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Old 11-05-2004, 07:14 PM   #1
serendipity
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Default Does this sound like a hosed piston to you guys?

I'll get a compression test done soon. In the meantime, do these symptoms ring any bells?

At idle, the car feels slightly funky - almost like a miss, but different. Driving slowly is the same - basically normal, but if you pay attention, something just feels "off". But when I get on the gas and start to build some boost (couple psi), the engine tone suddenly changes, and the car seems to stutter. It has little power at this point (though obviously I haven't pushed it - just 50% throttle till it starts happening).

This started happening suddenly while I was dialing in boost last weekend. I was on a WOT run, at about 20psi (car was tuned for 22psi, I'd been running 20psi most of the time, and no detonation). There was no knock event (I was logging at the time), AFRs were fine, but the car kinda bucked and lost power. Ever since, it's exhibited the behavior described above.

I replaced plugs (what a headache - only took 45 minutes to swap them, but NOBODY has plugs in stock. All the dealers would have had to special order them), since they were due to be replaced anyway. Exactly the same behavior after the plugs were replaced.

So, I'm ready for the worst, but what do you folks think? Oil seems fine (no coolant or strong gas smell). Coolant seems fine (it's green, not gassy or oily). No noticeable plumes of smoke from the exhaust.
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Old 11-05-2004, 07:19 PM   #2
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You've checked for boost leaks?
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Old 11-05-2004, 07:37 PM   #3
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Quote:
Originally Posted by maestro
You've checked for boost leaks?
Yeah. AFRs stay OK. Hoses and everything seem to be tight.
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Old 11-05-2004, 11:20 PM   #4
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tried resetting the ECU?
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Old 11-05-2004, 11:28 PM   #5
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Quote:
Originally Posted by John Sever
tried resetting the ECU?
Yes. Had the battery disconnected while changing plugs. Same behavior afterwards.

Oil smells pretty gasoliney now. So I'm pretty sure it's not good news
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Old 11-05-2004, 11:35 PM   #6
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A telltale sign of low compression is when you start the car..... when the car cranks it doesnt sound steady and uniform...... hard to explain on a computer but its definately a distnct sound at startup.

The easiest way I would describe it is "erratic cranking" if that makes sense to you.
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Old 11-06-2004, 12:07 AM   #7
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Quote:
Originally Posted by carguyx
A telltale sign of low compression is when you start the car..... when the car cranks it doesnt sound steady and uniform...... hard to explain on a computer but its definately a distnct sound at startup.

The easiest way I would describe it is "erratic cranking" if that makes sense to you.

I'd have to go start it again to double check, but that sounds pretty close.
It sounds kinda lopey or something. Even at idle just after starting, it sounds similar to a miss (as though a coil pack were disconnected), but different.

I'll have the compression gauge tomorrow and post results. I'm expecting at least a piston (ring/ring land), and just hoping it didn't score the cylinder wall...
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Old 11-06-2004, 12:13 AM   #8
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try pulling the crank case vent hose while the car is running, if you get smoke, ya prolly blew a ring land
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Old 11-06-2004, 12:16 AM   #9
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when you crank it, if you have a miss, it's a ring or land.

da-da-da-de-da-da

Jorge (RiftsWRX)
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Old 11-06-2004, 08:50 PM   #10
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That sounds like what happened to my 02... it ended up being a clogged Cat. I ended up replacing my Downpipe and 3rd Cat to fix it.
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Old 11-07-2004, 12:00 AM   #11
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Quote:
Originally Posted by caryfd227
That sounds like what happened to my 02... it ended up being a clogged Cat. I ended up replacing my Downpipe and 3rd Cat to fix it.

No cats here
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Old 11-07-2004, 01:27 AM   #12
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And the verdict is?
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Old 11-07-2004, 08:33 AM   #13
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Still haven't gotten my hands on a compression tester. Hopefully I can borrow a friends this morning and find out.
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Old 11-07-2004, 11:58 AM   #14
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Bizarre. Just bought a compression tester and tested each cylinder. Basically 120psi across the board. The cylinder in the front on the driver's side was about 115psi. Passenger side back was 118psi. The other two were 120psi dead on.

