Infamous P0171, I need help on this one

[im2bad4ya]

So I've had this code come up in the past and I know it means I'm running lean. But all my vacuum ports are fine, I've checked them all and they're all connected with no leaks, I'm reading 21 vac at start up and 20 after the car is warmed up and I'm in idle. I was leaking air through the o-rings in the fuel injectors when I got the code a few weeks ago but I've since sealed them properly.

So I basically have three questions.

1. Which sensor or sensors make the P0171 code go off?
2. What other trouble spots should I look to for air leaks?
3. There's slight air coming out of my o-rings but not at all like before. Do my o-rings have to be absolutely air tight?

 

[Dr0]

air coming out of O-rings? im assuming your talking about injectors??? they should be sealed completely and they wouldn't leak air they would leak fuel if they don't seal correctly. as for the lean code... the 02 sensors are responsible for setting this code and it just means the 02 is reading more lean and is switching from lean/rich as it should, most likely you have an exhaust leak somewhere since your vacuum is good. just start the car up and slowly float your hand around the suspect areas to feel for warm puffs of air (aka the leak) if you aren't sure if you found one or not have a buddy put his hand over the muffler to build excess pressure in the exhaust making the leak puff harder (since its trying to escape) and thus verifying said leak

 

[Dr0]

it could be other things but ive seen a lot of people get lean codes from exhaust leaks on the forums and at my shop. having a vacuum leak can sometimes cause a lean code too but "IF" your 02 sensors are in good working order the car can usually add or subtract the fuel trims to correct the issue. if you showed me your short term and long term fuel trims I can pretty much tell you whats wrong

 

[hornsfan10609]

P0171 is typically a vacuum leak when my car throws it, I would keep looking at all the vacuum lines and check if the wastegate holds pressure when you blow in the line.

 

[im2bad4ya]

it could be other things but ive seen a lot of people get lean codes from exhaust leaks on the forums and at my shop. having a vacuum leak can sometimes cause a lean code too but "IF" your 02 sensors are in good working order the car can usually add or subtract the fuel trims to correct the issue. if you showed me your short term and long term fuel trims I can pretty much tell you whats wrong

Damn, I hope it's not the sensor, it'd be the second sensor I go through in a year. My vac and A/F gauges are all reading correctly as they should. I'll try to check for an exhaust leak. I have a corksport catback with J-pipe and stock S pipe. I'll cover the exhaust with a rag and check for leaks in the exhaust.

Also as far as the fuel trims, I have an SSAFC but I'm not sure if that can log the data you're talking about. For now it's bypassed because I have my state inspection coming up and last time I had it connected i threw the same code.

 

[PSUENGR]

As hornsfan indicated it could be your wastegate actuator. That is what was causing my code. Disconnect the vacuum line leading to your WGA and try to blow into it. If you can push air into the line then the diaphragm is probably shot and you are over boosting. I'm guessing you have a boost gauge so you could probably also watch that closely and see if you're running extra boost or getting any large spikes.

 

[Schwamm]

I got this code 3 times in the past year presumably because of an exhaust leak at the manifold (it wasn't bolted on tightly). If your vacuum pressure and WGA are good you might want to check that. I fixed it a month ago and haven't had any issues yet (fingers crossed)

 

[im2bad4ya]

As hornsfan indicated it could be your wastegate actuator. That is what was causing my code. Disconnect the vacuum line leading to your WGA and try to blow into it. If you can push air into the line then the diaphragm is probably shot and you are over boosting. I'm guessing you have a boost gauge so you could probably also watch that closely and see if you're running extra boost or getting any large spikes.

One of the times I had a the P0171 CEL was from a busted WGA. Mine is not even 6 months old and like I said, vac reads solid 21. When the WGA was busted it was around 18-16. I'll test it thought but I doubt it.

I got this code 3 times in the past year presumably because of an exhaust leak at the manifold (it wasn't bolted on tightly). If your vacuum pressure and WGA are good you might want to check that. I fixed it a month ago and haven't had any issues yet (fingers crossed)

My manifold has a slight hairline crack on it but nothing leaks out of it. I'm gonna JB weld it anyway and check out the whole exhaust systems for leaks though. I'm almost 100% positive it's not a vacuum issue.

 

[turbomsp2003]

ive tried jb welding my turbo mani and it started to smoke lol i thought my engine had caught on fire

 

[turbomsp2003]

ive also learned to live with my check engine staring at me every time i drive my msp....had taken to a mechanic that smoke tested and i have no vac leaks and he also couldnt find leaks in my exhaust he tested fuel pressure and injectors with no problems and also replaced my o2 sensor but he says car is running perfectly and that it wasnt harming anything?????

