09 Wrx running on 3 cylinders, compression is fine. What next?
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This is a discussion on 09 Wrx running on 3 cylinders, compression is fine. What next? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; I am having a bit of difficulty figuring out what is plaguing my car. I am running a 20g swapped ...

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    Registered User Ashesofthewake's Avatar
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    Question 09 Wrx running on 3 cylinders, compression is fine. What next?

    I am having a bit of difficulty figuring out what is plaguing my car. I am running a 20g swapped 09 WRX with full bolt ons and pushing 331hp/351tq at the wheels. Stock internals. The other day on my way to work the car started running rough intermittently. (low power, strong vibrations etc) It would happen for about 5 seconds then go away completely. I finally pulled over and got a tow home when it started running rough continuously. There was no CEL, however the roughness counter on cylinder 3 was counting rapidly up to 100 over and over again. Raw fuel smell from exhaust as well.

    The first thing I tried was swapping the coil packs to no effect. Car was still not really running on cylinder 3.

    I tested compression on cylinder 3 only and got 127 psi

    The plug looked fine, nice golden brown and and I tested the spark with the plug out of the car and it appeared strong.

    I am a little stumped. Cylinder 3 obviously seems to be getting fuel as I can smell raw fuel in the exhaust, and my coil packs are fine and there is a strong spark. Any ideas what I should look at next?

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    He simply abides. SD_GR's Avatar
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    09 Wrx running on 3 cylinders, compression is fine. What next?

    It may not be getting all that at once I guess. I'd be tempted to swap injectors. If the problem doesn't move to another cyl I'd suspect wiring.
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    Registered User UEDan's Avatar
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    Do another compression test, and with the rest of the cylinders as well. What are they getting?
    Then do a leakdown test.
    My car did that almost exactly when I had a slightly burnt valve causing bad compression.

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    He simply abides. SD_GR's Avatar
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    I'm betting the others will be similar and hoping compression is ok for the OP.
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    Registered User Ashesofthewake's Avatar
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    Quote Originally Posted by SD_GR View Post
    I'm betting the others will be similar and hoping compression is ok for the OP.
    Me too.

    I'll start by finishing the compression test. I know 127psi isn't optimal but the car does have 72K miles on it. In my head anyway I couldn't see 127psi causing it to not run at all on that cylinder, but I could be completely off base.

    If my numbers are all around that area I'll swap injectors and see if that makes a difference , but they are pretty new ID1000s.

    Thanks for the suggestions guys, if it turns out to be valves or piston related I suppose I have an engine build in my near future.

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