newsance Posted June 3, 2009 Share Posted June 3, 2009 Ok, so for the past month, I have been getting a recurring P0304- Cylinder 4 misfire detected. It typical happens at idle or low load. It seems to accelerate fine. At first it was occasional, but has been getting more and more prevalent. I'm at wits end trying to take care of this. I've replaced spark plugs, wires, coilpack, and fuel filter. I've swapped fuel injectors with a different cylinder- no change. Compression test shows 150 PSI on the cylinder- same as the others (I live at 7,000 feet- the cylinder pressure is typical). I've cleaned out the EGR valve and checked that the valve wasn't stuck. I haven't checked the EGR solenoid because I'm not sure how. I need other suggestions. Thanks! Quote Link to comment Share on other sites More sharing options...
211 Posted June 3, 2009 Share Posted June 3, 2009 I'm throwing up the exact code (misfire Cylinder #4) I'd have to run a search again since I don't remember the exact thread but for one guy with a similar problem it ended up needing a valve adjustment. How many miles are on it? One thing you can do is swap cylinder 4's wire with cylinder two and see if the misfire code changes location. That will rule out a bogus plug. Otherwise I'm curious to know what you come up with; as I said I'm throwing the same code Quote Link to comment Share on other sites More sharing options...
newsance Posted June 3, 2009 Author Share Posted June 3, 2009 I've already changed the plugs and coil. Its not the coil. I would expect that if there was a valve adjustment issue I would also have a compression issue, correct? Quote Link to comment Share on other sites More sharing options...
OB99W Posted June 3, 2009 Share Posted June 3, 2009 Ok, so for the past month, I have been getting a recurring P0304- Cylinder 4 misfire detected. It typical happens at idle or low load. It seems to accelerate fine. One possibility is an intake air leak. That would have the most effect at idle, since at higher speeds/loads, the larger volume of air being used by the engine ''swamps'' out the leak. I've cleaned out the EGR valve and checked that the valve wasn't stuck. I haven't checked the EGR solenoid because I'm not sure how. Much of the time, EGR valve problems are from the valve not opening or passages being blocked with carbon. However, if the EGR remains open more than it should, that can cause misfire, and sometimes doesn't trigger an EGR code. Quote Link to comment Share on other sites More sharing options...
newsance Posted June 3, 2009 Author Share Posted June 3, 2009 I'll check again for leaks. The EGR valve looked like it had a good seal, and wasn' that dirty. Thanks for the suggestions. Quote Link to comment Share on other sites More sharing options...
OB99W Posted June 3, 2009 Share Posted June 3, 2009 I would expect that if there was a valve adjustment issue I would also have a compression issue, correct? A good compression reading will confirm that the valves are closing (sealing) correctly. However, compression testing won't reveal if a valve isn't opening sufficiently, unless the condition is very severe. (Intake valves not opening enough could require more crank rotations to build up cylinder pressure than on cylinders with correct valve adjustment.) Quote Link to comment Share on other sites More sharing options...
OB99W Posted June 3, 2009 Share Posted June 3, 2009 I'll check again for leaks. The EGR valve looked like it had a good seal, and wasn' that dirty. Thanks for the suggestions. You're welcome. While you're at it, verify that the PCV valve isn't sticking open -- that can have the same effect as an intake air leak (leans the mixture, possibly causing misfire). Quote Link to comment Share on other sites More sharing options...
unibrook Posted June 3, 2009 Share Posted June 3, 2009 replace your front 02 sensor if it hasn't been done in the last 40k miles. trust me. do it. u will thank me later. Quote Link to comment Share on other sites More sharing options...
OB99W Posted June 3, 2009 Share Posted June 3, 2009 replace your front 02 sensor if it hasn't been done in the last 40k miles. trust me. do it. u will thank me later. An aging O2 sensor can cause the mixture to run rich, but that doesn't usually lead to misfire. However, at significant altitude (where the air is ''thin'') it might be possible for that enrichment to be sufficient to cause rich-misfire. Properly diagnosing the problem should probably include an OBD-II scan tool, looking at sensor performance, fuel trims, etc. Quote Link to comment Share on other sites More sharing options...
bratgrl Posted June 9, 2009 Share Posted June 9, 2009 My friends 98 Legacy wagon is giving her this same code. It comes and goes, and she says it comes on when she is going about 75 to 80 mph, Sometimes it will stay on for a little while and then go out, and sometimes it comes on and stays on for days. She has paid her mechanic hundreds of dollars to diagnose and correct the problem. None of his "fixes" so far have worked. The latest fix last week lasted for about 10 miles down the road. She says he has checked EGR, PCV, and a whole bunch of other stuff she can't recall. I will be watching with interest to see what you guys come up with. Quote Link to comment Share on other sites More sharing options...
