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Old 02-05-2019, 10:37 AM   #1
Scooby Newbie
Member#: 206421
Join Date: Mar 2009
Location: Central NC
2003 wrx

Default 2003 WRX flashing CEL on cold mornings

`03 WRX, 243000 miles, stock except for aftermarket clutch and smaller flywheel that was installed about 18 months ago. 93 Octane fuel. Oh, I did put a Mishimoto rad in it at about 120000. I am the only owner of the car.

Flashing CEL at times. It will happen when the engine is ~cold, i.e. only been running about 5 minutes. I can shift up through the gears fine, and when I get to fourth and give it moderate throttle, the CEL (sometimes) starts to flash. I will back off, but it keeps flashing for a few seconds. Sometimes the light goes away altogether, and sometimes it stays illuminated. Each time I've read the code, it shows a cylinder misfire (I don't recall if it's one cylinder more-often than another).

There have been 2x instances where the CEL flashed on a very warm (>15 minutes of driving) engine. Both times it happened when I was in fourth and demanded a little more power to climb a hill, accelerating from about 45mph to approaching 60.

From what I've researched on here and other web sources, I've concluded that the aftermarket flywheel -which is smaller than stock- is causing the sensor to detect a misfire. I didn’t have this issue (flashing CEL) before the new clutch was installed. With that in-mind, I haven't lost much sleep over it. However, now that the weather's cold, it happens a bit more frequently. It doesn't happen in the summer months. Ultimately, I'd like you guys to put my mind at ease and tell me not to worry about it, because reading some of the "flashing CEL" threads is scary.

FWIW, I'm very unhappy with this aftermarket clutch/flywheel (I don’t remember the brand right now). I wish I had gone back with the stocker, but the shop talked me into this "performance" part. That being said, I can live with it if we determine that it's no big deal to keep driving it.

Thanks in advance for your time and typing.

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Last edited by Shunpiker; 02-05-2019 at 10:38 AM. Reason: punctuation
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Old 02-07-2019, 08:02 AM   #2
NASIOC Supporter
Member#: 132
Join Date: Jul 1999
Chapter/Region: Tri-State
Location: PA
2006 GT Ltd 5spd sdn
'15 WRX 6spd CWP, '02 WRX


Could be a lot of things, but purely based off your mileage and the fact that it seems to be "missing" in the cold weather, I'd say a weakening coil pack may be your culprit. Weak spark is exacerbated the colder it gets. In most cases, our coil packs begin to weaken over time, not just die at once. It will show up more when the engine is under load(i.e.-under boost, accelerating). As far as I know, there is no way to "test" a coil pack other then isolate what cylinder is missing, then swap the coil pack with a known good one, wait for the car to miss again, then see if the miss followed the suspected bad coil pack.

Be sure your spark plugs are in good condition and gapped correctly as well. Also, make sure the connectors for the coil packs do not have any corrosion on the pins inside.

Good luck!
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Old 02-08-2019, 11:48 AM   #3
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Member#: 206421
Join Date: Mar 2009
Location: Central NC
2003 wrx


Hi Shik,

Thanks for the feedback and info. I'll keep a closer eye on which cylinder is misfiring and research from there. I really appreciate your time.

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Old 02-13-2019, 04:22 PM   #4
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Join Date: Jan 2019

If you read the CEL with any OBD2 tool, the code will specify which cylinder is misfiring. I just went through this with my FOZ XT, was a coil pack and was also a flashing CEL, i think my code was P0304 where the 4 is the cyl number.
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Old 02-13-2019, 10:37 PM   #5
hybrid gti 2
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Location: (818) 300k+ ej205 ppg 5mt
02 vf30 pnp wagon
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Wiggle the harness for the coils and see if your idle changes
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Old 02-17-2019, 01:23 AM   #6
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Join Date: Feb 2019

If you havent done plugs In a while or have done them and didn't check the gap you may be blowing the spark out when coming on boost, I had this issue in my 00 forester turned out to be a 1mm gap instead of the required. 7mm gap, hope this helps!
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