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WTF??? (resistance specs for '02 OBW 2.5 coil?)


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#1 skizix

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Posted 04 July 2006 - 01:45 PM

Anybody have the reistance numbers for an '02 2.5 OBW (105,000 miles) coil pack?

I tested mine, and got 13.73k-ohms across the plug wire terminals. Front and back were within 0.03k-ohms of each other, which I assume is a good sign.

For the primary, I got 1.42 ohms across the two rear-most pins. All other combinations of pins had infinite resistance.

THIS ARTICLE quotes the numbers for a 2.5 liter as:

secondary: between 10k and 24k ohms
primary: 0.40 to 1.00 ohms

So, looks ok for the secondary (but is it good or bad to be at the low end?), but my primary appears to be out of range. Can anyone confirm if my coil is out of range? What does it mean if the primary is out of spec? Fried igniter?

Also: if it IS within spec, does this mean my coil is necessarily good? I am having some bucking issues at low speeds only (e.g. parking lots, slow-and-go traffic, etc.) and sporadic misfires (no codes stored). The coil does not appear to have any cracks. New wires and plugs.

Any other way to test the coil? I saw this blurb in an ebay ad for this same coil pack (used -- no thanks): "THESE COILS HAVE A HABIT OF ARCING THROUGH THE TOWERS ONCE THEY GET OLD, IF YOUR CAR IS BUCKING...TRY THIS."

I'd hate to drop $100 for no effect, but I sure would like to resolve my driveability issues, and coil pack is my best guess at the moment. In a minute, I'm going to try some dielectric grease on the coil terminals? Anybody else use that?

#2 OB99W

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Posted 04 July 2006 - 06:20 PM

Anybody have the reistance numbers for an '02 2.5 OBW (105,000 miles) coil pack?

I tested mine, and got 13.73k-ohms across the plug wire terminals. Front and back were within 0.03k-ohms of each other, which I assume is a good sign.

For the primary, I got 1.42 ohms across the two rear-most pins. All other combinations of pins had infinite resistance.

My own '99 OBW has a separate ignitor and dual-coil, with a 3-pin connector at the coil. I believe the '02 has the ignitor and coil(s) as one assembly; if so, you can't easily take coil primary readings.

The secondary resistance readings you got seem about right, but unfortunately resistance checks don't show up problems that occur under high voltage, and some other types of failures. In addition to resistance across each secondary coil, Subaru usually suggests checking for leakage from secondary coils to ground; anything lower than 10M-ohms is considered a problem. However, if you see any conduction from a secondary to ground at the low voltage that an ohmmeter typically applies, at spark voltage it will be a lot more significant.


THIS ARTICLE quotes the numbers for a 2.5 liter as:

secondary: between 10k and 24k ohms
primary: 0.40 to 1.00 ohms

So, looks ok for the secondary (but is it good or bad to be at the low end?), but my primary appears to be out of range. Can anyone confirm if my coil is out of range? What does it mean if the primary is out of spec? Fried igniter?

That article may have been written before the combined ignitor/coil-pack was used. I don't have resistance data on the '02, but in most cases resistance tests of solid-state device inputs or outputs won't easily reveal subtle problems, which is what you seem to be describing.


Also: if it IS within spec, does this mean my coil is necessarily good? I am having some bucking issues at low speeds only (e.g. parking lots, slow-and-go traffic, etc.) and sporadic misfires (no codes stored). The coil does not appear to have any cracks. New wires and plugs.

Resistance testing of the coil often doesn't reveal certain problems. So no, in-spec resistance readings don't guarantee a problem-free coil.


Any other way to test the coil? I saw this blurb in an ebay ad for this same coil pack (used -- no thanks): "THESE COILS HAVE A HABIT OF ARCING THROUGH THE TOWERS ONCE THEY GET OLD, IF YOUR CAR IS BUCKING...TRY THIS."

I'd hate to drop $100 for no effect, but I sure would like to resolve my driveability issues, and coil pack is my best guess at the moment. In a minute, I'm going to try some dielectric grease on the coil terminals? Anybody else use that?

There are some devices for testing high-voltage components, and an ignition scope might show up a problem. However, diagnostic charges would probably exceed the cost of a new coil pack. Sometimes you can spray down the coil (or plug wires, etc.) with a water mist when it's sufficiently dark, and see leakage as sparks; however, if it's occuring within the coil, this won't reveal it.

It could be worth the gamble to try a new pack, assuming you're fairly convinced the problem is an ignition issue.

