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Old 07-14-2012, 09:58 PM   #1
ericrally
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Default Can a bad 02 sensor render a car undrivable?

I bought a 2.5l 2002 outback sport today. When i test drove it, the car ran great with nice power. I started driving it home, made it about 50 miles and suddenly the car starts stumbling horribly. I pull over, check the connection on the idle and tps sensors and get back on the high way. Its still jerking if I use over half throttle but its enough to keep up at highway speeds.
I make it about ten more miles when the car looses all power and throws a code for the front o2 sensor. I go through, clear the codes and get back o nthe road to see that the problem is gone. After about ten more miles it come back just as bad and I coast to a stop. I barely make it home.
Obviously a o2 sensor can make the car run badly, but can it make the car completely lose power to where it wont accelerate with the pedal floored?
Thanks!
Eric
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Old 07-14-2012, 10:48 PM   #2
jefferyhanselman321
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Sounds more along the line of a fuel pump or filter, I had a pickup that did that before and it was a bad pump. Might try and test drive it with a gauge and see if it holds pressure, I don't know the exact psi that it should be though. Good luck, hopefully you get it fixed.
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Old 07-15-2012, 07:44 AM   #3
ericrally
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The car has a new filter and fuel pressure regulator, so it may be the pump...
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Old 07-15-2012, 08:41 AM   #4
GrundleJuice
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You could unplug the o2 and the computer will rely on pre set fueling tables and ignore the o2. If that fixes it, or makes it much better then I would replaced the o2
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Old 07-15-2012, 11:33 AM   #5
ericrally
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Great advice! I have to replace it anyways, but that would tell me right away. Thanks!
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Old 07-15-2012, 11:35 AM   #6
Elbert Bass
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Without the actual code number it's hard to point you in a specific direction since there are at least 7 different codes for front O2 sensor. More likely the code is the result of the O2 sensor reading a too rich or too lean condition. I would look for the cause of that condition.

Sad too say but just as a ballpark guess catalytic converters can cause symptoms like that. Usually it causes loss of power @RPM all the time though. What may be happening is the vehicle goes rich at steady highway speeds and eventually causes the cat to overheat - swelling up and partially blocking the exhaust. That's a shot in the dark but I have seen it happen before.
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Old 07-15-2012, 01:40 PM   #7
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O2 sensor - will run like ass at partial throttle, will run great dead cold startup and under heavy throttle.

When bad the car will have problems idling and will cut out horribly at partial throttle. You can drive the car but you will be driving swapping between heavy throttle and coasting. At lights while stopped, you must rev the engine some to prevent the car from dying. It will cut out a lot idling, but you can maintain enough rpm to not stall the car. I'm talking about a completely shot O2 sensor here. As it fails, it slowly gets worse. The miss will be light and intermittent first. Then it slowly gets worse and worse until the car is almost undriveable under closed loop. During open loop the car will run great because it's ignoring the sensor. It will be in open loop right when you start the car and during heavy throttle (say +75%). This is when the car is driveable.