CarolinaPilot Posted September 5, 2010 Share Posted September 5, 2010 Hi Guys-- I am having the same P0304 situation but the CEL blinks from time to time. Not at idle but driving down the road. I don't know if it is an injector or valve issue as already mentioned. Differently know it happens as you know there is a loss of power. Our 1997 Subaru Legacy Outback has a 2.5L motor, auto tranny, and 157K miles that we have owned new from day one and have done all the maintenance on this car ourselves except when the head gaskets needed replaced 3 and 1/2 years ago. I have replaced the spark plugs and wires with all Subaru OEM stuff. I have pulled the spark plugs they look fine and no oil is seeping in around the spark plug boot or wire from the valve cover. I have sprayed water on the coil pack and wires in the dark and have seen no electrical leakage. We have pulled out an automotive stethoscope and have listened to both injectors on the same side of this boxer engine and they sound fine even when the RPM is changed. Vacuum is good and I have found no restrictions. I have even drawn 1/2 a bottle of Sea Foam into the manifold. Got a good smoke out of the tailpipe but did not change anything. How do I track down this intermittent problem, keep the CEL off, and give confidence back to my wife to drive this car? I probably think a I need to swap injectors around, but not sure which other cylinder injector on the motor to swap with. About How much would it cost to to have the valves adjusted? Do the heads need to be pulled to adjust the valves? I am starting to reach the limit of my technical bandwidth. Any additional ideas for suggestions not already mentioned would be appreciated. Thanks Quote Link to comment Share on other sites More sharing options...
CarolinaPilot Posted September 6, 2010 Share Posted September 6, 2010 I making a big stretch here, I am I going down a good path to problem-solve? If I could bring home an oscilloscope to hook up to the injectors to look at their individual firing, does anyone know what frequency I turn the O-scope to so that I could show the square wave of firing? Quote Link to comment Share on other sites More sharing options...
OB99W Posted September 6, 2010 Share Posted September 6, 2010 (edited) Since you said you can hear the injector pulsing, it's obviously getting turned on and off electrically. Therefore, I'm doubtful that a oscilloscope will reveal anything useful. A voltmeter or noid light would probably tell you enough. As to swapping injectors, pick one that's convenient. However, to answer your question, each injector is pulsed at a rate equal to half the RPM of the engine (since it's a 4-cycle) -- to get pulses per second, divide RPM by 120 (60 seconds per minute, 2 revolutions per pulse). Choose an appropriate scope sweep speed based on that, or just switch the horizontal timebase until you see a reasonable number of cycles. At idle, it will be pretty slow (example: 600 RPM divided by 120 yields only 5 Hz pulse rate), and might require a scope with either long persistence or storage to easily see. Could you elaborate on "vacuum is good"? What was the reading at idle and higher speeds, up to about 2,000 rpm? How steady is the reading? What's your elevation? As mentioned previously in this thread, valve contribution to misfire can be due to either not sealing correctly or not opening enough. (That assumes there's not a timing issue, which is less likely since you aren't seeing a problem with cylinder #2.) If there's a leaky valve, a drop in vacuum will occur each time the problematic cylinder is operated -- the amount of drop is dependent on the degree of leakage. Some vacuum gauges have a very small orifice, and aren't a good indicator because they tend to average/smooth the measurement. Especially if the vacuum reading is inconclusive, a cylinder compression and/or leakdown test could be helpful. EDIT: See for injector info: http://hp.auto.ru/Subaru%20Legacy/1997/Service%20Manual/ENGINE%20SECTION/FUEL%20INJECTION%20SYSTEM/ Edited September 6, 2010 by OB99W Quote Link to comment Share on other sites More sharing options...
SuBrat84 Posted September 6, 2010 Share Posted September 6, 2010 I sure would like to see a solution to this issue as it seems to be more and more common on here. I have thrown a bunch of stuff at my '97 2.5l trying to figure it out. The last suggestion I was given was to replace the ignitor (Behind the intake manifold on the firewall.) I haven't done it yet because I'm flat broke. HOWEVER, the other night we were driving around in the flooding and I got an injector #1 voltage HIGH code... instead of the typical 1&3 misfire codes that I get when it's really hot out and I drive for more than 1/2 an hour. Quote Link to comment Share on other sites More sharing options...
CarolinaPilot Posted October 17, 2010 Share Posted October 17, 2010 Our 97 Outback with the 304 error were told it turned out to be a burnt exhaust value and loose valve guide. Engine runs good but the check engine light is still on. After getting it home, our check engine scanner showed a P0403 - Exhaust Gas Recirculation Circuit Malfunction. When we took it in, it was not blowing this code. What causes this? Vacuum lines and hoses not routed correctly? Any help would be appreciated. Thanks. Quote Link to comment Share on other sites More sharing options...
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