Coil measurements 1999 OBW

[von.ah]

Yes, the head gasket was replaced. After a melt down.

I'm having ignition problems and keep getting a P0303 code. I measured the #3 wire resistance, and it seems OK. On the coil (with the igniter disconnected), I measure 14 kOhms for 1-2 and 3-4, but get overload readings for the 2-3 (and 1-4) measurement. I realize this may be a dumb question, but do I need a new coil? I know it should be ~ 0.7 Ohms, so "infinite" resistance means it's not doing well, right? Or am I doing something wrong with the measurement?

Thanks so much for any help.

[nipper]

infinite resistance is the same as holding one probe in your left hand, the other in the right, and spreading your arms apart.

 

That being said, the subaru ignigiton system sues a waste spark system. this means that 1-2 and 3-4 fir together, and are two totally independent coils. 2-3 and 1-4 should not be electrially joined, so this is a proper reading.

 

NOw your code...

# 3 misfire is a fairly common code. It means that either the coil is failing, the wires are tired, or there is a hairline crack in the coil tower.

When was the last time the car had a new set of ignition cables?

Move the #3 wire to the #1 position and see if the code follows. if it does its the ignition cable. If it doesnt its most likely the coil is at fault.

In the past after we tell people this, we never hear from them. This means one of three things. A new coil fixes the problem, the car exploded into a million peices incinerating them, or that somehow they made a hole in the space/time fabric of the universe and got sucked in.

 

So how is your physics?

 

hehehehe

 

 

nipper

[OB99W]

[...]On the coil (with the igniter disconnected), I measure 14 kOhms for 1-2 and 3-4, but get overload readings for the 2-3 (and 1-4) measurement. I realize this may be a dumb question, but do I need a new coil? I know it should be ~ 0.7 Ohms, so "infinite" resistance means it's not doing well, right? Or am I doing something wrong with the measurement?[...]

There have been several errors in the End Wrench articles concerning measuring coil pack resistance; if that's your point of reference, it's no wonder you're unsure what's correct.

 

The 14 Kohms reading for the secondaries seems about right; my own '99 OB measures slightly below 13 Kohms for each coil. The ~0.7 ohm reading is what you should measure for each primary; that is, primary terminal 1-2 and 2-3 (therefore ~1.4 ohms for 1-3).

 

In addition, you should check from each of the secondaries to both ground and the primaries. The resistance should be extremely high; I'd expect most DVMs to indicate "overload", i.e. infinite resistance.

 

Of course, resistance checks won't detect subtle problems in the coils.

 

You could check for any corrosion at the ends of the secondary wires, the coil terminals, or the plugs, and that the connections are tight. It isn't unknown for either to cause some misfire, especially at idle when the engine is cold.

 

Some misfires are caused by secondary voltage leakage. You can check for that by starting the engine and opening the hood at night; stray sparks should be more obvious that way. Water from a bottle lightly sprayed on the coil and secondary wires can also help in finding underhood high voltage leaks, since a "tight" ignition system usually will tolerate moisture but a leaky one won't.

[von.ah]

Thanks, guys. This is a lot of help. On my drive home from work I decided that tomorrow I'll swap the 1 & 3 cables and then see what gives. Regardless, this car is most likely due for new plugs/cables, since it's at 119k, and these have been in for at least 30k. Also, I purchased new cables from a dealer, so they're ready.

So, to recap:

If the misfire follows the cable, then it's obviously the cable at fault.

If I still get #3 misfire, the coil may be the problem, but couldn't it also be the plug?

As for the physics, I have read "The Elegant Universe" and "The Fabric of the Cosmos" by Brian Greene... :cool: Therefore I can safely state that regardless of what I may think is the cause of my automotive troubles, it's all just vibrating strings. And possibly there's a parallel universe in which my evil twin is tearing up Pike's Peak in a wickedly modified Outback. With a goatee, of course.

[porcupine73]

Welcome to the board! Did you try the water bottle spray in the dark method? Pulling the plug wires from the coil pack, soaking the coil pack with silicone spray, then reconnecting plug wires might help (it did for me once).

 

possibly there's a parallel universe in which my evil twin is tearing up Pike's Peak in a wickedly modified Outback. With a goatee, of course.

You're going to fit in just fine here..

[OB99W]

[...]If I still get #3 misfire, the coil may be the problem, but couldn't it also be the plug?

Yes, and there are also mechanical problems that can lead to misfire codes. (It could help to know under what conditions the misfire occurs; engine cold or warm, idling or driven, lightly or heavily loaded, etc.) Nevertheless, spark leakage is common enough to make investigating it worthwhile.

 

 

As for the physics, I have read "The Elegant Universe" and "The Fabric of the Cosmos" by Brian Greene... :cool: Therefore I can safely state that regardless of what I may think is the cause of my automotive troubles, it's all just vibrating strings. And possibly there's a parallel universe in which my evil twin is tearing up Pike's Peak in a wickedly modified Outback. With a goatee, of course.

