.
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Old 06-23-2018, 04:30 PM   #12
Weste46
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Wire 4: 470 ohms
Wire 2: 450 ohms
Wire 1: 275 ohms

Plugs 1 and 2 didn't look that bad.

Then I went to check compression.
Cylinder 1: 145psi.
Cylinder 2: 50psi. Checked it twice.

So there we go. It's a compression issue. I'll have to pull it and see if it's valves or piston ring/ringland. Or I'll just get a used engine, who knows.
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Old 06-23-2018, 04:30 PM   #13
Weste46
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Also no idea why my wires were SO much lower resistance, but that's what I got.
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Old 06-23-2018, 04:40 PM   #14
Weste46
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Also could be a valve that was adjusted too tight, I didn't check them before the heads went on. Had a shop do the adjustments. That would mean the clearance has gotten tighter over time though.
I will likely pressurize cylinder 2 and listen for where it leaks, like people do during a leak down test.
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Old 06-23-2018, 05:12 PM   #15
Charlie-III
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Quote:
Originally Posted by Weste46 View Post
Also no idea why my wires were SO much lower resistance, but that's what I got.
Stock or aftermarket wires?
Usually over time, the resistance goes up until misfire.

Quote:
Originally Posted by Weste46 View Post
Also could be a valve that was adjusted too tight, I didn't check them before the heads went on. Had a shop do the adjustments. That would mean the clearance has gotten tighter over time though.
I will likely pressurize cylinder 2 and listen for where it leaks, like people do during a leak down test.
Could also be a valve seat that regressed into the head which yields a tight cam/valve clearance.
Yes, a leakdown test would show that and give an idea where to look.
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Old 06-23-2018, 06:39 PM   #16
Weste46
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Quote:
Originally Posted by Charlie-III View Post
Stock or aftermarket wires?
Usually over time, the resistance goes up until misfire.



Could also be a valve seat that regressed into the head which yields a tight cam/valve clearance.
Yes, a leakdown test would show that and give an idea where to look.
NGK wires, 20k miles.
Put new plugs in just for fun, 0.040 gap NGK iridium's.
Will report back with leak down test results!
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