CEL course of action? (Updated 01-12)

[DonMarcoPolo]

Got CEL yesterday, got it scanned @ autozone: #4 Cylinder missfire. What is the first thing I should do? My first thought is new plugs/wires, but I don't wanna just throw parts at it and have that not fix it. Any help would be appriciated.

[Huffer]

What was the actual code?

You should pull the plug on #4 and check the condition of the plug. It could be loose, mis-gapped or something minor.
You could just buy one plug just in case.

[DonMarcoPolo]

ty. I'm actually about to go out and do the snorkusectomy and see about switching over my headlights. I'll check that while I'm out there.

[jey]

I'd clear it and see if it comes back, and if it does if it comes back on the same cylinder or a different one. That will help narrow things down a bit.


You could just buy one plug just in case.

Really? I would think that there are enough variances between the performance of plugs as far as age, and even between brand to brand (so if you happen to get a different brand) that it would be a lot better to replace plugs all at once. In fact I think they come in packages of 4?

[Huffer]

You're probably right - and given the cost, it's pennies. :)

[DonMarcoPolo]

So, after I replaced all 4 wires and plugs, the CEL went away as well as the rough idle and didn't come back...until a few days ago. This time, it was preceded by a lurch when i tried to get heavy on the gas to merge with some traffic...the power just totally went away for a moment. On top of that, it idles so rough now that the first stop I could make, I got out and checked to see if like 1/2 of my engine was missing or something, lol. I'm quite worried that this is gonna cost me a chunk of $$. Any input / help?

[2000gtb]

no CEL this time????

[DonMarcoPolo]

ya, got CEL with same code as before.

[Robbks]

Which vehicle
the L or outback?

[DonMarcoPolo]

Outback

[DonMarcoPolo]

Bump

[httrdd]

Do you have a coil pack on that year outback? If so there could be a short there!

[DonMarcoPolo]

yes, and no short. I read primary & secondary. all good. also read injectors while I was there...they are all good too. As much of a P.I.T.A. as it was to get those plugs out, I think its time to hook a compression tester up to it...(sigh).

[Robbks]

How does the ECU know it's a mis-fire?
i assume it can only know that it has not been given a crank signal when it was expecting it, and as such the ECU itself has not fired the coil.

try swapping the crank sensor with another known good one.

[DonMarcoPolo]

Well a fresh update seems to be an order. I found I was getting absolutely no compression in Cyl #4, so I got it checked out. Long story short, 2 burnt valves, new head-gasket, $2200, and a smooth runner yesterday morning. Then on the way from work this morning, CEL again....#1 misfire (this is after it went from #4 to #3 while in the shop. I'm thinking now that I may just get a new coil (ignition coil resistances don't match what my book says they should be)...and its like a $30 part.

If I didn't effin love this little car, it just wouldn't be worth it. I just can't argue with its overall condition for its age (or for any car for that matter).

...more updates as I get 'em.

[ouch1011]

How many miles on this engine? Valves typically don't burn by themselves, but on engine with solid lash adjusters like pretty much all Subarus since 96, wear on the valve seats or stems can cause the valve lash to disappear and the valves to be held open slightly, which causes a loss of compression and will burn the valve. Typically this doesn't happen though unless something causes excessive wear. Has the engine had any prior head work? If someone has adjusted the valves before, they may have adjusted them too tight (not enough clearance) and caused a burnt valve that way.

BTW, to whoever asked, the PCM determines an engine misfire by monitoring engine speed at a high resolution. Engine speed is not steady, it is constantly fluctuating rapidly up and down, especially at idle (we feel it as a vibration). The PCM knows when a cylinder should be firing and it expects to see the engine speed go up when this happens. If it doesn't, or it drops, it logs it as a misfire. The Ford scantool does a good job of providing a visual of this...

http://www.youtube.com/watch?v=JDexfNY0JwU

In that video, cyls 5 and 7 are misfiring.

[DonMarcoPolo]

How many miles on this engine?

Just broke 94k. So far, I've made it about 200 miles without another CEL since I replaced the ignition coil (which was more like $70, instead of the $30 that I said earlier)...fingers crossed. Still idles a little rough though, but runs like a champ.

[DonMarcoPolo]

Argh....well, P0301 is back again (Cyl #1 Misfire). This is drivin me effin crazy! I'm supposed to be taking this thing to Montana for my vacation on Wednesday...$#%@!!! OK, so lets recap just for fun, so maybe ya'll could help me narrow down the posibilities:
*New head gaskets
*cylinders #4 & #3 had burned valves (so I'm told)
*new timing belt
*new spark plugs & wires

...whats left? There's only 94k on this engine now...WTH COULD IT BE?!?!

[jey]

Have you checked for vaccuum leaks? Replaced the fuel filter yet?

[ouch1011]

When does it misfire? Idle? Under accel?