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Discussion Starter #1
Hi. I know there is so much information on this forum about these codes but I have tried everything I could find and I need some help. During cold start-up and warm start-up (warm, after sitting 2 hours or more) I am getting a P0303 and P0304 cylinder #3 & #4 misfire. This is on a 2001 Outback, 2.5. Here are the steps I have taken so far;


New plugs (NGK BKR6E-11)
New Wires (Denso 7MM)
New coil pack
New fuel injectors
Adjusted Valves (.008"intake, .012" exhaust)
No loss of coolant
No loss of oil
Engine is grounded well in three locations


This problem popped up after changing my radiator and cap recently due to a radiator failure. The car was not over-heated when this happened. Just wanted to put that out there.


For about 500 miles prior to this I had a P0420 code that I was monitoring. I fixed a few exhaust leaks and had the O2 sensors checked and that still didn't fix this code, ultimately I changed;


Catalytic converter, resonator and muffler.


I also recently changed the camshaft position sensor and crankshaft position sensor due to other misfire codes showing CYL #1, 2, 3 & 4 cylinder misfires.


So...I have put a lot of time and money into this Subaru and I am getting very frustrated. Overall it runs well and gets good fuel mileage but I cannot get it inspected with this check engine light. I am just out of ideas to try and I am hoping I am overlooking the obvious. Any help is greatly appreciated.
 

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Discussion Starter #3
It is an aftermarket coil bought from Rock Auto. The coil was installed for 4K miles before this issue showed up. I replaced the coil 4K miles ago just because the vehicle has 160K miles and was 14 years old and I figured a new coil was a good idea. When the P0303/0304 problem came up, I put the original coil back on for troubleshooting without success. Since then I have reinstalled the newer one. The coil is under warranty and I could get another one...
 

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did you try re-seating the plugs / wires on those to cylinders?

someone else will pop up with something better. (maybe)
 

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Discussion Starter #5
Yeah, I even crimped the metal connector down inside the plug end so I could feel it "click" onto the top of the plugs. Once it starts, it actually runs nice. My daughter describes it as it "shaky, sputtering thing" when it starts...and it runs good once started. I ran Seafoam through it hoping it would help but it hasn't. My only thought is that the valves have carbon buildup on them...I read there is a product available for this but couldn't find the thread again...but I feel like I am grasping for things at this point...different sides of the engine has me thinking it may be electrical unless something else is common between the 3 and 4 cylinders...thank you
 

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Discussion Starter #6
Ok, so another update. The car appeared to be running normally (in the driveway). My daughter took it for a drive and as soon as she tried to pull out on the highway, it was missing terribly so she brought it home. No CEL was on but when I put the scanner on it, I got a P0304 Pending code. This tells me that all of my work recently touched something that made a difference because the P0303 is gone. On a hunch I bought new wires tonight online and will pick them up in the AM. I have this feeling that the wires are either breaking down or just not making good contact with the top of the plugs. I can't seem to push that rubber boot down far enough to get it to touch the valve cover so I am just guessing that the contact with the plug is questionable. I will post a new update after installed the new wires and going for a test drive.
 

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I have not read many using Denso labeled wires on these.

NGK and subaru sold "packard" ones only.

and subarus are very particular on ignition system brands.
 

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Discussion Starter #8
So I started with the suspect cylinder and BOOM! There was a unmistakable burn mark through the rubber boot about 3" up from the end of it. I proceeded to change that wire along with the other wires too. With each new wire, I felt the "click" as it snapped onto the top of the plug. Took it out for a quick 3 mile ride and so far, so good. I am getting ready to take it for a longer ride to see how it does. I am hoping the problem was just this simple because I have spent some time on this one. I would have never guessed that a set of wires would have failed so quickly but the proof is in the white burn mark on the #4 wire. I will post another update after the second test drive.
 

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what brand wires do you got in there now?
 

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Discussion Starter #10
The second test drive was successful, no misfire and no check engine light. The auto parts store had NGK wires so that was what I got. Quality seems to be my issue here. It was pretty clear that the #4 wire failed because the burn mark through the rubber was distinct. I lubricated up the outside of these wires so they would push down through the valve cover seal easier. I could feel the click when they snapped onto the plug; I couldn't feel that with the old wires.

This thread should prove useful for anyone troubleshooting a misfire on their engine. I covered most of the likely causes but mine turned out to be poor quality wires. It s a good idea to stick with NGK or Subaru ignition products and don't overlook the possibility that new parts will fail. Eagleeye, thank you for your input. You kept me rechecking the basics and luckily it turned out to be a routine part that is normally changed. Thank you!
 