#3 skizix

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Posted 04 July 2006 - 06:55 PM

Thanks for the input. Subtle problem...yes. The car drives great, for the most part, but low speed manuevering is kinda crappy. When I let up on the accelerator pedal, rpm in the 2000's, 1st or 2nd gear, the transition fron acceleration to coasting is very abrupt, when I hit it again...very abrupt. I don't think it's just the way this car is, because sometimes it is quite smooth, as one would expect (sometimes I can compensate by focusing on very subtle adjustments with my foot, sometimes it will do it no matter how careful I am, sometimes it is fine no matter what). My '90, with 235,000m, which I just sold, was butter-smooth every time, and so is every other car I've ever driven (relative to this car, anyway), including my friend's 2000 OBW. It is not a huge problem, but passengers are consistently like, "whoa, what the hell was that!?". Not devastating, but annoying as hell.

The other symptom is: when I go to upshift (5MT) and disengage the clutch, the rpm's drop really fast. Like, I have to really quick-shift to match revs -- 4th to 5th is tough (not like that is a big deal, but it's a sign, I think). Also, I've had infrequent, sporadic, what feels like misfires. Seemingly random, I've had it happen at low speeds, like I described...engine just bottomed out when I went to accellerate out of a turn. Recently I had bomb out right on startup (started the car, bombed out to where I thought it would stall, then recovered, all in ~1.5 sec. -- not coinciding with an ECU reset, which seems to do that anyway). No codes.

At high speeds, I have no real problems, other than the too-quick loss of revs on clutch pedal depress. A couple of times I've had it blip at speed, like a misfire, but momentum, I guess, made that not a big deal. Highway driving is basically smooth and fine.

Dielectric grease seems like it has helped a little. Maybe (it is so hard to separate psychology from these intermittent problems). Seems to start after fewer cranks. It is still "abrupt" at low speeds. Most of the time, anyway.

So, does this still sound like coil to you? I'm thinking of pulling the trigger. The only thing that makes me think it might NOT be coil is: problems are lesser to non-existent at speed. Low speed off-and-on the accel-pedal kinda sucks. I thought coil issues should be WORSE at speed, not better.

So...think I should buy a new coil? Any other suggestions?

#4 OB99W

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Posted 05 July 2006 - 08:35 AM

I was going to ask a bunch of questions, but found your previous thread http://www.ultimates...ead.php?t=59375 .

I'm not inclined to think that the coil is causing your problems, although stranger things have happened. Due to the intermittent nature of the symptoms, it would be good to get some real-time data from sensors. That might be obtained with an OBD-II scan tool (not a "code reader" which only retrieves stored codes). Obviously, it would require an observer other than the driver, or a scanner that can record the output for a while (laptop computer running OBD-II software?).

Any possibility that some of the symptoms are clutch-related? It would almost seem that the clutch not properly engaging/disengaging could cause part of what you've described.

I've got another idea, but before I stick my neck out and have my head chopped off ( :) ), I've got a question; does the engine rev freely and reach high RPMs in each gear without problem consistently (other than what you've already described)?

#5 skizix

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Posted 05 July 2006 - 10:53 AM

Well, don't get me started on the clutch. I've got the judder -- not too violent, but it lasts ~20 min. into my commute, even on the hottest, driest day. Then it's solid, with zero slippage, engages smoothly. Pretty much accepted that that's going to be like that 'till I get a new clutch. Not my first sube, so I'm used to it, but it's sad that it went on for so many model years.

ANYWAY AND HOWEVER...that has nothing to do with what I'm describing here. The abrupt transition from acceleration to coasting I'm talking about is all with the clutch fully engaged -- not touching the pedal. Simply talking about cruising along at low speed in 2nd, then letting up on the pedal to decellerate...LURCH, the car "grabs" and slows down abruptly and jerks all passengers forward. Then when I go to give it some gas to speed up...LURCH, the car jerks forward. If this coincides with, say, a speed bump, it can set off a series of bucks, car bouncing all over the place. Occasionally the engine will momentarily drop out, as well, as if it has misfired.

The kicker is: it does not happen all the time. Sometimes it is smooth as silk; sometimes it is moderately jerky; sometimes it is really obnoxious. And when it is bad, it is bad for a while, like it is going into a particular "mode". I cannot correlate it with any particular driving/climate conditions however -- seems random.

As for my previous thread that you linked to...keep in mind that I've resolved some of those issues. A new O2 sensor and the ECU reflash (which I believe is designed to dampen the ECU's response to the O2 sensor) have fixed my hesitation issues pretty well.

In addition to those two things, I've also done: plugs, wires, air/fuel/oil filter, cleaned IAC. Everything has helped, but I've still got the jerkiness at low speeds.

