cylinder 1&2 misfire mystery

[krotki]

I have a 97 Outback (2.5) with 100K miles. Recently the Check Engine (CE) light has been intermittently turning on. The codes that I get from a scanner are cylinder 1 and 2 misfire. The CE light mainly comes on at highway speeds after driving for a while. At times the light will even flash before going to a solid orange. The strange thing is that even when the CE light is flashing there is no noticeable change in the engines performance/operation, the car drives normally! If I drive around town for a day without getting on the highway the CE light turns off. I have replaced the spark plugs, spark plug wires, coil pack, fuel filter and air filter. I have checked the engine timing, compression, fuel injector operation, cam and crank sensors etc. Nothing shows up as a problem but the CE light still comes on.

 

 

If anyone has any suggestions/ideas I could really use some help before I give up and take the car to the dealership.

[frag]

The ECU spots a cylinder misfire by registering a slight engine deceleration just after sending the spark to that cylinder. This means that ANYTHING that will cause the cylinder to produce less energy can trip a «cylinder misfire» CEL.

The cause can thus be almost anything: ignition (plug, wire, coil, ignitor), fuel (mainly fuel injector cause a low fuel pressure would have the same effect on all cylinders), mechanical (valves).

I'm afraid you just have to continue testing till you've made a round of all those components.

My two cents.

P.-S.: the fact that the misfire is related to two opposing cylinders points to a coil problem, but you have replaced that. Maybe the ingnitor. But I'm not familiar with the way the ignitor operates and if it's likely that it could go bad on twoopposing cylinders at the same time.

Good luck!

[Cougar]

This may be due to carbon buildup. You could also try using premium gas to see if that helps with this problem. If you aren't using NGK plugs already I would get a proper set installed.

[Commuter]

I have a 97 OB as well. Mostly highway miles; now at 410,000 km.

 

Yes, these engines are prone to carbon. I've gone thru the issue a couple of times. It takes something like a MotorVac to properly deal with it. After that, you can keep things in check with premium fuel, or cleaners. The sympton I got was low rpm hesitation. (eg 600 to 1000 rpm.)

 

I don't know if this is related to your misfire problem, but it could be as has been pointed out.

 

Have you ever changed the O2 sensor? My carbon issue slowly went away the last time after I changed mine out (about a year or so ago). They said it was ok (but a bit slow) and I wasn't getting any CEL, but I decided to do it anyway. It saved me having to do a MotorVac again. My last e-test looked better too.

 

Commuter

[Adnan]

Hi,

 

I vote for the ignitor too. They are usually made with IGBTs as the actual switch and these can, over time, develop high leakage and thermal-related problems. High flyback voltages from the coil could also damage them but that's less likely.

 

Regards,

Adnan

[WAWalker]

The valves on these engine need to be adjusted. The Maintenance Manual says 105,000 miles.

Tight valves WILL cause the problem you are describing. If they are left tight for too long they will burn.

[charlierh2]

try seafoam through a vacuum line it works wonderfuly on the carbon buildup:brow:

[lshelley]

I have the same problem but the scanner says cylinder 3/4. I think -frag- has hit on something I didn't think about. My CE light comes on at highway speeds (70-80mph) with no noticeable hesitations. I have noticed it happens when I take pressure off the accelerator just slightly. Like just topping a hill. It may blink for 3-5 secs before going solid. If the ECU is detecting an engine deceleration (I took pressure off the accelerator!!) just after sending a spark I don't see a fix unless a time delay can be changed in the ECU.