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Old 03-06-2017, 08:13 PM   #1
rick_740
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Default 2011 WRX low compression

MAF sensor code and misfire code on cyl 2 and 4, installed new plugs and rotated coils from side to side. Misfires stayed on 2 & 4. Checked compression and all 4 cylinders checked 70psi, done leak test and all were equal at approximately 7%. Timing belt appears to in time. Could the hydraulic timing on the intake cams be messing up?
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Old 03-07-2017, 12:24 PM   #2
Charlie-III
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Chapter/Region: Tri-State
Location: USA, North NJ, 07456
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1998 Legacy 2.5GT
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Was the battery fully charged?
Was the throttle fully open?
Did you follow up with a "wet test"?

I will assume all 4 are 70PSI? That sounds really low, do you have a book value?
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Old 03-07-2017, 01:30 PM   #3
rick_740
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battery was fully charged,thrittle wide open, engine cold, no wet test, book says 147-171, all 4 were even.
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Old 03-08-2017, 07:08 PM   #4
Elbert Bass
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You should have a cam correlation or fault code with a stuck/faulty cam sprocket.

Exactly which MAF code?
Any driveability symptoms?
Any service or repairs performed immediately before codes?
Have you followed up with a wet compression test?
Looked for damaged/chewed wires on bank 2 injectors (drivers side head) or wiring harness?

First thing I question is the compression results - that by itself could indicate the engine is timed incorrectly (unless you got a faulty gauge). I would double check that to be absolutely sure - appears leaves room for error. I go as far as using a short straight-edge or screwdriver and a mirror to verify cam timing in-chassis.
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Old 03-09-2017, 09:38 AM   #5
Charlie-III
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1998 Legacy 2.5GT
Silver Sleeper Wagon

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Agreed, engine in the car (especially a DOHC) I use a small (2" x 3") mirror to check cam timing marks to cover marks, this gets you a "direct head on view" with NO parallax. Then, using the crank bolt, spin the engine 2 revolutions or multiples thereof and recheck.

When doing a compression test, first is "dry" second is "wet" (using a few ounces of oil) to see numbers. If the numbers come up, it gives an indication of ring wear since the oil helps seal the rings a bit better.

I also crank long enough to get 4 or more compression strokes on a cylinder, you want to capture the max value from the cylinder.
Throttle fully open raises the value for a more accurate number.
Fully charged battery gets enough RPM to limit losses due to valve overlap.
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