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Old 01-19-2021, 11:14 PM   #426
demid30
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So I replaced my pcv valve on Sunday and this morning, 2 days later I get a check engine light with code p0304. Do you think it's related to something with the pcv I just replaced or is it a big coincidence that it's something not related to that? So frustrating.
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Old 01-20-2021, 10:37 AM   #427
subaru_gc8
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Quote:
Originally Posted by demid30 View Post
So I replaced my pcv valve on Sunday and this morning, 2 days later I get a check engine light with code p0304. Do you think it's related to something with the pcv I just replaced or is it a big coincidence that it's something not related to that? So frustrating.
nope, when was the last time you changed your plugs and coils?
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Old 01-20-2021, 07:08 PM   #428
demid30
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Originally Posted by subaru_gc8 View Post
nope, when was the last time you changed your plugs and coils?
I changed all 4 plugs 50k miles ago. I just did cylinder 4 coil and I still have the code. I didn't do plug because I only have 50k on them and now I'm pissed since I had it all apart. You honestly think it can't be something with pcv.
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Old 01-22-2021, 11:40 AM   #429
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Quote:
Originally Posted by demid30 View Post
I changed all 4 plugs 50k miles ago. I just did cylinder 4 coil and I still have the code. I didn't do plug because I only have 50k on them and now I'm pissed since I had it all apart. You honestly think it can't be something with pcv.
chances are no, if it were it would be a general code or all the cylinders would be misfiring not just #4
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Old 01-24-2021, 03:10 PM   #430
demid30
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Quote:
Originally Posted by subaru_gc8 View Post
chances are no, if it were it would be a general code or all the cylinders would be misfiring not just #4
Ok so I replaced all 4 spark plugs today and I did my air filter too as it also needed replacing. The spark plugs definitely needed replacing. Cylinder 4 spark plug was noticably worse then the other 3. So I go to check code and on torque pro it already was saying that my cylinder 4 misfire was fixed, it was highlighted in green with a check mark now saying historic code, which to me means it was now fixed. I cleared anyways and started car. It fired up great and idled great but 5 minutes later CEL started blinking again, but only cel this time, no cruise control and traction control lights flashing now. So I check code and it's the same P0304. So I say to my self I better check this PCV again. I take intercooler out and get the PCV out and guess what, the valve doesn't even rattle anymore. I tried cleaning it, it starts to rattle but then it won't rattle anymore. So I have to get a new PCV but have to wait to Subaru is open. What would cause this to happen to the PCV in 2 days?

Last edited by demid30; 02-04-2021 at 11:13 PM.
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Old 02-04-2021, 11:09 PM   #431
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I replaced the pcv and still have the p0304. So 4 new plugs and new coil on cylinder 4. This is frustrating, and ideas?
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Old 03-24-2021, 01:50 AM   #432
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on the way to check ..
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Old 10-05-2021, 09:34 AM   #433
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Default Delete

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Last edited by bjakiel; 10-05-2021 at 09:36 AM. Reason: Delete
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Old 10-05-2021, 09:35 AM   #434
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Default Misfire cylinder 3 in boost, not recorded when maf unplugged

Hello,

I have a 2013 sti.

I've been moving through the steps listed on this forum to diagnose my P0303 code. It only occurs in boost during WOT at around 3500 to 4000 rpm. The car shutters a bit and struggles, then the code is thrown.

On the MAF step, I've disconnected the MAF and have attempted to reproduce the misfire. My cobb accessport did not log any cylinder 3 roughness this time with the MAF disconnected. However, the symptoms where still present, maybe a tiny bit better. Does unplugging the MAF disable the logging of P0303 and cylinder roughness? Any hints other than continuing down on the list provided?
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Old 01-16-2022, 10:48 AM   #435
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Have a misfire on cylinder 4 only at hot idle, been through everything. Finally pulled valve cover to check valve lash. Here is what I had:

Int ft of engine 12 13 10 9
Ex ft of engine 12 9 12 11

From what I see .008” for intake +/-2 and exhaust .010” +/-2 and more people recommend on the turbo ej25 for the wrx .012” for exhaust. I have checked compression cold, 130psi all cylinders, #4 0% leak down, new pistons, borescoped no cracks on ringlands, swapped coils, plugs, rebuilt and swapped injectors, still no avail. Checked for vacumm leaks, or intake gasket leak, none. Even pulled off the extra valve cover venting hoses and routed off the intake to just atomosphere to make sure not and excessive blow by, still nothing. 91 tune filled with 93 and octane booster. Twice. Timing belt perfect. Cleaned Maf, added extra grounds, new coil pack connector on #4. 38psi fuel pressure at idle. Crank gear ok. Cleaned OCV on bank 2. Cam sensors and crank are clean.