What have others found the stock STi block to hold? I thought I remembered others saying around 120psi.

Now I'm just confused. It does sound kind of like an air leak that "blows open" at high pressure, but why would my air/fuel ratios stay "normal"? It should dive even richer if it's losing air...

Anyone have any ideas on what to check next?
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Old 11-07-2004, 01:28 PM   #15
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Quote:
Originally Posted by serendipity
Bizarre. Just bought a compression tester and tested each cylinder. Basically 120psi across the board. The cylinder in the front on the driver's side was about 115psi. Passenger side back was 118psi. The other two were 120psi dead on.

What have others found the stock STi block to hold? I thought I remembered others saying around 120psi.

Now I'm just confused. It does sound kind of like an air leak that "blows open" at high pressure, but why would my air/fuel ratios stay "normal"? It should dive even richer if it's losing air...

Anyone have any ideas on what to check next?
Do you have a boost guage in the car?
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Old 11-07-2004, 01:54 PM   #16
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Quote:
Originally Posted by carguyx
Do you have a boost guage in the car?
Yes, and a carputer on which I constantly log from my UTEC and Tuna.

Boost and AFR seems fine, which is why, although it almost sounds like an air leak, I'm skeptical. I don't, for example, get low boost, high MAF, and super-rich air/fuels...

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Old 11-07-2004, 03:38 PM   #17
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What confuses me is the normal AFR, based on O2 sensor readings, because it should pick up a clogged injector, bad injector, bad plug wire and bad coil pack, all of which can do this (and has done this on my old 2000 RST which acted like yours when it happened). YOU ALREADY VERIFIED THE PLUGS ARE FINE, which means no det, in agreement with your loggings.

If you had a boost leak after the MAF I'd expect a drop in boost and rich AFR. If you had a clogged fuel filter I'd expect lean AFR.

Compression is good, but what about a leakdown test? What about water in the gas?
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Old 11-07-2004, 04:15 PM   #18
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Quote:
Originally Posted by ImprezaRS dot com
What confuses me is the normal AFR, based on O2 sensor readings, because it should pick up a clogged injector, bad injector, bad plug wire and bad coil pack, all of which can do this (and has done this on my old 2000 RST which acted like yours when it happened). YOU ALREADY VERIFIED THE PLUGS ARE FINE, which means no det, in agreement with your loggings.

If you had a boost leak after the MAF I'd expect a drop in boost and rich AFR. If you had a clogged fuel filter I'd expect lean AFR.

Compression is good, but what about a leakdown test? What about water in the gas?
No leakdown test yet. Almost certain it's not the gas, because I was halfway through a tank when it happened. I mean, it is almost consistent with a hose that's blown off or maybe a bad injector that finally went south.

One other data point I just realized is missing from above. After a "stutter event", if I let it stutter for more than about .5 seconds, the CEL will flash indicating misfires (again, UTEC knock count stays at 0), but no code is stored and the CEL doesn't actually illuminate. So to clarify the timeline, it's give it ~50% throttle till it makes a couple psi, car will stutter while gas is held down, let off gas, and after about 3-4 seconds, CEL will flash a handful of times.

This apparent misfire is why I was convinced it was either plugs or a piston. When I took the new plugs out to do the compression test today, all 4 plugs showed the same condition, so I would have thought I could rule out plug wires, coil packs, etc. None was more or differently fouled than the others. (Same for the original plugs that I took out Friday - none was worse than any others. All just had the usual discoloration for a healthy used plug)

One more question for you ImprezaRS - how rich did your AFRs go with (I'm assuming) one non-firing cylinder?

Thanks for your help guys. I'm stumped.
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Old 11-07-2004, 05:07 PM   #19
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More inconclusive info. I took the intercooler off to double check some more hoses and stuff. The throttle body makes a "whirring" noise that I don't remember hearing before (but it would have been much quieter with the intercooler on there). I checked the range and it still opens all the way and seems to be working fine. So I think this is nothing.

