Tofubento

Ive searched and cant seem to find an answer to this one...

I had a P0175 code, turns out every vacuum line decided to break at once on the same day.

Fix that, car drove great for a week, then P0174 code...lean bank 2. I have new plugs, new hoses, new filter, and no cracks in air box or anywhere. I pull everything apart, and check out anything and everything. Nothing wrong, connect everything back up, CEL goes off. Drive around for a day, and its back and kicking back the same code. So, do some more research, some have said MAF has gone bad...so replace the MAF. Code is still there. Do the same disconnect and reconnect, and code is off. Get rear ended and code come back on ( dude drove off ASAP...thank you Vegas ) So check it and its the P0174 code again. Do the same thing, code goes off and car is fine...short while later code comes back on. ( Throttle body and MAF where cleaned prior to trying out a new MAF to fix the problem )

Now the thing is, once the code goes off the car feel super smooth, no vibrations, acceleration is great...but then it will start to have a slightly rough idle ( most cant feel it i am weird ) and then the light comes on.

Has anyone had this happen or have an idea how to fix it?

MikeFig82

iTrader: (13)

To me it seems the upstream 02 sensor might not be working. Which car do you have GS3, or 4XX?

Since you changed the vac lines, and cleaned the throttle body. The fault is behind the MAF. I don't have my car anymore so I can't remember really. I think the vac lines also run down the car to the emsions canistor. Then back to the front of the car again. I had a GS400 though. You could try to traces those lines.

Mr Jokster

iTrader: (8)

Because you're initial problem was with vacuum lines, I think there's still a problem.

Did you ever run a fog/smoke test? Thats the best way to find where there may be yet another leak.

Tofubento

Havnt done a fog test...didnt actually think about that.

I have a 430.

Its really bloody irritating.

Tofubento

and today its off and everything is running fine. Spoke to an old friend ( BMW tech ) and he said maybe a bad batch of gas? Just bloody weird. Replaced all the vacuum lines, and the MAF and had the code for a day, ran kind of rough, now its off, and running smooth as hell.

Tofubento

Okay so went through and replaced every single hose and clamp...found 1 hose and 4 clamps I missed. So far its running okay, still running a pending code of P0174. I am getting bloody tired of this. Has anyone else run into this? Still havnt had a chance to do a smoke/fog test at the lines, had some other expenses come up. So if I cant figure it out, going to try that, and if nothing shows up..I am just going to bang my head against the wall until I pass out. Because...holy f this is annoying.

vijayn

Are you able to check if the oxygen sensor works? If you get a scantool on live data mode, choose all data related to the oxygen sensors and accelerate your engine while in park and see if the voltage goes up or you get a rich condition on the live data. Other check is you can directly measure the voltage with a multimeter or scope and try the same test.
Lean = 0V - 0.2V
Stoich = 0.4 - 0.6V
Rich = 0.8V - 1V

If its working properly, then you should get a voltage of around 0.8V (rich) when you rev it. If you don't, then try spray some liquid fuel down the intake and see if that makes it go to around 0.8V (rich). If the voltage remains at 0V for all of the tests, then you either have a faulty oxygen sensor or a bad leak on the exhaust manifold.

Tofubento

Guess ill have to pick up a multimeter. Never used one before, so this will be a fun learning experience. No scan tool, just a basic obd2 reader. This is what its showing :

02B1S2 (V) .820 ( bounced around a bit, but close to that )
02B2S1 (V) .80 ( ^^ )
Short fuel B2S1 5.5%
Short fuel B1S1 0.0%
02B1S1 (V) .05 - .60 ( bounced around but low range, maybe this is my problem area)
MAF (g/s) 3.75
Long Fuel 1 24.2%
Long Fuel 2 25.8 %
Short Fuel 2 7%
Short Fuel 1 0.8%

Edit :

This morning, drove to the gym and then back home. Cat all warmed engine warmed, plugged in and did some live data, and this was the big change.

02B2S2 (V) : 0.115 - didnt move even when on throttle or off throttle, even held at 1.5k and 2 - 2.5k.


Makes sense that this would be the culprit since I keep getting bank 2 low.

02B1S1 functioned normal, didnt run low this time.

This is still frustrating.

vijayn

Good work there.
There's actually 4 oxygen sensors to measure -
bank 1 sensor 1
bank 1 sensor 2
bank 2 sensor 1
bank 2 sensor 2

The sensor 1 oxygen sensors are pre cat and the sensor 2 oxygen sensors are post cat.
By the way I have seen mistakes on some scantools where they give the wrong readings so I would test them with multimeter just to be sure.
But judging by your post, bank 2 sensor 2 isn't looking good.\

Also the fuel trims for long term are way too high. They should never be <10% positive or negative. Your one is positive around 25% on both banks meaning, the system had to add an extra 25% injection pulse to the injectors to keep the emissions good.
Are both sensor 1 oxygen sensors cycling between 0.1V - 0.9V when your engine is warmed up and at idle condition?

Tofubento

Yeah I noticed that about the longterm, seemed astronomically high.

Question on the sensors is they are within the normal/rich range as you pointed out in your previous post.

I wonder if I should knock out the other sensors as well, and see if that will help. Buddy still says its just a vacuum leak, because it will be on, then off. But I have replaced every vacuum line and hardware. Checked the airbox, everything that could possibly leak and I cant find anything. They only thing I can think of is its the 02 sensor.

vijayn

There are two main modes for the oxygen sensors to work in. One of them is the closed loop mode where the fuel trims learn off of what the oxygen sensor voltages are at. For a good sensor the voltage should cycle between lean and rich for about 10 times per 10 seconds. The condition for learning needs to be warmed up and idling.
The other mode is open loop mode, where fuel trim doesn't learn but applies its learnt values to the injection pulse width. The oxygen sensor voltage will either be lean or rich but wont be cycling. This is usually when it still cold or your de-accelerating or accelerating.
When you reset your system by taking the battery terminal off for a period of time, it actually resets the long term fuel trim learnt values and the ECU has to relearn the values again. This explains why the code goes away but returns after a period of time of learning.
Just to be sure are you able to spray liquid fuel inside the intake while checking what happens to the voltages of the oxygen sensors? This would help to determine if it really is the oxygen sensors or something else (exhaust leak, injectors, fuel supply etc...).

Tofubento

Thank you for the additional info, been reading everything I can online on this.

Going to see what happens with some starter fluid, and go from there.

Tofubento

So, odd turn of events.

Got some starter fluid, and did like a friend taught me to check vacuum leaks, and did what Vijayn suggested. No change in the voltage in anything. Until I got to the throttle body vacuum lines. The sensor became active, along with everything else. So, I went and isolated each vacuum line and sprayed it with the starter fluid. None of them changed any of the live data, that is until I sprayed right at the throttle body gasket. Then the numbers came to life, including the second bank sensor, which I didnt think was getting any voltage, or next to none. It started jumping around as you said , Vijayn.

So, going to see if the gasket could be the problem. But if its not, at least I replaced a 15 dollar gasket that I am sure could be replaced. A few miles away from 200 thousand.

vijayn

Great, that proves that the oxygen sensors are able to give out a rich voltage which means something else is causing the lean mixture. That TB gasket seems like the problem aye

Tofubento

Gasket on order and on the way. Lets hope this fixes it lolol