New fuel filter and Walbro 225 pump. TD0516g blouch turbo, Catless downpipe, step one colder plugs, new coils, headgaskets, arp head studs, tgv deletes, new pistons and rings. Heads cleaned with new valve stem seals, valves just lightly lapped on the bench. Mishimoto turbo inlet, new pcv and hoses, spt intake. New timing belt and pulleys/tensioner. Stage 2 clutch with chromoly lightweight flywheel(14lbs though this could be issue, but it is only on 4). And cylinder 4 cooling mod. New O2 sensor. Extra grounds. 2 core radiator, mishimoto fans. Ebay unequal length headers and up pipe. Wrapped. Sti tm intercooler.

Tune by Eric and torque Performance

2006 wrx

Build has about 2,000 miles on it. Sometimes at idle hot it won’t count any roughness, and then sometimes it does. Counts as high as 30 on 4 and normally 4-12 when it isn’t as bad. Cylinder 2 will count sometimes up to 8 but rarely. Other side fine maybe 1-2 here and there but very rare. Will set a code for misfire on 4. Idles at 750 when it happens and if I bring it up to 1000 the miss goes away. Kinda at a loss on this one. I know my lash is off but I didn’t know if it was enough to cause my issue. Leaning towards electrical if I cannot find it here. But weird it can come and go and pull wiring harness all over and it makes no change.

When it happens at idle you can barely notice unless it counts up to 24-30 and you hear the little pop from the exhaust and feel it, when it is below 10 barely know unless you are looking at the accessport. I have been over everything twice and over a million forms and I saved lash for last and this is where I am at.

Any insight is greatly appreciated! Thanks!
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Old 04-30-2022, 01:29 AM   #436
K926
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Default Lightened flywheel issue

Quote:
Originally Posted by quazimoto View Post
5-10x a week an individual posts about having a misfire issue (MAINLY BECAUSE OF THE INABILITY TO USE THE SEARCH FEATURE!!!). This is a very common problem and there are alot of threads addressing this very problem. So here are the possible issues and solutions (read this first,then post about an issue if you have no resolution after trying said solutions):


MISFIRES


1. Wrong, worn or incorrectly gapped spark plugs. Generally NGK work best gapped between .028"-.030".

2. Clogged/dirty/bad injectors or fuel filter. Try changing the fuel filter. The maintenance schedule for the filter is every 30K miles. Have the injectors professional cleaned or at least run several bottles of a good injector cleaner through the gas tank. Also make sure you are using the correct octane gas! Either 91 or 93 unless you are specifically tuned for another octane!! (IE: race gas or E85) You can swap injectors from another cylinder and see if the misfire follows. If so this would indicate an injector issue if it does move..

3. Check valve clearances & compression. Perform a leak down/compression test first.The FSM has the valve clearance specs. This is a complete PITA with the motor in car.

4. Dirty or faulty MAF sensor. This causes an incorrect airflow readings. Misfires can result. Clean with CRC MAF cleaner or NON chlorinated brake cleaner. Make sure you are actually cleaning the MAF sensor and not just the IAT sensor. Common mistake.Also try swapping with a know good MAF to determine if the MAF is possibly bad.

5. Vacuum leaks or preturbo leak. Check where the FPR hose connects (generally you could get a P0457 or P0171 with this as well). Check the turbo inlet pipe where it connects to the turbo. This pipe is famous for ripping and causing a huge preturbo leak (P0171 as well).

6.Poor grounds/grounding. Clean the battery ground cable and ones that run to the intake manifold. Make sure all are connected. These are sensor grounds and must be kept clean.

7. Cam timing. Check cam timing per the service manual. Clean cam and crank sensor face.

8. Excessive PCV blow by. PVC gases will effectively lower the octane content of gasoline/petrol and can cause misfires along with knock. Get a catch can or air/oil seperater.

9. Carbon build up in heads/cylinders. You can use Seafoam or top end cleaner as well as other type of carbon remover.

10. Lightweight flywheels or crank pulleys. (phantom misfires) Can cause false misfires. Opensource tuning can disable.

11. Bad/loose coil pack or coil pack connector
. Test coil pack and move to other cylinder to see if DTC changes. If so this would indicate a coil pack issue. Also check the tower boot for corrosion.Make sure the connection to the coil pack is clean and tight. If the clip on the connector is broken,find a way to secure it.

12. Faulty fuel pressure regulator or fuel pump. Check fuel pressure. It should be bewteen 35-38psi idle @ sealevel. Removing the vac line at idle should give you 43 psi. The FPR is a 1:1 rising rate. For every 1 psi manifold positive pressure the fuel pressure should rise 1 psi.

13. Faulty front O2 sensor
Replace with new


14. Damaged crank timing gear

15. Misfires all cyclinders: Coil pack connectors mixed up (correct way:black to back,white to front),light weight flywheel,bad/unplugged crank or cam sensor,incorrect gapped plugs,cam timing off,bad front O2 sensor,poor grounding,fueling issue (fuel pump,fuel pump controller,FPR)

Flashing CEL (02-05 2.0L only) = Gross misfire. Doesn't always store as a DTC as it is momentary. For the most part diagnosis is the same as the above suggestions. This is more severe than the standard misfires and causes potential catalytic damaging consequences.

