2009 Forester Cylinders 1, 2 misfire coil problems

[q240z]

Hi.

Two years ago I had a misfire problem with my '09 Forester. The code reader indicated cylinders 1 and 2 were misfiring. I popped the hood at night just by coincidence and saw sparks around the #2 plug wire connector. When I pulled the wire, it was clear that water had gotten in, corrosion started at the coil connection to the wire, and the coil tower had melted. I swapped out the coil, wires, and plugs and it ran fine for a while. But the missus started complaining about sporadic poor performance recently, and the car started throwing the same misfire codes again. The replacement coil (Ultra Power) looked fine, but when I put a multimeter on the primary side pins (read left side to right, facing the primary side plug), I get:

infinity between pin 2 and all of the other three pins

2.13 ohms between 1 and 3

4.28 ohms between pins 1 and 4

2.14 ohms between pins 3 and 4.

Online sources vary, but a common spec is that I should be seeing ~ 0.73 ohms between 1 and 2 and also between 3 and 4, or alternatively between 1 and 2 and 1 and 4.

Thoughts?

BTW, I didn't go with an OEM coil because the OEM one didn't last 100k miles and I figured a coil is a coil.

Thanks!

Q

Edited January 25, 2020 by q240z
clarification

[ocei77]

See following from FSM/

You can download FSM from here

http://jdmfsm.info/Auto/Japan/Subaru/

O.ignition coil and ignitor assembly.pdf

[GeneralDisorder]

Aftermarket coils are crap. Likely your problem. In fact a 1/2 misfire on a wasted spark ignition system is going to be a coil 99.99% of the time - since that's prettymuch the only thing shared by 1 and 2. Get an OEM coil. 100k is a good run for a coil. Also (OEM) coil failures are typically a result of plug gap being too large or the wires being shot. Anything the increases the secondary ignition voltage requirement will cause more heat in the coil and kill it sooner. 

GD

Edited January 27, 2020 by GeneralDisorder

[Rampage]

Measuring ohms on the connector pins of the coil is not going to tell you much about the coil. The newer coils have the Ignitor built into it at the input. When you are seeing is a transistor circuit that is affected by the voltage from your ohm meter.

All you can measure on the coil with an ohm meter are the output terminals. Around 11K between 1 and 2 and the same between 3 and 4.

[q240z]

Thanks for the responses.

The aftermarket coil doesn't appear to be the problem. The original coil problem was caused by thoroughly corroded coil wire to coil connection. The problem appears to be most likely in the wiring, based on the FSM ocei77 linked to.

It's funny. For all of the threads online complaining about this same problem (sporadic misfire),  none of the threads I've seen identify what the final solution was. Many go down the random parts replacement path, with claims of "Fixed it!" followed by "it came back" shortly thereafter. When I finally figure out what's causing this, I'll post it here.

[Rampage]

On 1/25/2020 at 5:30 PM, q240z said:

I swapped out the coil, wires, and plugs and it ran fine for a while.

Did you use NGK wires and plugs?

[q240z]

I don't recall, but the problem is intermittent so it's unlikely to be wires or plugs.

The car runs great, then out of the blue it feels like somebody turned cylinders 1 and 2 off. They come back on shortly thereafter (2~20 seconds). That doesn't strike me as a plug or wire issue. When it  happens, it temporarily throws a code for cat inefficiency. That tells me the injectors are firing fuel that's not getting lit off by the plugs, loading up the cat. I've already tested the injectors. They're working fine. All of the readings on the aftermarket coil are identical to a known good OEM coil.

[1 Lucky Texan]

can you install the original coil again as a test?

[heartless]

20 hours ago, q240z said:

I don't recall, but the problem is intermittent so it's unlikely to be wires or plugs.

The car runs great, then out of the blue it feels like somebody turned cylinders 1 and 2 off. They come back on shortly thereafter (2~20 seconds). That doesn't strike me as a plug or wire issue. When it  happens, it temporarily throws a code for cat inefficiency. That tells me the injectors are firing fuel that's not getting lit off by the plugs, loading up the cat. I've already tested the injectors. They're working fine. All of the readings on the aftermarket coil are identical to a known good OEM coil.