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which autoparts store, did you find them in?

my local Advance does not seem to bother keeping NGK in stock,

although I typically buy from RockAuto or Amazon stuff like that as I can wait a few days.

emergencies do happen, with my car or someone I am talking to. (and putting Bosch plugs in a Japanese car, ...just does not sound wise).

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some of the parts on a subaru are denso stuff though, ...kind of generic things, and denso is a label made by many manufactures it seems. kind of like Dorman which you can find on like every factory car in the world.
 

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Discussion Starter #12
So the saga continues...my daughter just texted me a picture of a nice bright CEL on her dash again, UGH! I will investigate tomorrow and post the results.

Eagleeye, my Advance Auto parts had the NGK wires in stock so I was lucky.

My Subaru experience started out with a 99 Impreza, 2.2. The car never gave me a bit of trouble with auto parts purchased from Advance. I have always had good luck with Autolite Platinum and Delco wires. The next Subaru is a 2006 Forester. This car was very tolerant of the same type of auto parts. I got this 2001 Outback last fall...if it had been my first Subaru, it would be my last. This car has been giving me CELs ever since I got it. Every time I think I have it fixed, the CEL comes back. I have had misfires on and off and the dreaded P0420 code which has not been back for a couple of hundred miles.
 

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Discussion Starter #13
Quick update, the codes were P0303 and P0304 again. The car ran fine, no misfires were felt like the previous day. It seems like a nuisance code but it still needs to be fixed. At this point, since I can get the coil replaced for free, I am going to do that and see what happens. I have the original coil that I can put back on for a bit until the new one arrives. I am relieved that it is running fine despite the codes because I began to think the worst; head gasket leak, bad valve, etc.
 

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Discussion Starter #14
Eagleeye, so while I am waiting for a new coil to come (probably a week or so), let me bounce a few ideas off of you. First of all, when the car is started cold, for 1-2 seconds it runs a little rough but after no more than two seconds, the idle picks up, is smooth and the high idle kicks in. I am wondering if I have a fuel delivery problem? I hear the pump running but is it giving me enough fuel and the right pressure at start-up? This may be just another rabbit trail but when I compared it to my Forester, I found a difference in how long it would run after removing the fuel pump fuse. My Forester ran several seconds before dying out but this car died immediately, maybe 1 second but that would be all. I also noticed a rubber tube going from the #3 intake tube to what looks like a fuel pressure regulator. Just got me thinking about a possible fuel problem. One final thought for anyone out there...is there anything else common to the #3/4 cylinder other than the coil that would cause a misfire? Some sensor somewhere that would tie these two cylinders together? For now, I will wait for the coil....
 

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the misfires are going to get solved probably with the work / parts you are swapping in sooner or later.


you just replaced fuel injectors too,

did you replace the fuel filter under the hood?

here is a maint. schedule to compare what you know and have done to the car and to remind you what maybe lacking., it DOES NOT have a PCV valve or a thermostat on it that creates many a little problem. (but both those things have springs that get weak overtime and do need to be changed)

Subaru maintenance schedules and new car break-in period- 2000 through 2009, links for 2010, 2011...

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If you have not swapped a PCV in a long time, do not just take it out and clean it, swap it. ($18 for OEM, maybe $12 for something else). many a hesitation or ping is caused or augmented by a PCV.

how many miles on this 2001 H4? head gaskets done or not? (if so when)
@DavidPeab is one with a 2000 H4 that had his main fuel pump pop its cap while driving, and needed to replace it with a all new pump,
and he can describe if he had any funny starting problems just before, similar to what you are having now. the pump motor is still good, just the cap gets damaged when it blows off.

the rubber ring that holds the cap on degenerates and then the cap blows off,...some here have opted to swap the o-ring for a new one made of viton. @1 Lucky Texan has a 2003 H6 with the same pump, and he changed his out before it blew and stated the original o-ring was softening to a gel, vs. the new viton one he bought. (you can inspect and get at the pump from under the back passenger seat, on a nice day,....probably need to leave the windows open for a while to vent the gas fumes out of the interior).

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P0420 is a nag code with these, and sadly is not well defined or contained (I think a 2005 or newer subaru, one would get additional codes to trace it better).

it might just be a leaky exhaust,...such things happen when you put the car under load and something opens up before or around the cats.

you might swap the rear o2 sensor for a newer Denso and see it disappear, if it keeps coming back you got a larger undefined Air Fuel Ratio issue. I have 2 replacement o2 sensors on my H4, and rarely am getting a p0420, and just delete it ASAP so it does not force feed some gas trying to clear it on its own. (2 times a year).

