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Old 12-05-2005, 11:00 PM   #1
InsatiableAmos
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Default Bad Hesitation and possible o2 sensor issues...

My '00 RS is at 51k miles right now, and just out of warranty (but still bone-stock). Around the high-30k miles mark i had huge hesitation issues and intermittent loss of power w/ a check engine light. Turns out i had a bad o2 sensor (and the ECU read it as a misfire...). I went through three o2 sensors (replaced at SOA's cost) and a few ECU reflashes before the car ran well again, but now (about 2 years later) i'm starting to get more and more serious hesitation immediately after a shift. It goes like this:

Accelerate to 4k-ish in first, let off gas and put clutch in simultaneously...shift. Gas the engine just slightly before letting off clutch, and the car just dies for a good second; feels like i stabbed the brakes or i hit the redline fuel cutoff (impossible, by this time it's back down around 3k rpm). Finally, the engine catches suddenly, and accelerates like normal. It'll occasionally happen at other rpms, but this is where i notice it most when driving hard.

The hesitation happens worst when i'm driving hard (making it even more disconcerting), but still occasionally occurs when driving lightly/commuting. I have no mods, and an almost dead clutch (being replaced/upgraded next weekend). This car has seen almost exclusively city driving for most of it's life...so shifting is important!

I'd like to get to the bottom of this issue so that i don't burn through a slew of o2 sensors on my OWN money, only to have the problem surface again later on.

Is it running too rich and drowning out the spark? Is the injector duty not ramping up fast enough for my foot and there's no fuel for the first second? Observation would lean towards my car running rich: carbonized exhaust tip, and terrible mileage (16-18mpg daily in mostly city), but PLEASE suggest anything. Only fix i've been contemplating is gettin an ECU reflash from i-speed because it seems to lean things out a little bit...

Help!
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Last edited by InsatiableAmos; 12-06-2005 at 02:19 PM.
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Old 12-06-2005, 08:35 PM   #2
InsatiableAmos
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I know someone here has to have an idea...
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Old 12-06-2005, 09:26 PM   #3
Ill.Subaru
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silva

Question Weird

Whats strange about that is your car could actually be dying out for a second and then when you re engage the clutch it could be "push starting" it. does it die out if you dont shift up? though it does sound like your running Turbo injectors without the turbo to eat the gas. Post your solution if and when you find it!!!
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Old 12-06-2005, 10:25 PM   #4
InsatiableAmos
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It doesn't give the hesitation unless i really get on the gas during the shift, though next time i'll try it without re-engaging the clutch to see what happens.

That's a real interesting thought you have though, any way i could check to see if i'm running stock injectors/fuel pump?

I suppose this car could've been turbo'ed before i bought it...
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Old 12-07-2005, 02:03 AM   #5
Kawikid20o2
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let us know what color injectors you have.
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Old 12-08-2005, 12:12 AM   #6
InsatiableAmos
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...not totally sure how to do that, but i'll get on it once these pesky finals are outta the way

Clutch and flywheel first, this sunday.
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Old 12-08-2005, 12:53 AM   #7
Kawikid20o2
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all you have to do is unplug the connector to the injector, and it will be most likely red unless you have upgraded injectors, or im an idiot.
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Old 12-10-2005, 07:12 PM   #8
InsatiableAmos
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If i'm not mistaken, i didn't even need to pull anything out/apart to see the injector color... They're the small black posts sticking diagonally out of the intake manifold just before it connects to the cylinder head, right?

Anyways, they're grayish black, and have a code written on them as follows:

FBLC100
000 9730

Hope that helps. Another odd note: the skip when i shift is MORE common on 87 octane fuel, but the car feels faster once it's going. I don't notice any serious knocking, but i'm not sure i've EVER heard serious knock...so maybe i just don't know what it sounds like. It still happens on 91+ octane occasionally though...
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Old 12-11-2005, 07:08 PM   #9
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New clutch and flywheel make it much smoother...but still rears it's (ugly) head on occasion. Any ideas?
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Old 12-12-2005, 10:40 AM   #10
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New development... If i stomp hard while in gear, it feels like it misfires once or twice (similar to the hesitation) before it'll start accelerating constantly. No backfires, no CEL's yet.

I also noticed my midpipe resonator is coming off at the seam, a potential trouble-causer?
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Old 12-12-2005, 10:43 AM   #11
Pat L.I.
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Quote:
Originally Posted by InsatiableAmos
New development... If i stomp hard while in gear, it feels like it misfires once or twice (similar to the hesitation) before it'll start accelerating constantly. No backfires, no CEL's yet.

I also noticed my midpipe resonator is coming off at the seam, a potential trouble-causer?
my car is doing exactly this. as well as feeling down on power / bogging.
just replaced the coil pack and cat two weeks ago, didnt fix anything. Car is going back to the shop on the 20th.

i doubt that an exhaust leak would cause a stutter like that.
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Old 12-12-2005, 03:03 PM   #12
InsatiableAmos
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Some guys over at rs25.com suggested trying new plugs and/or new wires...

Pat: if you get around to this or find something that works, please let ME know as well!

In the meantime i'll be scrounging around for a good price on this stuff.
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Old 12-12-2005, 03:28 PM   #13
Pat L.I.
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yeah ive done wires, plugs, coil pack, pcv ,fuel filter...
02 sensors... have solved it in the past..
perhaps i have another dead 02 sensor..
quite frustrating.
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Old 12-13-2005, 03:55 PM   #14
InsatiableAmos
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While driving around in 4th, i'd stomp on the gas and clutch at the same time to see if the hesitation really was killing the engine...but either i couldn't clutch fast enough to catch the buck just right, or it really isn't dying.

