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Compression ~130. What's coming in the future?


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Back in July I had a misfire that was eventually diagnosed as a bad coil pack. As part of their diagnosis they did a compression test on 3 cylinders (they couldn't remove plug #2). They didn't record the actual readings but the service manager said they were about 130. I wasn't surprised by this as my UOA's have shown some fuel dilution. Today I had a second coil pack replaced due to misfires and CEL. The car has just over 164,000 miles on it and I want to keep it as long as possible. It spent all of its life in SE PA until I bought it in 2010 so the body and undercarriage are in pretty good condition. For various reasons I still haven't re-tuned since installing the 16g and sti UP in February so am still running with the BCS tubing disconnected so I am boosting to only waste gate pressure.

 

With these givens, what should I expect and how far off might it be? I'm assuming it would be a bad idea to attempt to do the tune until the compression issue is fixed. What are some of the options I might have for correcting this?

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Compression numbers per the FSM are 142-171 psi, difference between cylinders is 7 psi or less. That is @ 350 rpm (using the starter motor to crank it) with the throttle WFO and all 4 spark plugs out (which the shop did not do if they couldn't remove the #2 plug).

 

Hence, 10% difference is too much per the FSM, but those are very tight tolerances.

 

If they are all at 130ish and within maybe 10 psi, I'd say yeah it's just an old motor that is a little tired.

 

Why couldn't they remove the #2 plug??? PB Blaster soak it when it's warm, sounds like the threads are seizing up in there or something. Fail. Supposed to use anti-seize somewhat liberally for 100K iridiums like the LGT uses.

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In terms of getting a tune, I probably wouldn't worry too much about the compression #'s, -assuming- that the untested cylinder would post similar #'s to the other cylinders that were tested.

 

Definitely agree that some datalogging (part throttle as well as WOT) & pulling a learning view would be useful to see where things are at. Lately I've been datalogging every time I drive, just to keep tabs on things and to get a comfort level that the car is running well.

 

I had a compression & leak-down test done on my recently-acquired '05 OBXT, @ Procom Racing in Tom's River NJ. Tests were done on a warm motor. I believe the block is the original one w/ ~150k mi, and as of a year or so ago it has Wiseco forged pistons, Manley Turbo Tuff I-beam rods, ACL bearings, SuperTech valves, VF52, Perrin TMIC, GrimmSpeed EBCS, plus a bunch of other stuff that were in place when I bought it.

 

Compression came in at a disappointing/disconcerting 120 on cyls 1, 2 and 4. #3 came in at 110. Leakdown was 10% on cyls 1, 2, and 4. #3 came in at 13%. Lou @ Procom indicated that it's probably b/c of the rings, not the valves.

 

I'm not seeing anything worth mentioning out the tailpipe @ WOT/high RPM (wife drove behind my car to confirm), and oil consumption doesn't seem too bad (~1/2 to 2/3 qt b/n ~4k mi oil changes with a -lot- of WOT, 2500-6200+ RPM datalogging blasts in between, Rotella 5W40 oil, OEM Subaru oil filter).

 

On Procom's Mustang AWD 500 SE dyno (w/ a protune by Lou the same day the compression/leak down tests were done), it put down 303 whp / 339 wtq in mid-70F ambient temps, and is nice and smooth part throttle/WOT.

 

I'll be keeping an eye on the oil consumption & will be doing compression/leak down tests periodically to monitor things, but the motor seems pretty happy despite the lowish compression and higher than optimal leak down #'s.

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I agree, 130 is not that bad.

 

Why couldn't they remove #2 plug ?

They said it was stuck. I think this was the first plug I replaced of the 4 and I seem to recall after struggling to get it in and started I realized I had forgotten the never-seize and decided to not pull it and start over again. I have a suspicion that they may have not sprayed it. Regardless they decided that a stuck functioning plug was better than breaking it off and causing bigger problems.

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Sounds like you may have cross-threaded the spark plug, so.... it may be smarter to just leave it alone and just fix it when you inevitably will have to pull the motor, or if something else forces your hand.

 

130 isn't terrible, and the fact that the shop didn't record the numbers leads me to believe they were doing a quickie job and weren't really on the ball. Why go through the time to do a compression test if you aren't going to log the numbers? Amateurs.

 

So, you probably just want to get a decent tune and be on your way.

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If you plan to keep the car, start saving your money and do a rebuild next spring.

 

I think you saw my thread from last year, "got some new stuff for engine R&R"

 

Plan ahead and things work much better.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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The compression when I bought my outback earlier this year was at 125psi on all four cylinders--it was within 1psi for every cylinder.

 

Not too worried about it, but nonetheless I'm with Max--plan ahead and things become a bit easier. I have a spare block in the garage and hope to build it (or at least start on it) over the winter. Will stash it on the shelf for future use if needed. Although that type of thing isn't for everyone, I like it--and if I decide I don't need it I'll just pass it one for whatever I have into it.

"Bullet-proof" your OEM TMIC! <<Buy your kit here>>

 

Not currently in stock :(

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The delta as others have said is the more important number. 130 isn't terrible.

 

As others have said keep an eye on it and begin preparing for a rebuild at some point, but I don't think it's immanent.

 

I would have it tuned and setup correctly so that the turbo is working properly etc.

 

-Mike Paisan

 

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Sounds like you may have cross-threaded the spark plug, so.... it may be smarter to just leave it alone and just fix it when you inevitably will have to pull the motor, or if something else forces your hand.

It's possible but I used only my hand to turn the socket to get it started for a few turns. I don't think I applied enough force to get it cross-threaded.

 

130 isn't terrible, and the fact that the shop didn't record the numbers leads me to believe they were doing a quickie job and weren't really on the ball. Why go through the time to do a compression test if you aren't going to log the numbers? Amateurs.

In the end when the problem turned out to be a bad coil pack I wondered if they had a green tech working on it. I would have expected them to swap the coil packs first. I was glad to have the compression test done but I think once they ruled that out as contributing to the misfire they just put it back together and moved on to other possibilities.

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The compression when I bought my outback earlier this year was at 125psi on all four cylinders--it was within 1psi for every cylinder.

 

Since most meters are measuring in units of god knows what it's more important that they are similar than the actual numbers.

 

125psi on one meter may be 150 on another on the same engine.

 

Just go ahead and make a tune. If the engine runs good as it is now without any knocking or other bad habits it should be fine.

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It's possible but I used only my hand to turn the socket to get it started for a few turns. I don't think I applied enough force to get it cross-threaded.

 

 

In the end when the problem turned out to be a bad coil pack I wondered if they had a green tech working on it. I would have expected them to swap the coil packs first. I was glad to have the compression test done but I think once they ruled that out as contributing to the misfire they just put it back together and moved on to other possibilities.

 

Yeah we follow a heirarchy on misfires to rule out the simple things first like plugs, coils, wiring, etc. On the LGTs we've seen quite a few single cylinder misfires coming in over the past year or 2 and 95% of them were bad coil packs or coil pack connectors.

 

-Mike Paisan

 

http://www.pbase.com/paisan/image/91072632.jpg http://www.pbase.com/paisan/image/145749898/original.jpg http://www.pbase.com/paisan/image/133406601.jpg http://www.whiteline.com.au/images/logos/perf1.jpg

11+ Years Maintaining, Modifying and Educating TriState Subaru Enthusiasts.

Like us on Facebook! | E-mail: sales@azpinstalls.com | 725 Fairfield Ave | Kenilworth, NJ 07033 | 908.248.AZP1 (2971) |AIM: AZP Installs

"Race Tested, Enthusiast Approved!"

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