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you might need to go at such things with Rom-Raider and a laptop. (free software, that makes logs for others to interpret). If the p0420 shows up more, I will go this route, vs. swapping good parts for more good parts.
 

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Discussion Starter #16
Ok, so I did replace the injectors on those two cylinders (3 & 4) but not 1 & 2 which has me thinking...the replacements injectors made a huge difference in how the car sounded at idle. With the old injectors it make a sound similar to knocking...the new injectors on those two cylinders made the sound almost completely go away and it idled much smoother. I just wonder if the injectors on the other cylinders should be replaced; not that it will directly affect my P0303 & P0304 code but maybe the sputtering at startup if from a faulty injector on 1 or 2...I did have P0302 codes in the past as well.


When we got the car I felt as if it had been neglected so I changed EVERYTHING; fuel filter, PCV, T-stat, coil, wires, plugs, CV joints/axles (both sides), wheel bearing...and sadly enough I have been troubleshooting ever since. When we drove it home it had a bad shimmy under acceleration and the CV joints fixed that. I drove it to work one day and filled it up on the way...7 miles later the CEL came on and has been an issue ever since. We never tried running premium fuel in ti to see if the misfire code would go away. Supposedly the timing belt was changed at about 130K...I am not sure if head gaskets were ever done on it. I would say, based on the corrosion on the valve cover bolts...no, the head gaskets are original. Currently 160,395 miles on the car. I have been wondering if the timing belt was a tooth off but the CEL for the misfire is more recent...but I guess I can argue that I have had some sore of misfire code ever since I got it.


Would a small exhaust leak at the exhaust manifold gasket cause a CEL for a misfire?


I have not had the P0420 code since changing the Cat and exhaust pipes so luckily I am not chasing that problem.
 

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what brand injectors did you put in?

Did you save the old ones? (I wonder if they could be cleaned up and reinstalled)

typically these don't actually fail on a car with only 160,000 miles.

maybe it just needed a spray of Seafoam. (the spray into the intake for $13,

not the old fashioned $7 bottle, which I would use after the spray by dumping on top of a tank of fresh gas).

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@1 Lucky Texan @cdc @grossgary @lockmedic @cracklincrotch @traildogck @rasterman
and other real smart wrenches might read though this and suggest something I am not thinking of.

did you inspect the hoses around the PCV for leaks (those get brittle overtime,)?

where is this car located in the subaru universe?
 

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Have you tested fuel pressure?
Or swap in another pump?

you can also swap injectors - just move them from cylinder 3 to cylinder 1 - if the misfire also "moves" with the injector then you know the injectors are the cause.
that said - subaru injector issues are rare. not impossible, but rare.

I'd be tempted to go back over everything too:

Aftermarket ignition coil and injectors?

I'm not sure if the igniter can cause issues with only two cylinders, but google that maybe?
 

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Discussion Starter #19
The injectors I used were remanufactured...when I changed them, the writing and part number on the old and new were exactly the same so I am hopeful they are good. There was a core on them so I don't have them anymore. No change in the misfire code before or after the injectors.


I did the seafoam in the gas but did not know about a spray for the intake. Will Advance carry it?


Hoses around the PCV valve...yeah, about that, I got my cars mixed up...I never found a PCV valve on this engine so it has never been replaced. Where do they hide it? I had a problem with a broken plastic tube that is crankcase vent related...coming up from the block is a rubber hose that goes into a plastic Y...this Y was broken. Off of the Y, one hose goes to the #3 intake manifold and the other goes to the air cleaner housing. I repaired the Y with epoxy because I couldn't find a replacement anywhere.


Located in Pennsylvania...


Grossgary, injectors and valve clearance was my "Hail Mary" play and the new injectors on these two cylinders definitely made a difference in the idle and the valves were just a little out of adjustment but neither were my smoking gun. I have read a lot about bad injectors on this forum...a friend of mine had 2 replaced on his Subaru and that fixed him up. At this point I am grasping at ideas.


Testing fuel pressure...how do you do it on these? My Ford was super-easy, just connect to the rail and start it up. This one looks like I have to "T" into it somewhere


Going back over it is what I am starting. I found a bad #4 plug wire, thought that was my smoking gun but it wasn't. Now I am waiting for a replacement coil to arrive...yes, unfortunately it is aftermarket.
 

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yes you have to T into those. rarely is low fuel pressure/output an issue but you've got a tough one here.

seafoam is available at most auto parts stores, my advance auto carries it.

you can spray around the intake manifold to check for vacuum leaks - but that seems unlikely as well. but at least it's easy and cheap.
 
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