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Mike V.
Mike V., Subaru Technician
Category: Subaru
Satisfied Customers: 25504
Experience:  Certified Subaru Technician, factory trained by Subaru.
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I want with you on my question about my Subaru WRX. I

Customer Question

Hi Mike, I want to follow up with you on my question about my Subaru WRX. I replaced the timing belt like you suggested but it didn't solve my problem with misfires on all four cylinders. Before we replaced the belt we checked the timing and it seemed to be spot on, however it was time to replace the belt. What would be causing all four cylinders to be misfiring and to only have compression of 50 PSI?
Submitted: 8 months ago.
Category: Subaru
Expert:  Mike V. replied 8 months ago.

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Expert:  Mike V. replied 8 months ago.

50 psi on a cylinder would explain a misfire, but only on that cylinder. It shouldn't affect all of the cylinders. With compression that low it's either a stuck valve. bent valve or broken compression ring on the piston.

It's an odd issue you are having, I think I would next check the fuel pressure, since it's affecting all the cylinders, however if you only have 50 psi on one of the cylinders, you have a bigger issue to contend with first to try and find out why.

Sometimes you can put some oil in the cylinder and retest compression. I know its a pain on this engine, but if the compression comes up with the oil, then the rings are the problem, if not, then it's a valve issue.

Customer: replied 8 months ago.
Just to clarify I have 50 PSI on all four cylinders, not just one.
Expert:  Mike V. replied 8 months ago.

Ok, I'm sorry, I didn't realize that.

All 4 like that is almost always timing, The only other thing I can think of would be worn out cams causing that or catastrophic failure of the belt which we know didn't happen. I suppose all the rings could have gone bad, but I have never heard of that. Surprised it will even run with compression that low. I think the min on this engine is about 120 psi

Expert:  Mike V. replied 8 months ago.

Please let me know if there is anything else I can do to help.
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Thanks so much!

Customer: replied 8 months ago.
I seem to be running out of options here fast! I may need to take it into a shop here soon. I've done quite a bit to chase down the problem but nothing seems to have helped. I've replace the mass air flow sensor, fuel filter, spark plugs, timing belt, crank shaft sensor, cleaned the cam shaft sensor, and replaced the O2 sensor. (I also had a P0171 code, the new O2 sensor fixed that problem). Could the turbo be affecting the compression in the cylinders? Maybe a vacuum hose or something has come loose?
Expert:  Mike V. replied 8 months ago.

Technically it shouldn't be affecting the compression. Because all the valves should close to build the compression and the engine isn't running when you check it.

I think the same for the vacuum hose, but, if there is a vacuum leak when it's running perhaps that's causing the misfires on all cylinders.

With it running spray some carb cleaner along the intake and the turbo and see if the idle smooths out. If it does, then you have a vacuum leak. It could also speed up.

Expert:  Mike V. replied 8 months ago.

Not saying you did the compression test wrong, but perhaps the tester has a problem. To get the exact same compression on each cylinder is pretty unheard of

Customer: replied 8 months ago.
when we did the compression test we also thought the gauge might be faulty, but my dad recently purchased it to work on his truck. All four cylinders averaged out to around 50 PSI during our testing. We can give the carb cleaner trick a try.
Expert:  Mike V. replied 8 months ago.

Seems like the next best step, but I am puzzled by that compression my friend.