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Old 11-24-2012, 05:47 PM   #1
salvi
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Join Date: Aug 2008
Default P0302 and P0303 engine miss fires after swap, help!

I've been fixing all the issues that I've been getting with this swap on my GC8. The motor is a fresh rebuild, both the heads and block.

Right now I'm throwing two miss fire codes for Cylinders 2 and 3. The car idles really rough and sometimes doesn't even want to turn on.

**What it has been done/has new
1. New Walbro 255 fuel pump
2. New OEM fuel filter
3. All injectors were sent out for cleaning and flow tested
4. Brand new NGK spark plugs all around
5. Brand new under intake fuel lines since they were leaking

**What I've troubleshot
1. Replaced the MAF from my bugeye, issue still present
2. Removed two known good coils from my bugeye and installed them on the Cylinders throwing the codes, issue still present
3. Removed both spark plugs from those cylinders, they looked fine
4. Since intake mani was powdercoated, i removed the powder from the two ground points on the intake manifold. Issue still present

I'm at a loss of what else to do/check. I have the WRX that I can take parts from for testing. Please give me any advice/ideas on what to do.
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Old 11-24-2012, 06:02 PM   #2
danger1138
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Location: QUEENS NY
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04 rex luger!

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Try ensuring 100% that the clips going onto the coilpacks have the white wires going to the front & black wires goin to the back coilpacks. Also ensure the wires are fully connected. I once was missfiring when i removed my spt intake and i was goin nuts. Just happened to be i had pulled the wire going into the # 3 cylinder coilpack, pushed it in (fully connected) while was idleing and suddenly smoothed out. Also what gap are the plugs set to? Maybe try closing the gap a bit
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Old 11-24-2012, 06:05 PM   #3
salvi
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I made sure that the white plugs are in the front and the black in the rear. The plugs are also all connected properly. I even made sure they clipped in place and pushed them additionally.

The plugs are the iridium plugs and they are pre-gapped and cannot be gapped.
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Old 11-24-2012, 06:08 PM   #4
danger1138
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04 rex luger!

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How bout tgv's maybe some of the flappers are stuck closed
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Old 11-24-2012, 06:11 PM   #5
salvi
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Hmmm...I did remove the TGVs to get the intake manifold powdercoated, but I made sure to install everything properly. How can I test that the TGVs are an issue? Wouldn't it be throwing a TGV cel if that was the case?
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Old 11-24-2012, 06:17 PM   #6
danger1138
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04 rex luger!

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So your saying you still have the stock tgvs right. Well ive checked on my cobb AP, and one side of the tgvs read a certain voltage dont remember, something like .4. The other side read 0. And thats the side i was getting a missfire on. Cylinder 4. I later went ahead and deleted them now i have no missfires. Knock on wood!
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Old 11-24-2012, 06:49 PM   #7
salvi
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Yep, stock TGVs. I removed the motors when the intake was off the motor and they all moved fine. I re-installed them according to the manual. I'm not getting any TGV cel though. Were you getting a TGV cel?
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Old 11-24-2012, 06:54 PM   #8
danger1138
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04 rex luger!

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No i wasnt getting any tgv related codes. Maybe it was 'tuned off'.
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Old 11-24-2012, 06:56 PM   #9
danger1138
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04 rex luger!

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How are the injectors? Did u use new ones? How are the o rings? Maybe a leaky injector
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Old 11-24-2012, 08:08 PM   #10
salvi
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How can I test the TGVs with the motor turned on?
Injectors are stock WRX and they were sent out to clean/flow tested. All orings on them were replaced.
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Old 12-02-2012, 03:10 PM   #11
RallyBot 6.0
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Location: MT. HOOD Vancouver, WA
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hey im throwing the same code right now, P0303. 02 wrx with 04 motor/trans pretty much stock. the code will only come up like every 400 miles after i clear it or if im driving it really hard. only time i have actually noticed it was at WOT in like 4th gear the rpm guage dosnt move at a constant speed, every 500-1000 rpm's it will slow down for like 1 sec then start moving at normal pace again.
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Old 12-02-2012, 03:19 PM   #12
RallyBot 6.0
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i did take my intake off to start building a custom shield and did move around some wires but i dont know which wires have to do with the coil packs
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Old 12-03-2012, 09:02 PM   #13
salvi
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FYI, my issue ended up being a timing issue. After checking/testing everything, I removed the timing cover and the timing was off. Removed/reinstalled the belt with the correct timing and now it's running perfect.
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Old 12-04-2012, 08:36 AM   #14
04ScoobyWtf
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I know in my Lexus I got a bad misfire when I get low on gas. You can try some fuel tank cleaner. Maybe get some out. I would also change the fuel filter after just in case
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