Also checked spark by putting a plug in each coil pack and verifying it was sparking - no problems with spark.

Now I'm wondering if I have an injector that's dieing. I'm running perrin modified stockers. Anyone know of a method to test them? I think I have access to my stock injectors (a buddy bought them but hasn't installed them), so I guess I could always swap back just to see if that's what's causing my problem.
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Old 11-07-2004, 05:46 PM   #20
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Quote:
Originally Posted by serendipity
More inconclusive info. I took the intercooler off to double check some more hoses and stuff. The throttle body makes a "whirring" noise that I don't remember hearing before (but it would have been much quieter with the intercooler on there). I checked the range and it still opens all the way and seems to be working fine. So I think this is nothing.

Also checked spark by putting a plug in each coil pack and verifying it was sparking - no problems with spark.

Now I'm wondering if I have an injector that's dieing. I'm running perrin modified stockers. Anyone know of a method to test them? I think I have access to my stock injectors (a buddy bought them but hasn't installed them), so I guess I could always swap back just to see if that's what's causing my problem.
The noise from the throttle is normal.
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Old 11-07-2004, 10:23 PM   #21
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This might be something worth trying, replace the front O2 sensor(one on manifold). They have been known to go bad out of the blue and cause similar symptoms that you are seeing. Worth a try?
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Old 11-07-2004, 11:04 PM   #22
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Quote:
Originally Posted by dsmperformance
This might be something worth trying, replace the front O2 sensor(one on manifold). They have been known to go bad out of the blue and cause similar symptoms that you are seeing. Worth a try?

I guess it's possible that the sensor went south, but I really doubt it has anything to do with my problem. First, at idle, in closed loop fueling, AFRs stay right at 14.7, according to my wideband. And second, when the problem happens, it's at greater than 25% throttle, which means the UTEC is running fueling, in open-loop, without any regard for the O2 sensor.
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Old 11-08-2004, 01:34 PM   #23
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Bump for the afternoon crowd? Any ideas? I'm kinda lost here - was convinced it was spark or piston...
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Old 11-09-2004, 06:40 AM   #24
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i have stock injectors laying around...

...if you want to try them out, you can just send me money for shipping...and then if you end up needing them, you can send me the rest of the money, or else you can send them back?
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Old 11-10-2004, 12:35 AM   #25
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Quote:
Originally Posted by serendipity
No leakdown test yet. Almost certain it's not the gas, because I was halfway through a tank when it happened. I mean, it is almost consistent with a hose that's blown off or maybe a bad injector that finally went south.

One other data point I just realized is missing from above. After a "stutter event", if I let it stutter for more than about .5 seconds, the CEL will flash indicating misfires (again, UTEC knock count stays at 0), but no code is stored and the CEL doesn't actually illuminate. So to clarify the timeline, it's give it ~50% throttle till it makes a couple psi, car will stutter while gas is held down, let off gas, and after about 3-4 seconds, CEL will flash a handful of times.

This apparent misfire is why I was convinced it was either plugs or a piston. When I took the new plugs out to do the compression test today, all 4 plugs showed the same condition, so I would have thought I could rule out plug wires, coil packs, etc. None was more or differently fouled than the others. (Same for the original plugs that I took out Friday - none was worse than any others. All just had the usual discoloration for a healthy used plug)

One more question for you ImprezaRS - how rich did your AFRs go with (I'm assuming) one non-firing cylinder?

Thanks for your help guys. I'm stumped.
I used a Autometer AFR so it didn't give me numbers like 11:1 - it would switch from Stoich to rich at about 2 o'clock. It just went to past 3 o'clock on the rich, and my EGT would drop to below 1100 F. I leaned it out so much thinking it was a tuning problem that I cooked #4 cylinder. Turned out all the fuel from unburned #3 with the bad plug wire was being picked up by the EGT probe on #3 and the O2 sensor in the up-pipe that I leaned out #4 too much in my effort to fix it. Just shows why you should measure EGT on more than one cylinder, eh?
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