steamin53 Posted January 4, 2009 Share Posted January 4, 2009 I'm really not into fixing cars by phone..heh heh... but my daughter has my wife's 96 Legacy Outback 2.5 out of state right now and is experiencing a misfire on cylinder 2 with roughness in idle and acceleration. DTC P0302 verified by OBDII scan at local car parts place. Idle speed control appears to be working correctly or so they say. The engine is a CCR rebuild with about 20K on it which means the plugs were new on rebuild. This is not a bogus check engine light but an actual misfire, or so it appears due to the rough running engine. I had the son in law disconnect the battery to clear the PCM and the problem went away, engine ran smoothly, but after driving some distance the problem returned. Here's my questions. 1. Since the problem resolved temporarily after clearing the PCM and the engine ran smoothly I must assume that the plug and plug wire is ok. Right? 2. Since it's only one cylinder misfiring I must assume that it's not the coil because as I understand it the coil fires to simultaneously to cylinders 1 and 2so I if it were bad I should expect misfires on both cylinders or at least constant misfires on either 1 or 2 that would not resolve after clearing the PCM. Right? Of course the output of the coil to the number 2 spark plug wire could be intermittently bad. 3. Since the coil fires simultaneously to cylinders 1 and 2 could I swap those wires on the coil to see if the problem follows the swap and moves from a cylinder 2 to a cylinder 1 misfire code? 4. The igniter is not at fault because it functions correctly after clearing the PCM even though the problem reoccurs after some driving. Right? 5. The MAF sensor is not at fault because all cylinders are not affected. Right? HELP! Link to comment Share on other sites More sharing options...
johnceggleston Posted January 4, 2009 Share Posted January 4, 2009 move the wire front to rear to see if the problem moves. i have an occasional mis fire whe nthe weather conditions are just wrong, usually when moisture is condensing on the engine due to a rapid weather / temp / moisture change. it happens so rarely, i haven't bothered to chase it. about once a year, when the weather is really damp, foggy, wet, rainy, i'l get a cel and a rough running engine, it usually includes a blinking cel. and this last time i wondered if the engine was going to die. i kenw what it was so i didn't bother to check the code. when the car warmed up / dryed out it ran better, when the weather dried out it ran fine. no blinking after the first day. 2 weeks later the cel went out. when i finally checked for the code it to was gone. what's the weather like where the car is. too check your car for this condition. use a water mister to spray a mist around the coil, wires and plugs at night. if there is an electric leak, it will show up. back in the old days when the wires & dist cap on my 60 chevy pickup leaked, i'd spray them with a silicone something to help seal them up. worked short term. i have no idea if it would today. were the wires new 20k ago? were they subaru wires? good luck. Link to comment Share on other sites More sharing options...
3Pin Posted January 4, 2009 Share Posted January 4, 2009 I agree with your logic and try swapping wires first. After that, it could be the plug, coil or a burnt valve. Try the easy stuff first though. Link to comment Share on other sites More sharing options...
idosubaru Posted January 4, 2009 Share Posted January 4, 2009 very common, most likely the ignition wire is compromised. Note - do not replace it with anything but Subaru wires. Aftermarket wires are crap. If you have to replace it with something like that now, plan on getting a set of Subaru wires as soon as possible. I've seen brand new aftermarket wires right out of the box cause cylinder mis-fires. This isn't true of all Subaru's, but this engine it is. Wouldnt' surprise me if the existing wires are old or non-Subaru replacements. Usual cylinder misfire causes: Plugs/wires Ignition coil Link to comment Share on other sites More sharing options...
steamin53 Posted January 4, 2009 Author Share Posted January 4, 2009 What I DON'T understand is how resetting the PCM can temporarily "cure" the problem. If the coil or plug wires, or in fact, any of the ignition components were the cause wouldn't the problem persist despite resetting the PCM? After all, the PCM does not actually control the state of the coil, and certainly not the plugs or wires. I'm baffled, but leaning toward something other than ignition now. I had some idle air control system problems which I thought I had fixed with another idle air control valve, and ultimately a different PCM. But that was months ago. As I recall however, the PCM has a limp mode that reduces a fast idle RPM condition by disabling spark to (hmmmm cylinder 2?) in order to prevent engine damage. Problem with that is that they report no such high idle state to manifest that action by the PCM. Stumped! Link to comment Share on other sites More sharing options...