False.

Aftermarket wires are KNOWN to be problematic, causing all sorts of weird issues, most commonly random misfires.

Plugs should be NGK, wires should be OEM or NGK only. Any other brand is suspect

[idosubaru]

Aftermarket wires are often problematic, particularly low cost ones, I’ve seen them cause misfires right out of the box on EJ engines. I will use zero aftermarket parts for plugs wires and coils.

id install a used OEM coil before buying a new aftermarket.  

some people think aftermarket is fine, I know plenty of people like that. If that’s you then go through the FSM exactly step by step and see where it leads.

using the cat inefficiency code as a diagnostic tool is probably low efficacy. 

[GeneralDisorder]

Likley internal coil ignitor failure. Cheap electronics in the coil pack. Overheat and stop working.

You want to know for sure? Stick a scope on the ECM 1/2 coil driver signal, and the 1/2 secondary ignition. Drive till you get a failure and capture it. If you lose the driver signal you have wiring or ECM issues. If you don't you need a coil. 

GD

[q240z]

I don't have a scope, but I did put a timing light on the #1 wire and went for a drive. Some threads indicated injectors caused the problems I was seeing, and the timing light made it clear it was ignition cutting out. When the car would start to stumble, the timing light wouldn't flash. But even when the engine was running right, the flash seemed to vary quite a bit. I swapped out the aftermarket coil for a known good OEM one and the car drove much better for a while. But the idle still seemed weak.

I found another thread on teaching the ECM idle parameters (disconnect battery for 30 minutes, reconnect, turn key on, wait 20 seconds, start engine and let idle for 20 minutes). But the car wouldn't idle. It'd die after ~5 minutes.

I found another thread that discussed cleaning the throttle body. Something about the throttle blade not closing fully if there's gunk around it. So, I took off the TB and--sure enough--there was a lot of gunk inside. I cleaned it up with solvent and a soft brush, then wiped the blade face and edges and TB bore clean. I was then able to reset the ECM. It idled fine for 20 minutes. I shut it off for a minute. Then turned the ignition on without starting the engine for 20 seconds. Then started it and it ran well for five minutes. That's it. The ECM is now controlling the idle properly.

I would say, though, that it's pretty clear the problem with the TB wasn't that the blade couldn't close. It's that the gunk around the perimeter of the bore and edge of the blade blocks the very narrow gap between the blade and the bore. Unless I'm wrong, that gap passes just enough air that, without it, the idle becomes unstable.

Either way, it's looking good right now. Lesson learned on the non-OEM coil. The non-OEM plug wires and plugs don't appear to have been a factor.

If trouble comes back, I'll post again. Thanks for all of the suggestions.

[Rampage]

Glad to hear you fixed it. There are so many possibilities to work through for certain problems and it takes some research to do it.

So, I guess the ECM was seeing readings from the Throttle Position Sensor and air flow that were not what they should be.

[q240z]

Aaaaaaaaand I'm back to the same  PO301 PO302 codes. I put my inductive timing light on the plug wires again, and when the engine starts stumbling the timing light stops. Which means there's no juice going through the wires to cylinders 1 & 2. I have a new OEM coil, clean MAF. New cat and O2 sensors. Good plugs replaced less than 10k miles ago, and they're properly gapped.

I swapped the coil wires 1 to 3 and 2 to 4 and vice versa. No change, still throwing codes on cylinders 1 & 2, so the problem is not the plug wires.

And the problem has gone from being intermittent, once every couple of days or so, to almost constant.

Has anybody whose actually solved this misfire problem tracked down the real cause?

[ocei77]

Check your timing and that the sensors are clean, especially the crank.

O.

Edited April 27, 2020 by ocei77

[q240z]

Could you explain why you think that would cause the spark to cut out only on cylinders 1 & 2 , leaving 3 & 4 unaffected?

[ocei77]

If the timing is off they are not getting the correct signal at the proper time..

Easy to check by removing the timing cover and aligning the crank.

