need help troubleshooting

[Monkhouse]

My car is hesitating when I step on the gas and at idle. It feels like it's misfiring. Before I start replacing ten and twenty dollar items trying to guess, I want to narrow down the possible causes. I borrowed an OBD2 scanner from a coworker, and got no codes. My check engine light is not on. The scanner did indicate that the self diagnostic check did not finish for the catalyst, evaporation, oxygen, and oxygen heater systems. I'm not a mechanic, so I'm not sure what all this means.

Money's tight, so I really need to get this right the first time.

Any suggestions would be greatly appreciated.

Thanks.

[Huffer]

When was the fuel filter last replaced? Have you started buying gas from a different station?

[Monkhouse]

To my knowledge, the fuel filter has never been replaced. I was leaning towards that, as well, but I'm wondering if that's really it after the OBD2 scan. Could a clogged fuel filter cause problems with those other systems?

[Sarra]

Fuel filter
Spark plugs
Wires

I know my BK did the hesitate thing, after I put in VPower plugs and spent a massive amount of money on wires, it went away. I also installed a grounding kit.

[Chicago96GT]

I got this right agter i installed the v-powers also. Did you ever end up changing these or did it just go away. I still have this problem and was going to try the fuel filter but also money is really tight right now. Would love to know why its doing this.

[Monkhouse]

Fuel filter
Spark plugs
Wires

This was exactly my train of thought, too. I was also thinking of changing the air filter, as well. Plus, after the OBD2 scan, I'm wondering if it could be an oxygen sensor. I'm worried, though, because each one of these that gets replaced without actually fixing the problem is food I'm not putting on the table for my wife and kid. That's a bit dramatic, but basically it comes down to money. I can't afford to replace all of these things at one time, so I'm trying to come up with the best guess before I rush out and start buying parts.

[Monkhouse]

Well, it's been a car repair weekend. New brakes, pads and rotors all the way around. Not related to this problem, but it was a chunk of work anyway.

New fuel and air filters, but no fix to the problem. Now I get just a little hesitation at idle, and a lot when I step on the gas. when I try to accelerate herder, I get a little backfire. That's new.

The filters set me back about $30, so I'm done guessing until I get paid on Friday.

[Sarra]

If you don't replace bad spark plugs, your wires will go bad. If you don't replace bad plugs and wires, then your coil pack will go bad. Bad coil pack = WAAAAAAY more expensive than just plugs or plugs and wires.

[AJM]

Vacum leak maybe?

[Monkhouse]

The spark plugs get replaced once a year, in the spring. The wires and coil pack were replaced about two years ago. The next thing I'll be doing is the spark plugs, but it has to wait till Friday, there's just no way around that. Zero money = zero parts.

I still can't get past the reading from the OBD2 scan. The car's self diagnostic wont run on the catalyst system, the evaporation system, the oxygen system, and the oxygen heater system. I'd love to know the common denominator between those.

[Huffer]

Common denominator is likely to be the front O2 sensor.

[Rockgod]

you really should look at those spark plugs. once a year IMO is not a good thing. as for the backfire that also could be the plugs if they aren't installed correctly. uneven plugs can cause backfire. just take a look at them. do you have the latest repair manual from haynes? that would be good way to diagnose a problem. the book code is 89101 - MY 2000 to 2006 Legacy and Forester. model years before that I believe is 89100. check your local auto shop if they have it. if not tell them to order it.

good to have when you can't get to a computer. :cool:

by the way I change my plugs every 3K. you should consider the same.

Good luck with finding the problem

[Monkhouse]

I've been trying to not drive my car while I have this problem, but it's tough sometimes. Today, my wife needs her car, and it's sposed to rain, so no motorcycle. When I got to work today, I nearly got out and did a little dance. My check engine light is on. Sweet F&#$ing Christ, my check engine light is on!! I haven't been this excited in a while.

Now I just have to wait for the 2nd shift guy I work with to bring his OBD2 scanner in. He'll be here in 4 hours, and it seems like it's years away.

[Monkhouse]

Well, it's the knock sensor. Error P0325. After a little research I found a couple threads on here about this exact error, so after this post I'll let this thread die. A little more research in the literature and manual section and I found a document that has a procedure to use a voltmeter and an O-scope to verify that it definitely is the knock sensor.

Here's a link to it if anyone wants it:
http://www.veloce.pwp.blueyonder.co.uk/DiagnosisEGI.pdf

Once I verify it, I just need to park the car until I have $75 to get a knock sensor. Shouldn't be more than a couple weeks.

Thanks for all the suggestions everyone.

[deadlydave]

Well, a u-pull-it junk yard will let you have it cheaper, but you gotta remove it.

Also, FYI for any people with the same problem, the 2.2 knock sensor and 2.5 DOHC knock sensor are not the same part.