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91 Legacy Turbo erratic excelleration


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  • 2 weeks later...
When I installed the temporary OEM downpipe on my wagon a few years ago, the intake was really loud. The cat was fully plugged, but I don't recall clearly if there was any turbo noise. Might find a take-off OEM WRX downpipe off NASIOC or Craig's List and toss it on. Heck, find a WRX owner who will let you borrow theirs and do it all for free!

 

 

I installed a 3" downpipe and the problem is still there. I couldn't see clearly enough if the remaining cat was clogged or not though.

 

I think I'm having issues with the knock sensor wiring. What's a good scan tool for this obd1?

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  • 3 months later...
  • 4 weeks later...

I'm still dinkin around with this thing!

 

Quick recap of the issue: When the engine is cold (running for less than an hour or so) I cannot get the car to accelerate smoothly. It whistles and makes a "shk shk shk" sound like a wastegate or bov is opening when it isn't supposed to. If I hold the throttle at 1/3 or so, it will sometimes bog and then out of nowhere it will make great power, and then bog, etc.

 

When the engine has been driven for a long time, it runs very strong. But when I'm WOT at ove 80mph, it will surge. It really feels like my timing is all over the place. It did seem to get a little better when I replaced the knock sensor but it didn't fix the issue. I wonder if I just moved the wire harness around enough to make the ecm happy for a while.

 

It only thros a "purge canister solenoid" CEL and I don't think that would have anything to do with this. I'll delete it soon with a 100ohm resistor anyway.

 

So far I have replaced:

 

PCV, plugs and wires, fuel filter, air filter, knock sensor, ecm coolant sensor, timing belt tensioner, belts, O2 sensor, wastegate solenoid, fuel pump,

 

Troubleshooting steps:

-Installed water/meth injection to see if I had actual detonation.

-Installed 3" downpipe and deleted front cat.

-Checked crankshaft for timing gear key damage.

-Going to try grounding mod next...

 

I know I'm missing some things here.

I tried using vrg3's scantool, but I couldn't get it working on my old school laptop. Something wrong with the parrallel port I think.

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I'm not much help, but reading the previous post one thing jumped out at me. . .

You state that your car runs 'cold' for the first HOUR of operation, then warms up and runs fine?!? If your engine is cold for that long, that is a problem. The problem then goes away once the engine is at running temp?

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I'm not much help, but reading the previous post one thing jumped out at me. . .

You state that your car runs 'cold' for the first HOUR of operation, then warms up and runs fine?!? If your engine is cold for that long, that is a problem. The problem then goes away once the engine is at running temp?

 

I should have clarified. The car gets up to temp just fine in a matter of minutes. BUT- the surging continues until the engine, and maybe everything else under the hood, gets good and hot. This makes me think some kind of sensor or solenoid is not working well until it's really hot. On cold days, the engine would run like crap most of the time. On hot days, it runs like crap for an hour or so, then it runs much better.

 

I'm going to try grounding the O2 sensor and the knock sensor directly to the block.

 

Dang, I wish I could get vrg3's program to work for me!

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I'm going to try grounding the O2 sensor and the knock sensor directly to the block.

 

I don't know about doing that, but you might need to replace your knock sensor wiring. You can run a new shielded wire from the ECU to the sensor. It is in a perfect spot to get rubbed in the engine. I think that's what I need to do with mine. The changing timing would definitely point to a knock sensor issue if your belt isn't jumping teeth left and right! :)

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It seems to be working great after messing around with the wiring. There must be a bad wire in there and I left it in a good spot or something. I have bunch of aicraft shielded wire so I might as well just replace it all the way back to the ecm.

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