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Old 01-18-2013, 09:22 PM   #1
thomasm55
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Unhappy No power under load. Bad gas?

Hey guys,

I have been stuck with this problem for over a month now. I have an 06 STi (pretty much bone stock). I installed a short ram intake 2 weeks before this happened. One day I randomly start the car and I have no power whatsoever and idle is a bit rough. When I press the throttle I can hear a "burping" or backfiring sort of sound from the intake. The engine has a strong hesitation and I have troubles reving it past 3000rpm. I have no CEL and nothing had come up in the past. I took off my entire intake system including the turbo inlet and all the hoses are fine. Inspected the inter cooler as well.

I replaced the MAF with a known working one and no difference.
I put the stock air box on and reset the ecu and still no luck.

Any ideas?
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Old 01-19-2013, 03:44 AM   #2
BlackFighter
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With a short ram you would have needed a tune for that. If you have not tuned for the short ram, you might have blown a ringland, maybe. Take the oil fill cap off while the car is running and see if any exhaust gasses are comming out of there.
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Old 01-19-2013, 08:29 AM   #3
cineris
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Yeahhhh I hope you tuned it.
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Old 01-19-2013, 11:00 AM   #4
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Man that sucks... hate to tell u but its not bad gas.

Compression test asap and leak down test. Probl. A blown ringland like stated.

Try not to drive it as that may cause more damage making the repair more $$$$ .
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Old 01-19-2013, 07:46 PM   #5
thomasm55
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I took off the oil cap and no smoke (at start and while reving). I looked at the exhaust gas and no sign of blue smoke either.
The car idles smoothly but then drops to like 100 rpm for about 5 sec and then rev's back up as if the ecu is compensating the fuel ratio. When the rpm's drop that low is only shaky then. Is it possible that it might be an o2 sensor?

I cant see it being the rings if this problem happened overnight. Car ran strong the whole time. Im gonna run the compression test, and leak down test on monday and let you guys know whats up.
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Old 01-19-2013, 08:00 PM   #6
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Do a compression test and report back
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Old 01-20-2013, 01:00 AM   #7
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Also, are you tuned for that intake?
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Old 01-20-2013, 11:17 AM   #8
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Quote:
Originally Posted by Half Crazed View Post
Also, are you tuned for that intake?
He said he put the stock intake back on and no change was observed.

OP have you checked for boost leaks? Or pre turbo but post maf leaks?
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Old 01-20-2013, 12:05 PM   #9
bboylocob
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Just do a compression test
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Old 01-20-2013, 01:44 PM   #10
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Dirty MAF.
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Old 01-20-2013, 03:58 PM   #11
thomasm55
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Dirty MAF.

Cleaning it was the first thing I did before swapping it with a working one.
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Old 01-20-2013, 04:12 PM   #12
jwsuba
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Default the wires brake right by the battery for the engine harness

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Old 01-22-2013, 12:19 AM   #13
thomasm55
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I did a compression test today and all cylinders are almost spot on to 105psi (I did not warm engine prior to testing). Spark plugs looked fine as well as the coils.

Plugged a timing light in and the value at idle was 7 degrees and then jumped to 18 degrees when the engine started to bog down. Do you guys think it may be a failed crankshaft position sensor?
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Old 01-22-2013, 12:32 AM   #14
Half Crazed
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I don't think your car would start if it's a failing crankshaft position sensor.. that and a CEL.

I wonder if it's a bad knock sensor? Do you have an access port and are able to log? Sounds like it might be pulling a ton of timing..
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Old 01-22-2013, 12:33 AM   #15
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also, what about other throttle positions - like 1/4 or 1/2 throttle? any bogging?
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Old 01-22-2013, 12:36 AM   #16
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could also be fuel pressure.. either from pump or regulator. just throwing ideas out there at this point since you checked air, spark, and compression..
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Old 01-22-2013, 01:32 AM   #17
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ive had this problem before i had a dead coil check the packs
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Old 01-22-2013, 08:52 AM   #18
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The timing jumping up when the revs drop at idle is normal the car is trying to maintain the idle rpm. 105 compression is pretty low, but it was even so it could have just been the testing method (ie closed throttle plate instead of open) or the tester (really long hose, inaccurate gauge, etc). It might be an intermittent bad coil pack but this is so hard to diagnose without data from the ecu.
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Old 02-02-2013, 10:08 PM   #19
thomasm55
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Problem fixed! It was a stuck valve in cylinder #4. Had to replace the shims
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Old 02-02-2013, 10:34 PM   #20
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Quote:
Originally Posted by thomasm55 View Post
Problem fixed! It was a stuck valve in cylinder #4. Had to replace the shims

Was it misfiring i thought with a stuck valve it would misfire ?
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Old 02-25-2013, 09:36 AM   #21
Subaru5150
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Quote:
Originally Posted by Half Crazed View Post
I don't think your car would start if it's a failing crankshaft position sensor.. that and a CEL.

I wonder if it's a bad knock sensor? Do you have an access port and are able to log? Sounds like it might be pulling a ton of timing..
Ecu logic dictates that if the cam signal is not seen on start up the car will not start the first crank but will ignore the bad cam sensor and start the second crank with a CEL for a cam sensor. (on sti's ur avcs will be deactivated also)
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