O2 failure is primarily a contamination issue. It will foul out over time, a very long time, if the engine is running well. If the engine is running poorly, mainly burning oil, it will foul out much faster. For example if the engine sends a few quarts of burn oil through of the next couple months, it will likely be enough to prevent the O2 from functioning. My record is 3 months to run a completely new O2 sensor from oil contamination, but that's me going to an auto-x on the weekend and gulping down a quart of oil (old engine running low viscosity oil). I don't want to scare you into thinking your car has a worn engine, but O2s typically last for a very long time with a well running engine. O2 failure is often a sign of burning oil. Pull the O2 sensor. If it's just covered in black carbon, you're burning oil. If you're running a 5w30, step to a 5w40 and watch consumption. There are 0w50 and 5w60 weights too...if needed as these will allow very minimal oil consumption on very worn motors. Each step up pretty much halves consumption. Also understand the difference between light driving and hard driving on consumption. You can spend a month using up 1 quart with light driving. You can use up the same quart on the same engine in a day with hard diving. An air/oil separator can also help with this by catching all the blowby coming back through the vent lines from the crank case and valve covers. Before all of this, just spend some time and verify the amount of consumption you have...if that is even the source of the O2 failure.
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Old 07-15-2012, 09:59 PM   #8
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Okay thanks for the advice!
I pulled the o2 sensor and drove the car down the road, and the symptoms are still there. I went ahead and ordered a fuel pump to try that.
The car idles perfectly, and feels perfect up until about 4000 RPM. Then it bogs really bad. If I floor it, the car will either completely lose power or bog then rev, bog then rev until I release the throttle. It seems to be based on the load on the engine.
It looks like the sensor was recently replaced with an aftermarket one that appears to have gone bad...
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Old 07-15-2012, 10:54 PM   #9
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Try re setting the ecu, see if it is instantly better and slowly gets worse.
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Old 07-16-2012, 06:27 PM   #10
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Reset the ECu and it seems to be about the same. Its not nearly as bad as when I drove it home on the highway, its actually drivable now.
Interestingly, in neutral if I use half throttle and I can slowly rev the car up to red line. If I push the throttle wide open it bogs down and wont rev over 4000. What does that sound like?
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Old 07-16-2012, 07:26 PM   #11
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A clogged air filter

Seriously though, what is the code that it has been throwing?
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Old 07-16-2012, 07:37 PM   #12
ericrally
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P0130 Front o2 sensor...
Which it was replaced a few months ago by the previous owner, but its probably a cheap aftermarket sensor that failed.
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Old 07-16-2012, 08:25 PM   #13
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I also noticed the car always jerks when releasing throttle to coast. its not smooth ever... Im thinking it may actually be the neutral position sensor on the transmission as someone else had almost identical symptoms and replacing it solved it, but the cruise control works fine and cuts off when I push in the clutch....
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Old 07-16-2012, 10:55 PM   #14
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Quote:
Originally Posted by ericrally
Reset the ECu and it seems to be about the same. Its not nearly as bad as when I drove it home on the highway, its actually drivable now.
Interestingly, in neutral if I use half throttle and I can slowly rev the car up to red line. If I push the throttle wide open it bogs down and wont rev over 4000. What does that sound like?
If you hold it wide open will it die? Can you smell gas out of the exhaust if you make it bog down?
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Old 07-16-2012, 11:00 PM   #15
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Quote:
Originally Posted by ericrally
I also noticed the car always jerks when releasing throttle to coast. its not smooth ever... Im thinking it may actually be the neutral position sensor on the transmission as someone else had almost identical symptoms and replacing it solved it, but the cruise control works fine and cuts off when I push in the clutch....
I've had the same issue in my foz for a while and it makes it idle just a little high but never a set idle. Have legit replaced every engine sensor and did a full rebuild. Im going to pull my O2s tomorrow and see how they look.
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Old 07-17-2012, 10:54 AM   #16
scarney1988
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Can you report any of your freeze frame data?

Normally a bad fuel pump will be associated with a lean condition code, possible P0300 (intermittent P030#) code. Although a coated sensor will normally report a low oxygen content (rich mixture) and send the fuel trims negative causing the issues, if its the sensor.

If operating your clutch pedal (from what I understand you have a manual, although I couldnt find it expressly written out) disengaes the CC, and starting car is impossible without the pedal being depressed first, than you are probably okay there.

could you please report your freeze frame data? Particularly ECT, TPS, IAT, O2v front, FT's (short and long)....

What is your coolant level like?