johnceggleston Posted January 5, 2009 Share Posted January 5, 2009 i wouldn't be too surprised, lots of electrical problems are intermitten at first, or only under certain conditions. Link to comment Share on other sites More sharing options...
idosubaru Posted January 5, 2009 Share Posted January 5, 2009 What I DON'T understand is how resetting the PCM can temporarily "cure" the problem. you're over thinking this and ignoring the advice of people who know a lot about these engines. what kind of wires are on there now and how old are they? your wires likely need replaced. i'm not well versed in the ECU, but maybe this will help. the ECU doesn't typically trigger a code with every reading out of spec. often it requires "X amount of faults over a given period of time". so codes disappearing after resetting the ECU makes perfect sense...it's going to need that "given period of time" to analyze data and trip the code. and - the ECU has two modes - open and closed loop based on whether it's at operating temperature or not. they way it detects codes and uses data during those two operating parameters differs. and - electrical problems are often directly related to temperatures..not just ambient, but when in use electricity/shorts can generate heat - so if they went away and came back after various cycles of starting/turning off i'm not surprised either. that's basic electrical concepts. conductivity is highly dependent on temperature (and hardly anything else for metals we're talking about). and on and on.... all of your symptoms look completely normal and very common to me. this isn't rocket science, but i can go there too if need be! Link to comment Share on other sites More sharing options...
john in KY Posted January 5, 2009 Share Posted January 5, 2009 Your problem sounds exactly what I experienced a few weeks ago except never got a trouble code. Turned out to be a short in the coil pack. Link to comment Share on other sites More sharing options...
steamin53 Posted January 11, 2009 Author Share Posted January 11, 2009 (edited) Well we solved the problem. NEVER IGNORE THE BASICS. The number 2 cylinder plug wire had somehow come unattached from the plug. Bizarre if you think about it as it's been untouched since the engine was installed several thousand miles ago...go figure. I would have caught it if I had been on location but my son in law is a software engineer and not mechanically inclined and he missed it. As soon as I had him start it in absolute darkness it was clear that there was an arc to ground in proximity of the cylinder 2 connection at the coil. Removing the cylinder 1 wire from the coil stopped the arc (no discharge of the field from that coil because ground is removed) proving an open to ground on the cylinder 2 wire. Simple investigation of the number 2 wire found the problem. Reconnection of the wire and the car runs better than ever. I agree the plug wire must not be in the greatest shape and that they need replaced or the arc could not have occured through the insulation of the number 2 wire to ground. I always over complicate things. Again, NEVER FORGET THE BASICS. Thanks to all. Steve Edited January 14, 2009 by steamin53 grammer Link to comment Share on other sites More sharing options...
idosubaru Posted January 11, 2009 Share Posted January 11, 2009 awesome, easy fixes are awesome. I would have caught it if I had been on location but my son in law is a software engineer and not mechanically inclined and he missed it. hey, wait a second! i'm a flight software engineer, some of my code and patches are zipping around in NASA birds as I type. deep man, deep wounds. i did forget to install that washer on my friends legacy just last night and had to take it apart...hmm... Again, NEVER FORGET THE BASICS. and listen to goobs that have learned this stuff the hard way (finger points to me)...lol.....very common, most likely the ignition wire is compromised. Link to comment Share on other sites More sharing options...
steamin53 Posted January 14, 2009 Author Share Posted January 14, 2009 Grossgary, you haven't met MY son-in-law. He get's Patriot missiles to shoot down scuds and more but drove his 280Z for years with a screw driver in the throttle to keep the choke plate open. I'm just glad he found it. Steve Link to comment Share on other sites More sharing options...
Recommended Posts
Please sign in to comment
You will be able to leave a comment after signing in
Sign In Now