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Old 03-12-2012, 06:56 PM   #1
affekonig
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Join Date: Sep 2010
Default 98 Legacy 2.5 crank sprocket damage? Rough idle, popping, low power

Long time, multiple WRX owner, very low poster...

Anyway, I picked up a non-running 98 Legacy Outback with the NA 2.5 recently. I figured the timing belt had broken (never even heard it turn over before I got it home), but it turns out that the belt was off a few teeth. I replaced the belt and idlers, lined everything up, put it back together and it started right up...other than the loud clanging. It was my fault as I forgot to space the tensioner pulley out with a washer and the tabs on the crank sprocket were hitting the pulley. I took it back apart, put the washer behind the idler and it starts and runs fine when it's cold. The tabs on the crank sprocket were scratched/grooved, but not broken from their run-in with the idler.

So, it starts and runs fine cold, but starts idling really, really rough when it gets to operating temp. It will also accelrate like it's running on three cylinders from a dead stop and will pop in the exahust. All of the problems occur when it's in closed loop mode, so I'm pretty sure I'm looking at a sensor issue. I was told the car ran fine before it just died and I assume it died because of the timing belt being off. If it did run fine before the timing belt slipped, the only thing that's changed is the damage I did to the tabs that I'm assuming the crank position sensor uses to rear the crank position. Sound right?

Also, the idle clears right up if I unplug the TPS, but the popping/low power from a dead stop remains and the car acts like...it doesn't have a TPS hooked up. Does unplugging it put it into open loop? Also, unhooking the front O2 sensor didn't seem to change anything. Sorry for the long firstish post. Any thoughts?
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Old 03-12-2012, 11:37 PM   #2
ManualOverAuto
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2001 Impreza L coupe
Sedona red Pearl

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Quote:
Originally Posted by affekonig
Long time, multiple WRX owner, very low poster...

Anyway, I picked up a non-running 98 Legacy Outback with the NA 2.5 recently. I figured the timing belt had broken (never even heard it turn over before I got it home), but it turns out that the belt was off a few teeth
I know if timing belt breaks valves can get bent but maybe it could happen if timing is off too many "teeth" also? How many is a "few teeth" in your case?

Bent valves can give you low compression right? That would account for the loss of power.

My .02
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Old 03-13-2012, 10:50 AM   #3
affekonig
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Yup, it can cause low compression and there is one valve that's ticking, but it was only off two teeth and I never heard/felt anything hitting. The valve tick is probably louder than it should be, but I'm hoping that it's more related the the 155k miles and less the timing belt issue. Maybe wishful thinking. It does run well cold though, and that's why I'm sticking with the possibility that it's a sensor issue. I'm going to do a compression test one of these days, but the main question is: Is it possible that the lightly damaged fins on the crank gear are causing problems? I haven't found much on the crank position sensor and how tolerant it is.
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