Bad ground?

[legacy92ej22t]

I've been having a problem with my O2 sensor for about 7 months now and a lot of you are already familiar with the on going struggle but I have new info now.

My blower fan has started not working most of the time. It will however start working sometimes if I screw with it enough (turn off and on repeatedly). I know the blower is on the ground side of the wiring. My car has also started running very similar to the way it runs if I try to use the O2 sensor, even with it unhooked. It acts like I have an extreme vacuum leak. The engine stumbles, idles very rough, almost stalls, vac goes as low as -10 inHg and has major hesitation as I go on boost. It is very intermittent though. The problem with the blower and the engine acting up with the O2 sensor unhooked just started in the last couple days and is inconsistant. When the blower doesn't work, the engine runs bad, when the blower does work, the engine runs good. So, my question is, could this all be related to a bad ground? What do you guys think? Could a bad ground be the reason my O2 sensor doesn't work and why the blower is only working sometimes?

Oh, I'm suspecting the IAC valve too but it would only cause some of my problems.

[BAC5.2]

I was thinking about this when I was on the can. It would seem to me that a bad ground could also be causing my problems. Some electronic intereference could be fouling my O2 sensor wire (which is reading a voltage, even though the sensor is unplugged, and the ECU KNOW'S it's unplugged).

Hmmm.

Matt - If it was the IAC, it'd be hard to know with the FCD, as fuel cut is one of the tell's of an IAC going bad. I have the same problem as you do with not being able to clear the ECU's memory using the connectors-gas-drive method.

My idle is dead on at 1200 RPM, unless the green connectors are connected. Then the idle is closer to 1750.

[vrg3]

The blower and the ECU don't use the same grounds, I don't think. At least not at first... eventually of course they come together somewhere. But, if the blower and ECU are both malfunctioning at the same time, you're definitely right to suspect the power supply setup -- either the ground or the +12v.

Next time you see these symptoms happening, maybe you should try clipping a jumper cable between the ring on the alternator and the negative battery terminal. Or between the negative battery terminal and some of the chassis ground bolts. Or between the alternator and a chassis ground bolt. Or between chassis ground bolts.

Do you still have the factory alternator? I remember in other threads some people found replacing the alternator to help their hesitation problems. If I were nearby I'd suggest each of you try swapping my car's alternator in (it's very easy to swap)... maybe you could find someone nearby with a Legacy who's willing to lend you his/her alternator for a short time.

The FCD you have only prevents overboost fuel cut. It will not prevent a fuel cut due to a malfunctioning IAC valve, a malfunctioning pressure sensor, or anything else that causes fuel cut. If it would make you feel better you can remove it, but if it's properly installed and working correctly it has nothing to do with an idling problem.

[BAC5.2]

Ahh, I didn't know the FCD was only for overboost fuel cut control.

[legacy92ej22t]

Next time you see these symptoms happening, maybe you should try clipping a jumper cable between the ring on the alternator and the negative battery terminal. Or between the negative battery terminal and some of the chassis ground bolts. Or between the alternator and a chassis ground bolt. Or between chassis ground bolts.

I should probably just go ahead and do the grounding mod, huh? It definitely couldn't hurt.

Do you still have the factory alternator? I remember in other threads some people found replacing the alternator to help their hesitation problems. If I were nearby I'd suggest each of you try swapping my car's alternator in (it's very easy to swap)... maybe you could find someone nearby with a Legacy who's willing to lend you his/her alternator for a short time.

No, it's pretty new, maybe 11k miles on it. I do not think it's alternator related.

The FCD you have only prevents overboost fuel cut. It will not prevent a fuel cut due to a malfunctioning IAC valve, a malfunctioning pressure sensor, or anything else that causes fuel cut. If it would make you feel better you can remove it, but if it's properly installed and working correctly it has nothing to do with an idling problem.

Ya, I know about the FCD and I'm sure it's working because I can pull 15 psi without getting FC. I do still get FC fairly often though and it seems to be getting worse (it's worse before my unhooked O2 sensor throws a CEL, then it doesn't happen as often). I wasn't aware that a bad IAC could cause FC! I wonder if that's my problem. Could a bad IAC be causing the problems with my fuel trims? That'd be great if it's that and it just needs a good cleaning.

[BAC5.2]

The IAC's fail-safe is fuel cut when any of the paramaters are exceeded (I.E. if you decide to cruise in 4th at 40mph, then downshift to 2nd and try to haul ass, it'll cut fuel. If you are consistantly redlining every gear, you won't hit cut.) An eratic idle is also a result of a bad IAC.

Unfortunately, a good cleaning isn't a fix. I attempted to clean mine, and had nothing but ineffective results.

I hate having computer problems! My idle is REALLY stable @ 1200 RPM right now, but that's still 500 above normal, and there are new problems manifesting themselves every day.

Earlier today, i put the car in neutral to slow down for a stop light, and the car was still "idling" at the RPM I let off at (3k). Whatever the problem is, I need to fix it.

[ultrasonic]

Earlier today, i put the car in neutral to slow down for a stop light, and the car was still "idling" at the RPM I let off at (3k). Whatever the problem is, I need to fix it.

Maybe your throttle cable is sticking.

[BAC5.2]

Could be, a throttle blip fixed the problem.