If the car is not underpowered, they are firing at some point.

Make sure you have continuity and correct resistance between the bulk harness and the injector terminals.

There  are diagnostics  and connector listings in the FSM, which you can download here:http://jdmfsm.info/Auto/Japan/Subaru/

Wiring would be under engine electrical

Are you only getting codes 301 and 302?

O.

[q240z]

I'm pretty sure that if the timing was off or the crank or cam position sensors weren't working right, the problem would affect all cylinders, not just 1 & 2. Also, it wouldn't be intermittent, it would be all the time. The symptoms don't fit that diagnosis.

The problem is not fuel related. As I said, my inductive timing light stops flashing on cylinders 1 & 2 when the engine starts to stumble (the dashboard warning lights start flashing at the same time). That means there's no spark coming from the coil, but only on cylinders 1 & 2.

As to codes, 301 and 301 are the primary ones, but I also get the one indicating cat efficiency is off. But that's to be expected with a misfire on two cylinders and injectors still spraying fuel. It's more of a sub-symptom than a primary one.

[ocei77]

Perplexing. 

Although the coil and plug wires are new, try anyway to see if you are getting leakage at the terminal.

At night or in a dark garage, let vehicle run and when it stumbles, spray water with a mister around the connections.

Check voltage at coil when it stumbles, one plug at a time and be careful!

Again, check your sensors won't take but a few minutes. The ignition signals go from the sensors to the ecu and then back to plugs.

Get FSM and go to the 300 series of DTC's there are 4 pages of troubleshooting

O.

 

[1 Lucky Texan]

1 & 2 of course share a coil due to waste spark ignition.

 

checking alignment is not hard, align the crank and do a tooth count. if it sometimes starts/runs, it can't be more than a coupla teeth off. longshot but cheap and easy.

 

no signs of oil on the wire boots? no association with dew/moisture?

[q240z]

The problem is intermittent, so it can't be timing. There's no oil or moisture on the boots. Plus, the inductive timing light is showing that no juice is getting to the plug wires. There's no evidence of leaking voltage either.

It's good to know 1& 2 share a coil. Looking closer at the design, I can see that now. But what are the odds of an OEM replacement coil having the same problem as the one it replaced?

The FSM wiring diagram is helpful but also confusing. It shows terminals on the coil ordered 3214, but on plug E12 they're ordered 1234. Once the rain stops here, I'll pop the hood and try to figure out which is correct through a process of elimination.

Also, any idea where the ECM is and how to get to it?

[ocei77]

The diagram just is just telling you what colors the lead wires are. You missed the optional arrangement note.

ECU is under carpet in passenger footwell.

O.

[q240z]

Thx on the ECU location.

The jpg I posted was only a partial on the wiring diagram. The "*1" optional arrangement refers to connector B-122,  which is further up in the diagram, not the pin order on the coil. The order of the pins should be consistent unless there's some note on the diagram explaining why they're not.

 

[Rampage]

You have changed the coil and it is still dropping spark on 1 and 2 so check the inputs to the coil and where they come from.
Uncover the ECM and identify the two wires and pins 18 and 19 on connector B137 so you are ready to test them. With the key off, remove connector B137 from the ECM and look for corrosion on pins 18 and 19. I have not seen corrosion on those pins, but anything is possible. Replace the connector.
Use a volt meter and compare the voltage on Pins 1 and 4 of the coil plug (the two outside pins) when the engine is running normal and again when it is misfiring. When misfiring, there will be a difference in voltage on one of those pins.
When it is misfiring check the voltage at the ECM connector B137 Pins 18 and 19.
If the voltages on the ECM pins read the same as on the coil, then the ECM is at fault. If they are different then the problem is the wire between the two connectors.
I don't know if the difference in voltage will be a high or low, since I don't know if they use NPN or PNP transistors in the coil and ECM.

 

Edited May 1, 2020 by Rampage

[heartless]

the lower connector drawings are the correct pin orientations...

the wiring diagram connectors are laid out only for ease of drawing them.. do NOT use them for pin orientation.

Edited May 2, 2020 by heartless
can't spell, lol