Yesterday I polished the coil secondary terminals with 600 grit, exposing fresh brass, splooged some dielectric grease on 'em, and reconnected. I've still got the jerks, but they seem less frequent. More smooth transitions than I've seen. The question is: is the improvement real, or placebo effect (i.e. my optimistic perception)? Kinda makes sense that if the coil were arcing internally, decreasing the resistance of the correct spark path would decrease the likelihood of the wrong path (internal arc).

But of course, I'd rather not blow $100 if I can help it. I am open to any and all suggestions/theories/opinions (but like I said...not a clutch thing). Fire away!

#6 skizix

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Posted 05 July 2006 - 03:11 PM

Forgot to address this:

I've got another idea, but before I stick my neck out and have my head chopped off ( :) ), I've got a question; does the engine rev freely and reach high RPMs in each gear without problem consistently (other than what you've already described)?



Yes. Revs freely and reaches high rpm in each gear consistently.

As noted above, however...it un-revs a bit TOO freely (when I disengage the clutch, the revs drop very quickly). Maybe that's how it's supposed to be (it's not intermittent), but it's way faster than I'm used to from my '90 Legacy, or other cars.

So...hoping you will choose to stick your neck out...

#7 OB99W

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Posted 05 July 2006 - 07:14 PM

Sorry, there's no reason for me to risk injury ;) ; the engine's ability to properly reach high-RPM operation eliminates what I was considering. You may be experiencing normal engine braking. My '99 has a 4EAT, and I've always felt that it slowed faster than I thought it should when I lift my foot off the accelerator. I attributed that to friction, etc., in parts of the drivetrain other than the engine, but maybe that's not the case.

Hopefully someone else will have a suggestion, or you can compare notes on how fast the revs drop when off-throttle in other's cars.

#8 skizix

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Posted 05 July 2006 - 09:23 PM

Well, today I tried to pay very close attention to things, and was deliberately speeding up and slowing down repeatedly at parking lot speeds -- must've looked like an idiot.

Anyway, I gotta think something is not as it should be, as there is such a big difference in when it transitions smoothly, and when it does not. And when it's at it's worst...it's pretty bad (btw, I'm talking about being very smooth with the pedal -- yes, a little jerk if you mash the pedal or let up suddenly from floored seems normal)

As far as the rpm's dropping too fast: checking it out, it seems as if what it does when it's good is not so much fall slower, but pause for a sec after disengaging the clutch before rpms start falling, vs. dropping immediately. This would seem to jibe with the jerky transition to engine braking.

The other symptom I still have is: when I'm cruising along, and let up on the pedal 'till it's just on the cusp of engine braking/acceleration and hold it there, there is a slight push-pull from the engine, as if I'm up and down with my foot, no matter how steady I keep the pedal, and I can see the tach go up and down a little. Also intermittent. Not really a problem, but it does not seem right.

Honestly, it does seem somewhat better after greasing the coil terminals. Less modal (more random) and less obnoxious more of the time. Seriously considering ordering up a coil.

Anybody got other ideas/theories about this? Still think it is definitely NOT the coil? Thanks folks.

#9 OB99W

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Posted 06 July 2006 - 07:21 AM

Surging, unfortunately, can be due to lots of things, including ignition problems (so do consider the coil for that aspect). A sometimes simple problem can be vacuum leak(s). Another possibility is an O2 sensor not performing well -- I know it's been replaced; was that with an OEM (or equivalent) unit? Other sensors might be acting up. If the '02 has an EGR valve, it could be (intermittently) sticking.

The "problem" with modern engine management systems is that the feedback from the sensors and the constant "adjusting/correcting" leads to difficulty in pinpointing the actual culprit. I still think your situation could benefit from an OBD-II real-time sensor scan.

By the way, apparently owners of '06 Foresters with MT have complained about surge problems. Perhaps you can find out if there's a standard approach to resolving that.

#10 skizix

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Posted 12 July 2006 - 08:03 AM

Ok, WTF???

I finally got my factory service manual cd in the mail, which lists the resistance specs. I removed the coil to measure, as indicated. Seconday resistance spec is 12.8k ohms +/-15%. I got 14.1k ohms both sides, so that looks to be good.

It also gives directions to check primary resistance. The connector has four pins, numbered 1-4 from front to the back. It says I should have 0.72 ohms +/-10% between pins 1 and 2, and the smae between pins 2 and 4.

Here's the F'd up part: I got infinite resistance between 1 and 2, infinite resistance between 2 and 4, around 1M ohm between 1 and 3, and around 1M ohm between 2 and 3. I have no idea what to make of this. Does this mean I have a problem??? Not exactly the way I'd expect a problem to show itself, at least on a coil that does make the car run, mostly normally. What is going on here?!?