FYI-The bugeyes were plauged with misfires. Updating the ROM in the ECU to the latest revision from Subaru helps alleviate most false misfire issues. This can be done through the stealership or opensource software.

Hope this helps! Will add as other causes are found.
Hi, I know this is an old thread but I am a nooby and cannot post yet. I know a lightened flywheel can cause misfires cuz that's what happened to me. 2002 wrx. I am looking to see if anyone has came up with a fix to stop the low idle/misfires that trip the CEL. Or is this just something to expect and knowingly cannot pass smog once installed?
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Old 07-07-2022, 08:11 AM   #437
Jin3Mt
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Is this list supposed to be in order of most to least likely? It also doesn't specify CEL status.
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Old 07-25-2022, 09:23 PM   #438
dreinauer80
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Default Another mysterious misfire post

Greetings! I've been through all the common misfire causes to no avail. 2011 WRX GV, no engine mods/tune, not even an aftermarket intake. 214k miles. Top end engine rebuild at 168k miles, professionally.

I'm experiencing a misfire on all cylinders, codes P301-4. Running like a dream, no CEL codes in years, then started sputtering abruptly at a stop light.

All components of fuel delivery are good (fuel itself is clean, filter is clean, pump/lines/rails all good, replaced injectors and cleaned ports as part of troubleshooting with DW drop in replacements). Coil packs/connectors and plugs brand new OEM as part of troubleshooting. No sign of ignition wire nicks or issues. All grounds (that I'm aware of) in the car, battery, radio head unit (aftermarket) systematically checked. Cleaned MAF sensor, checked intake pathway for obstructions or boost leaks. Compression test near perfect (150-155PSI warm), oil is totally clean. Replaced timing belt and rollers as part of troubleshooting (Bank 2 intake cam gear off one tooth observed), no change. I unplugged the MAP, MAF, upstream O2, downstream O2, secondary air pump, AC compressor, systematically and restarted the car each time. No change.

The weirdest thing is it won't connect to the scan tool when running to see a live map. Using Snap-On Verus Pro tool. It connects and gets data, key on-engine off, but as soon as you turn it over something pulls it down and it doesn't send enough power to the scan tool and it errors. Never had an issue with this scan tool with any other vehicle. Leads me to believe the issue is electrical, like a needle in a haystack...can anyone hit me with common sensors or electrical issues on the stock car that may be causing this?

Another tidbit: It idles rough but won't stall at cold start, then gets worse as it warms up.

I'm at my wits end...car is in alleged perfect health for it's mileage, just doesn't run smooth. Send help.
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Old 09-16-2022, 12:04 PM   #439
Gamil
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Heads up on faulty crank position sensor:

It can be so intermittent that it passes all tests (ohm's and even oscilloscope). I couldn't confirm that was the problem on mine for 4 years until it degraded from misfire to crank-no-start, and the stars finally aligned so that I could read it with an oscilloscope while it was crank-no-starting.

It's a $20-$50 part, depending on which brand or where you buy. So, if all the other cheap/easy tests fail (compression, leak-down, fuel pressure, spark, timing, etc) then get a cheapo CPS off of rockauto, stick it in (it's fairly easy to access, at least on an EJ253). Drive the car around for a bit, and see if it clears up the misfire.
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Old 09-16-2022, 12:05 PM   #440
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Heads up on faulty crank position sensor:

It can be so intermittent that it passes all tests (ohm's and even oscilloscope). I couldn't confirm that was the problem on mine for 4 years until it degraded from misfire to crank-no-start, and the stars finally aligned so that I could read it with an oscilloscope while it was crank-no-starting.

It's a $20-$50 part, depending on which brand or where you buy. So, if all the other cheap/easy tests fail (compression, leak-down, fuel pressure, spark, timing, etc) then get a cheapo CPS off of rockauto, stick it in (it's fairly easy to access, at least on an EJ253). Drive the car around for a bit, and see if it clears up the misfire.
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Old 02-29-2024, 10:22 AM   #441
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I don't see it talked about here but my misfire was caused by the tune. Switched from side feed to top feed injectors on a 2005 FXT with TGV deleted, cylinders 2 and 4 were counting Roughness/Misfire when I was around 2600 rpm very low load like 30mph trying to go 35 but traffic in my way. Never threw a code but counted up to 10 and I could probably make it coint higher if I maintained that load and rpm.

I check spark plugs after 200 miles on the new type RA block and cyl 2 and 4 plugs were kind of oily and black. I thought valve seals but the heads were rebuilt 10k ago.

Well it turns out the Per Injector compensation tables were adding 10 to 15% fuel on cyl 2 and 4 in that range by default on a 2005 Forester XT.

These comp tables changed format for top feeds but was similar enough that I just took the 2007 FXT table and divided it by 100 to work with the 2005. It has more like 2% to 4% added fuel in these areas.

Some people zero out those tables, but you can convert like I did and it works.
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