If you can post that stuff I may be able to help you get started.

g-luck
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Old 07-17-2012, 06:22 PM   #17
ericrally
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Thanks for the help!
If hold it wide open it just sits at 4000, and will bump up to 5000 sometimes then back down to 4000. I cant really smell any gas when it bogs....
I pulled the o2 sensor loose and it seems to act the same with the 4000 rpm bogging...
I dont have freeze frame data for the code with my scanner, but the coolant level is perfect...
Thanks!
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Old 07-17-2012, 09:48 PM   #18
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Well I just tried swapping out the crankshaft position sensor from my 2.5RS, and took it down the road. It revved and ran perfectly and I thought I had finally found the issue, but as the car warmed up it slowly came back and driving in second with the throttle wide open it consistently bogs at around 4000 rpm and jerks and surges. Almost like its hitting fuel cut off...
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Old 07-17-2012, 09:55 PM   #19
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First of all why did you order a fuel pump. Did you do any fuel pressure tests to back that up? Scarney hit it excatly, check your freeze frame data and see where your fuel trims and af readings are. Track your graph to see if you indeed do have a dead a/f, or a lagging a/f. Go from there. Don't like to throw parts at it but just replace the thing and see if it changes instead of unplugging it and so forth.
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Old 07-17-2012, 11:10 PM   #20
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Does it always run normal when cold and then go back to the problematic ways when it's warm or was that just once after the crank position sensor swap?
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Old 07-17-2012, 11:35 PM   #21
ericrally
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It was just after the sensor swap...
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Old 07-17-2012, 11:37 PM   #22
ericrally
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I dont have a scanner that can show freeze frames. Ive been swapping out parts that I know work, there can only be so many sensors that can cause this right? If I cant track it down Ill just have to take the car to a shop to diagnose it, but I wanted to at least try since I have anther car with a near identical motor that I can swap parts off...
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Old 07-18-2012, 11:41 AM   #23
scarney1988
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My suggestion to you would be to get a small autel or actron scanner than can display freeze frame and live data. They can be had for much less than the cost of many new sensors. That will save you so much money and head ache that you will wonder why you didn't do it sooner. Honeslty, dianosing a driveability concern with the proper tools isnt always easy, and with out them it can be near impossible.

Disconnecting the forward 02 will drive the mixture rich and cause most of the symptoms you are having (bogging, bad idle, no power, etc...). A forward 02 sensor can cause many many whack problems depending on its signal output. P0130 is set after 20 seconds of out of range signal output (specifically signal beneath 0.4v for more than 20 seconds). That could point to a few different areas. I found a nice concise list of possible trouble areas you to check.

Water or corrosion in the connector
Loose terminals in the connector
Wiring burnt on exhaust components
Open or short in the wiring due to rubbing on engine components
Holes in exhaust allowing unmetered oxygen into exhaust system
Unmetered vacuum leak at the engine


Bad o2 sensor
Bad PCM


I am not familiar with your particular engine configuration and maintenance history so I'm going to ask some questions to help everyone help you a little better:
  1. Does the car have one ignition coil, or coil on plug?
  2. If it has one main coil, have you tried swapping that?
  3. Have you ever performed a tune up (replaced spark plugs)? If so with what brand and type and when?
  4. Is the new fuel pressure regulator vacuum operated? If so, is the vacuum line connected properly?
  5. Are there any exhaust leaks that you an hear?
  6. Do you have any diagnostic tools (DMM, fuel pressure gauge, etc...)?


g-luck, we'll get ya through this eventually lol. If you are gonna go to a shop, throw a sensor at it first. The shop will most likely charge you an hour diag, and then tell you they have to put a sensor in it before the can continue diagnosing.
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Old 07-18-2012, 05:22 PM   #24
ericrally
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It was the fuel pump!!!
Thanks for all the help everyone, it runs perfectly now, cant wait to see how it does when I put the new 02 sensor in...
Ill definitely be getting a good scan tool in the future.
Do you recommend the actron over the Equus? Im looking at getting anEquus Innova 3130.
Thanks again for all the advice to get this sorted out!
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Old 07-18-2012, 09:03 PM   #25
scarney1988
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Congrats!

I have an Autel Maxiscan MS309 and I love it. Does IM readiness, code pulling (with code desc), live data, and is works on CAN cars.

You wont go wrong with actron or equus either. Both are reputable brands. Just make sure you get one that does what you need
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