Odd part is, it seems as though the engine doesn't do the hesitation when it's not loaded...not at idle, not while moving and clutch is in, not while revving freely (bouncing revs in the midrange).

Just in thinking about how the whole combustion process works:

Could something be out of adjustment enough that when i floor it and the rpm's are decreasing while it's floored, that the timing gets advanced far enough to slow the piston down rather (while it's on it's upstroke)? Seems like a possibility...and the resulting pulled timing from such an event would prolly put a stop to it quickly (like i've been experiencing).

Is that just an extreme definition of engine knock? Why would i be getting that...subaru says the RS's are designed for 87 octane!!! (currently running 1/2 tank 93, 1/2 tank 87)
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Old 01-06-2006, 01:27 PM   #15
Patrick L
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Well about 1.5 years ago I took my car in to the dealer for a real bad hesitation with no CEL. The tech at this one is a awsome guy and tracked it down to the front 02(A/F meter) as the voltage ready was too low from the 02 and caused the problem. We disconnected the 02 and the car ran fine but rich. Plus when it ws hesitating, if you got the engine over 4k rpm the hesitation would go away. Well guess what happen this week. Out of the blue just before I got too work. It's starts doing the crap again. I disconnected the 02 and it ran fine and enough for me to get too work and go by the dealer to get a new one. I am going to call SOA and ask them what the heck is going on here. This is front 02 #6 for my car(1 of which was my fault). The first one was replace under a Service Bulletin, 2nd when flat bad (CEL for fuel trim Malfunction), and now the last 2 with no CEL and going bad and not giving the right voltage. 00 2.5RS with 160k+.
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Old 01-06-2006, 01:34 PM   #16
Pat L.I.
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after numerous trips to the dealer, i decided to tell them to just throw an 02 sensor at the problem as well as change out my grounding wires which were looking corroded because i have a wrx hood on my car.

im crossing my fingers... but the problem seems to have been fixed. i have been tuning a little with my smt6 and it seems to be smoothing out the issues. its been 5 days and it has not come back yet.
im still experiencing a slight buck at 2,000 rpm sometimes however this may be an issue with my SMT6 configuration.
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Old 01-07-2006, 11:52 AM   #17
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It seems like it is an O2sensor issue, but here is another thought.

What wires and plugs were installed? Please, stay away from Bosch wires and Bosch Platinum plugs. They don't mix well with Suby engines (I have no idea on why, but they cause a lot of problems).
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Old 01-09-2006, 12:15 PM   #18
Pat L.I.
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perhaps i spoke too soon.. still seeing mild hesitation/stuttering..
maybe im running too rich. trying to tune it out now..
frustration station.
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Old 01-09-2006, 12:40 PM   #19
Texas25RS
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has anyone lookd into the evap systeem? my car was having very bad hesitation and stumbling problems immediately after fill ups (the car acted like it would hit fuel cut off at the high end of partial throttle... like when accelerating up an on ramp after the fill up). Some guys on a different board suggested that maybe I was filling p too much and flooding the charcoal canister and associated lines. So I stopped filling up so much and the problem has gone completely away.

Just a thought since most of the ignition system has already been replaced on your cars.
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Old 01-09-2006, 12:50 PM   #20
Pat L.I.
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Quote:
Originally Posted by Texas25RS
has anyone lookd into the evap systeem? my car was having very bad hesitation and stumbling problems immediately after fill ups (the car acted like it would hit fuel cut off at the high end of partial throttle... like when accelerating up an on ramp after the fill up). Some guys on a different board suggested that maybe I was filling p too much and flooding the charcoal canister and associated lines. So I stopped filling up so much and the problem has gone completely away.

Just a thought since most of the ignition system has already been replaced on your cars.

i remember reading that thread... my issue exists no matter what level the fuel tank is at.
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Old 01-09-2006, 01:25 PM   #21
Charlie-III
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Quote:
Originally Posted by Texas25RS
has anyone lookd into the evap systeem? my car was having very bad hesitation and stumbling problems immediately after fill ups (the car acted like it would hit fuel cut off at the high end of partial throttle... like when accelerating up an on ramp after the fill up). Some guys on a different board suggested that maybe I was filling p too much and flooding the charcoal canister and associated lines. So I stopped filling up so much and the problem has gone completely away.

Just a thought since most of the ignition system has already been replaced on your cars.


Thanks.
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Old 01-09-2006, 02:55 PM   #22
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Quote:
Originally Posted by Pat L.I.
i remember reading that thread... my issue exists no matter what level the fuel tank is at.
The point to my post was that maybe you should think a little outside of the box as the solution may not lie in the obvious answers...
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Old 01-10-2006, 09:19 AM   #23
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agreed.. thanks for the suggestion. im open to any help i can get!
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Old 01-10-2006, 01:14 PM   #24
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my MY00 RS did that to me as well. I redid the whole exhaust system and it fixed my problem. haven't had any problems yet and my car is stock. i changed out all the gaskets to the headers, ehxuast, pipes and etcc..and changed the front 02 sensor. see if that helps you.
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Old 01-24-2006, 11:39 PM   #25
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Mmm, I actually changed my cat-back to that of a stock WRX (on my N/A 2.5RS) just a few weeks back, and it did not change the problem. I still have the issue sometimes, but i've isolated it to when the car has just been started cold (and i mean single-digits pretty often: upstate NY here), but happens even though the temp gauge is in the midrange. I make an effort to not push the car above 3k RPM until the temp gauge is at least 1/3 of the way up and the shifter feels appropriately un-balky/loose, so it's not like i'm starting it and beating on it instantly.

Could the ECU still be choking the engine a little? Does anyone have a video/audio clip of a knocking engine? I have an idea of what it sounds like, but i want something to compare it to. Keep in mind this happens with all-octanes, straight 87 piss all the way to the nicest 93 i can find.
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