 

[jumaaneface]

ive also learned to live with my check engine staring at me every time i drive my msp....had taken to a mechanic that smoke tested and i have no vac leaks and he also couldnt find leaks in my exhaust he tested fuel pressure and injectors with no problems and also replaced my o2 sensor but he says car is running perfectly and that it wasnt harming anything?????

It's mostly likely your wga if you can't find any other vacuum leaks. Exhaust leaks aren't that easy to find in my experience with this car. I found all mine with seafoam and revving from under the hood.

 

[protege3690]

probably your exhuast mani. even though its a hairline crack. it can still leak. or its not secured tightly against the head. if his vacuum is good then his WGA should be good. at least in my experience thats what its been. when my WGA was shot. my vacuum dropped down to about 14 from 21/22.

 

[PSUENGR]

ive also learned to live with my check engine staring at me every time i drive my msp....had taken to a mechanic that smoke tested and i have no vac leaks and he also couldnt find leaks in my exhaust he tested fuel pressure and injectors with no problems and also replaced my o2 sensor but he says car is running perfectly and that it wasnt harming anything?????

I wouldn't necessarily say that is the case. The car runs rich as is, if it is sensing a lean condition it is likely throwing even more fuel into the mix. My guess is this will have a negative affect on your cat at the very least and likely will lead to a lot of carbon buildup elsewhere. There are some check engine codes that I wouldn't be too worried about, but a running lean code isn't one that I would let go on a permanent basis. That is if I intend to keep the car for a long time. My msp has recently been relegated to beater/winter car as I picked up a clean e46 330i and even though mine is running great right now, the next thing that goes wrong that costs more than a couple hundred bucks isn't going to get fixed.

 

[im2bad4ya]

probably your exhuast mani. even though its a hairline crack. it can still leak. or its not secured tightly against the head. if his vacuum is good then his WGA should be good. at least in my experience thats what its been. when my WGA was shot. my vacuum dropped down to about 14 from 21/22.

My vac was reading 16 when i had a busted WGA. I just finished JB welding the the hairline crack, and retightening all the intake clamps and vacuum clamps, we'll see if it makes a difference.

I wouldn't necessarily say that is the case. The car runs rich as is, if it is sensing a lean condition it is likely throwing even more fuel into the mix. My guess is this will have a negative affect on your cat at the very least and likely will lead to a lot of carbon buildup elsewhere. There are some check engine codes that I wouldn't be too worried about, but a running lean code isn't one that I would let go on a permanent basis. That is if I intend to keep the car for a long time. My msp has recently been relegated to beater/winter car as I picked up a clean e46 330i and even though mine is running great right now, the next thing that goes wrong that costs more than a couple hundred bucks isn't going to get fixed.

Lucikly I don't have to worry about a cat, I'm catless

 

[im2bad4ya]

JB welded the exhaust mani and the code just came back anyway. I might have a leak though because when I covered my exhaust n gave it gas smoke was coming from the engine bay, so I'm gonna continue getting at this problem until I've exhaust all options (no pun intended).

Also, would the backup O2 sensor throw the code? I have a O2 defouler just like this one:

I used the middle plug but maybe I need to use the one that restricts the most. But if that sensor doesn't throw the code than maybe it doesn't matter.

 

[hornsfan10609]

Check your vacuum lines and possibly your intake manifold gaskets. There is a leak somewhere between the MAF and the primary O2 sensor the computer is detecting. Does the port on the side of the valve cover have a hose running to the intake or does it have a little filter on it?

 

[im2bad4ya]

Check your vacuum lines and possibly your intake manifold gaskets. There is a leak somewhere between the MAF and the primary O2 sensor the computer is detecting. Does the port on the side of the valve cover have a hose running to the intake or does it have a little filter on it?

All vac lines are good, getting 20-19 In Hg at idle. Tested my WGA and BOV for leaks and both are good. valve cover has the hose going back into the CAI.

 

[im2bad4ya]

Also, when I removed the head to change the head gasket, I took I left the intake manifold on, so it never came off.

 

[xxskateratxx1]

I had this problem a couple years ago, and ran every test imagineable for all the problems it could be, and replaced everything just to find out that my EGR Valve was stuck open... So i replaced that and it was all good.... But my idle was also pretty low, so im not sure if your experienceing low idle or not but... that was what happend to me...

 

[im2bad4ya]

I had this problem a couple years ago, and ran every test imagineable for all the problems it could be, and replaced everything just to find out that my EGR Valve was stuck open... So i replaced that and it was all good.... But my idle was also pretty low, so im not sure if your experienceing low idle or not but... that was what happend to me...

thanks for the two cents. My idle is good though. I cleaned the EGR last year, it had a lot of carbon build-up.