Also: this engine (2002 2.5 liter, 5MT) apparently does not have an EGR valve, so that is not an issue.

Two other weird things: 1) the IAC I have is the one they show for the auto tranny model (I have the one that mounts on the side of the throttle body, with no coolant line going to it; the 5MT is supposed to have the top-mount one, with coolant going to it -- the coolant line is supposed to be sensed for cold engine idle). 2) I have an injector air assist valve, which according to the manual is only supposed to be present on the auto-tranny model.

What's up there? The manual is for both 2001 and 2002 outback/legacy, so maybe things changed a little for 2002, but it seems odd to me.

I get the basic idea behind the injector air assist valve, but I have no idea when it would open or close, or what symptoms it might precipitate if not working properly. Anybody know how that thing operates? Could that be causing my drivability issues?

Also: two of the three bolts securing the coil had significant corrosion, and one of the bolt holes in the coil had some of it's shiny plating chipped off. Are those signs of a coil in trouble? I wire brushed the bolts clean, and reinstalled with anti-seize on threads, and dielectric grease where bolts contact coil -- didn't seem to make any difference in driving.

So, who thinks i have a bad coil? Good coil? Do you think cleaning my injector air assist valve could help?

thanks.

#11 Cougar

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Posted 12 July 2006 - 10:17 AM

Frankly, I don't think the trouble is caused by the coil. It is curious though why the primary resistances are showing the readings you gave. It sounds like you got the pin numbers right according to the manual. Pin 1 is on the right side as you are looking at the pins. If you have a salvage yard close by perhaps they may have a coil you can compare readings with.

#12 skizix

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Posted 12 July 2006 - 11:06 AM

The fact that greasing the secondary terminals seemed to help was continuing to make me think coil. But since issues are intermittent, it's tough to be certain that it actualy did anything.

What else would you suspect? I was thinking maybe vacuum leak. Is there a trick to finding these? I'm not seeing any damaged lines.

And thinking vacuum leak, but intermittent, I got to thinking: sticking valve (not engine valve, but a air bypass valve or whatnot). IAC was looking quite clean when I pulled it, but I cleaned it anyway. I have no EGR valve. This is why I brought up the injector air assist valve. Think that could be it? What other valves are there to stick?

Any other ideas for this intermittent problem? When dealer reflashed my ECU, they thought a top-end cleaning might help. Seems like the dealer is always trying to sell that though.

#13 OB99W

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Posted 12 July 2006 - 01:15 PM

It also gives directions to check primary resistance. The connector has four pins, numbered 1-4 from front to the back. It says I should have 0.72 ohms +/-10% between pins 1 and 2, and the smae between pins 2 and 4.

Here's the F'd up part: I got infinite resistance between 1 and 2, infinite resistance between 2 and 4, around 1M ohm between 1 and 3, and around 1M ohm between 2 and 3. I have no idea what to make of this. Does this mean I have a problem??? Not exactly the way I'd expect a problem to show itself, at least on a coil that does make the car run, mostly normally. What is going on here?!?

It appears that the manual may have incorrect info for the coil pack that has an integrated igniter.

As far as I know, the MY99 Legacy/OBW was the last to have a separate igniter (mounted to the firewall, fairly high and near center) and coil pack. On the '99, the connector at the coil is a 3-pin, and those pins connect to the two coil primary windings (one pin is common to both primaries). On these units you'll see low resistance readings (about 0.7 ohms per primary coil).

From MY00 on, the igniter and coil are apparently integrated. The info I have available shows the 4-pin connector includes ground, power, and two pins going to the built-in igniter (coming from the ECU). That would mean that the coil primary connections aren't available at the 4-pin connector at all, and the high resistance readings are likely those of semiconductor circuitry that isn't being turned on by the low voltage typically provided by an ohmmeter. The high readings are probably normal, especially since (as you mention) the engine basically runs. It's possible that you might see some different resistance readings if you reverse the ohmmeter lead polarity, and/or if your meter has a "diode test" position. (Not that I think those readings would be very revealing, anyway.)

If you haven't already done so, checking resistance from the coil secondary terminals to ground might be useful. If you see any conduction there (Subaru says under 10 Mohm is a problem, but I say even considerably higher than that is a bad sign), the coil has leakage. To verify that you should expect those readings to be quite high, I just checked my own coil secondaries to engine ground with a meter capable of reading resistance up to about 1,000 Mohms, and it reads infinite. A similar reading should be found between secondary terminals of one coil and the other in the pack.

As I've said before, problems that an ohmmeter shows up shouldn't be ignored, but "correct" ohmmeter readings of a coil aren't sufficient to clear it; and ignition is only one possible cause of surging.




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