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Old 02-04-2018, 07:45 PM   #1
Scooby Newbie
Member#: 481638
Join Date: Feb 2018
Default EJ20 Low Compression On Cylinder 4?

Hey everyone, this is my first post on this website!

Hereís my situation:

I have a 2003 WRX sedan with the EJ20 with the V3 Accessport and a Stage 2 tune. Car has a full TurboXS catless turbo-back and an SPT Intake.

Bought the car two months ago and drove it 2 hours home with no problems, the car felt great actually. Two weeks ago or so, I got a CEL for Evap System leak. After finding a disconnected hose near the Purge Solenoid, I reset the ECU to get rid of the code. I let the car idle for 10 mins then took it for a drive to let the car see boost.

Shortly after, I got a CEL but this time it was flashing. I read the codes with the Accessport and it showed a misfire in Cylinder 4. After replacing all the spark plugs, I reset the ECU, let the car idle for 10 mins, took the car for a drive, and when I checked the CEL codes again, it showed a misfire on all 4 cylinders.

The thing is, the car idles fine, runs fine, boosts fine, drives fine, there are no weird noises and the car doesnt really burn oil.

In the next couple days, when I would read the codes, it would say either cylinder 1-4 or 2 and 4 or 1 and 3 or any combination of those. The misfires would bounce around from Cylinder to Cylinder, yet the car would still idle the same as always.

I finally did a dry compression test and found this:
Cylinder 1: 150psi
Cylinder 2: 160psi
Cylinder 3: 155psi
Cylinder 4: 30psi

Yes thatís right, 30psi. Yet the car runs and drives flawlessly.
Iíve put on a stock Intake, Iíve tested to make sure the fuel filter isnt clogged (itís not), Iíve replaced the spark plugs, Iíve cleaned the MAF, Iíve put in a different clean MAF from my brotherís EJ20, Iíve swapped coil packs, but all of it leads to the same thing. A misfire on one or two cylinders.

I feel that if it truly was a misfire on two cylinders, the car would idle or rev as smoothly as it does currently. Iíll try and post a video later.

Anyone have any ideas?? Leakdown test is the next thing for me to check out.
Thanks in advance.
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Old 02-07-2018, 02:07 PM   #2
Scooby Newbie
Member#: 481638
Join Date: Feb 2018


Today, I was checking the MAF sensor when I noticed that the coupler that connects the turbo inlet pipe to the turbo itself was 100% loose. I shoved it onto the turbo and tightened that thing down tight.

My thoughts are:
Could this have basically created a giant vacuum leak which caused a lean condition in cylinder 4? If so, what would the culprit be? Valves? Piston rings? please let me know!
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Old 02-08-2018, 09:43 AM   #3
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No one has any suggestions??
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Old 02-08-2018, 10:32 AM   #4
Scooby Newbie
Member#: 472037
Join Date: Jul 2017
Chapter/Region: MWSOC
2018 WRX Limited


Are you still getting the same codes?
Could it be a failing fuel pump?
Does it only happen under WOT or all the time?
If you say drive gently for a while after clearing the code, does it still happen?
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Old 02-08-2018, 10:36 AM   #5
Scooby Specialist
Member#: 40453
Join Date: Jul 2003
Chapter/Region: South East
Location: Metairie, Louisiana

It would definately cause it to run lean as out would be sucking in unmetered air but it would not cause a vacuum leak. If you had 30 psi on one cylinder and it still ran fine I would repeat the test to verify that it was correct. If I got the same results I would start planning on a new shortblock.
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Old 02-13-2018, 10:54 PM   #6
Crispy 1
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Member#: 478948
Join Date: Dec 2017
Chapter/Region: South East
Location: Hendersonville, NC
02' WRX


I've had basically the same problem except mine only gets the misfire after a warm start and only at idle. I've gotten the p0171 and p0301/p0303.

I've done everything you have along with a smoke test cleaned the IACV and replaced the gasket, cleaned cam and crank position sensors and reset my spark plug gaps recently done by a local Subaru shop that changed them and the driver side valve cover gasket.

I haven't done a compression test yet.

They left off a pcv hose and the plugs we're set to about .046-.048 so although pissed I was excited to see that, thinking it would fix my issue. I set them to .28 and started the car. Let it idle a few minutes and took it for a drive. Car felt a little better and idled slightly better. Cut it off ran in the house for 5 minutes and restarted it to only miss and barely idle a lot worse than before.

After about 10-20 seconds it smoothed out. This time of badly idling is the same time the original fuel pump (150,000 mi.)runs at 100%. I'm starting to lean toward a tired or dying fuel pump or pressure regulator. Gonna test pressures asap.

Anyways sorry to make such a long post in your thread I just thought it might help us both. Good luck and please let us know if you get it fixed or the compression test could be in accurate.
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Old 02-14-2018, 10:10 AM   #7
Samurai Jack
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Join Date: Jul 2002
Chapter/Region: NESIC
Location: Not in my own time
2002 Enemy of Aku


Originally Posted by Rickyh View Post
If you had 30 psi on one cylinder and it still ran fine I would repeat the test to verify that it was correct.
Re-check all your hose connections and then, as stated above, re-do the compression test.

Do a dry test first and then do a wet test.

If the compression stays low from both the dry and wet test, could be a valve issue ( valves, valve seals, etc. ) or a ring/piston issue

If the compression improves when doing the wet test, then probably a ring/piston issue.
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