We're all doomed to failure in our repair efforts anyway; the "observer effect" (not to be confused with Heisenberg's Uncertainty Principle) implies that looking into a problem changes it.

[crazyhorse001]

We're all doomed to failure in our repair efforts anyway; the "observer effect" (not to be confused with Heisenberg's Uncertainty Principle) implies that looking into a problem changes it.

 

Worse yet, the longer the diagnosis takes, the more the prognosis changes. Eventually everything returns to it's natural state. Unfortunately Subies, when left uncared for, tend to this more rapidly. I prefer cars that run well then die with a "Big Bang", only to be reborn into new star clusters. Every Subie I've had died attempting to discover what exactly happens when an irresistable force collides with an immovable object.

 

Ok I'm out of high level science metaphors!

[von.ah]

Yes, and there are also mechanical problems that can lead to misfire codes. (It could help to know under what conditions the misfire occurs; engine cold or warm, idling or driven, lightly or heavily loaded, etc.) Nevertheless, spark leakage is common enough to make investigating it worthwhile.

 

We're all doomed to failure in our repair efforts anyway; the "observer effect" (not to be confused with Heisenberg's Uncertainty Principle) implies that looking into a problem changes it.

 

Regarding ol' Heisenberg, I'm no Muad'Dib. :-\

 

Back on topic, the misfire happens warm or cold, driven under heavy load. "Stomping on it" in any gear will produce the miss.

 

By the way, thanks for the great welcome. This has been the coolest intro into any forum I've experienced. :cool:

[OB99W]

[...]Back on topic, the misfire happens warm or cold, driven under heavy load. "Stomping on it" in any gear will produce the miss.

Spark demands go up when cylinder pressures are higher, so that may increase the likelihood that there's an ignition problem.

 

The "wasted spark" circuit puts the companion ("paired") cylinders' plugs and wires in series; spark current for plug #1 also flows through plug #2, and that for #3 flows through #4 as well. (When one cylinder is firing, at the top of the power stroke, the companion is on the exhaust stroke; it only "wastes" a few KV to jump the gap of the plug that isn't under compression.) However, since the paired plugs are connected at opposite ends of a coil in the pack, the spark polarity is reversed for one versus the other. If I remember correctly, cylinders #1 and #4 wind up with negative at the center electrode, and #2 and #3 negative at the ground electrode. Since a spark can jump more readily from a hotter surface (the center electrode), all things otherwise being equal, it's easier on #1 and #4 than with #2 and #3.

 

So, a defect in the coil, etc. might affect the firing of a plug that has "reversed" polarity, but not the companion one getting "correct" polarity. In other words, a P0303 code doesn't necessarily mean that only cylinder #3 plug or wiring could be at fault. If you haven't already done so, check the wire resistance and connections to plug #4 as well, even if there's no P0304 or other evidence.

 

As I and others have already mentioned, looking for stray sparks and spraying down the coil, wiring and boots before digging in further could be worthwhile.

 

 

By the way, thanks for the great welcome. This has been the coolest intro into any forum I've experienced. :cool:

Glad you like it.

[von.ah]

It seems my luck is changing. I installed the new wires and that fixed the issue. No more rough idle, no misfire. Car runs like a bat outta hell now.

What's funny is that I tried just swapping the two on the passenger side, drove it to indice the misfire, but couldn't get the CEL to come back on. So I couln't tell which cylinder was acting up. Then I started getting facny with my DVM, and got totally confused by the resistance of the new wires. For identical wires, one measured ~11 kOhms, while the other measured ~140 kOhms. The old wires on that side measured ~ 10 kOhms. WTF? I was getting angry of course, so I just put in the new wires, it ran fine, so I'm happy.

Thanks for the help, guys.

[Cougar]

It seems my luck is changing. I installed the new wires and that fixed the issue. No more rough idle, no misfire. Car runs like a bat outta hell now. For identical wires, one measured ~11 kOhms, while the other measured ~140 kOhms. The old wires on that side measured ~ 10 kOhms. WTF? I was getting angry of course, so I just put in the new wires, it ran fine, so I'm happy.

Thanks for the help, guys.

 

It sounds like at least one of the old wires was intermittent. Using a ohmmeter to check for bad plug wires on problems like this has limited value in my book but it is all that most people have to check with. A scope would have told the story real quick. The high ohm reading you made of the new wire would make me think that you either had a bad meter connection to the wire or there really is something wrong with it's connectors. You should see numbers between 10k to 20k depending on the length of the wire, which the resistance is directly related to.

 

Glad you like the forum. There are a lot of helpful folks here that know what they are talking about. As you can see, there are some rocket scientists here also along with being great Sooby mechanics.

 

Good to hear you got your rocket engine running well.