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Weird problem? Help.

4K views 23 replies 6 participants last post by  pzr2874 
#1 ·
So I installed a GFB 50/50 BOV last weekend took it for a ride everything was fine and 1 day later when I was driving home I got CEL got it checked and got code P0171 (too lean) So I checked vac hoses and everything was good, checked MAF sensor and had some crude on it cleaned it up reset the CEL with bat. disconnect light went out, no light driving to work but on my way home I got CEL again?
I also seem to have a very bad lag now. I get to around 100 and it seems like it sputters out??
My guess is the BOV is messing up?
I have it on full recirc. and not vent.
 
#3 ·
Was your BPV gasket good? My tuner also fills the bolt holes with silicone to eliminate all possible leaks around the bolts. Its two things to consider.
 
#6 ·
Now that you mention it the BPV was folded a bit and letting air pass underneath the stock BPV I folded it back and got it as flat as I could till I get another one.

Ill try replacing that or putting some gasket seal on it till I get the new one and see what happens.

The gasket would make it run lean just like that, if so I dont know why it wasnt running lean b4 I bent the gasket back?
sry Im not that well educated in this stuff yet.
 
#4 ·
Even so, that wouldn't cause a lean condition. Really the only thing to cause that is too much ignition advance, too much boost, or something fuel related. I would chock it up to a coincidence after you installed the BPV, personally. How many miles have you clocked? What other mods do you have? Intake? Exhaust? I'm only concerned because my car didn't eve go lean enough to throw a CEL, but it still went lean enough to cause damage. I'm crossing my fingers your car caught it before trouble came.
 
#5 ·
Well the only thing I did recently besides the BOV is the IC hoses and the Inlet hose I noticed alot of crude in the hoses and in the intake itself so I cleaned what I could see out of the intake as well as spray some carb cleaner around the throttle port "not inside just the butterfly valve"

Besides that the only other mod I have done was the K&N intake when I first got the car about a yr ago and didnt have no problems with that after install.

Im running NGk plat at .030
Royal Purple 5w30
93 oct.
To round off the miles on it would be 100k
Thats about all I can think for info on the engine hope this helps a little thanks guys.
 
#7 ·
I'm thinking about it and I don't think a boost leak would make it run lean. More like rich, if it's not getting the right amount of air.

100k miles? Did you do the 90K maintence? Change the timing belt, spark plugs, and flush all the fluids? What is your CEL? The last time my car threw a lean CEL, it was because the front O2 sensor took a shit after my motor swap.

I looked at Impreza Manuals | ken-gilbert.com and under 02-03 manuals. It said the P0171 was a fuel trim malfunction (A/F too lean). Meaning you have too much air and not enough gas. I'd think that would be in the fuel system. Like a crapped out injector, fuel pressure regulator, or crapped out fuel pump. I don't know if i'd drive it too much more and I'd have a trusted tuner or dealership look at it. If you have a trusted tuner....go there first. Because if your car is starved for gas and you drive on it too much or hard. You could really mess the car up; like frying a piston or breaking one.

Edit: I'm still reading the manual. Here are the first Diagnostic steps that a tech would check for both lean and rich fuel trim malfunctions.

1) Check the Exhaust system (repair any leaks, holes, or loose bolts)

2) Check the Intake system (repair any leaks, holes, loose clamps, or disconnection of hose on air intake system)

3) Check fuel pressure (too many damn steps to list...check read this stuff on the DOHC Engine link and its under pdf page 377 and 378)

4) Check engine coolant temperature sensor

5) Check pressure sensor

6) Check intake air temperature sensor.

Man, I'd fix the gasket and go back to stock intake and BPV. If that doesn't fix it...definatly take it in.
 
#8 ·
I assume because you know the spark plug gap is .30, you just recently changed the plugs, and it's not likely the plugs would cause a lean condition anyway, as they are just drones who do what the coils and ECU tell them to. Huge ignition advance or fuel stuff like Kirt is talking about are possibilities, but I also wouldn't be surprised if the A/F sensor was bad. I got mine for around 70-80 bucks on amazon. Basco also gave the excellent advice to only get the Denso one. It's easy to replace too. If you had oil burning through your exhaust due to normal blow-by oil, it could foul the sensor and give you that code too. At least you have a narrow selection for what causes it. . .
 
#9 ·
So today I noticed that the car doesnt start acting up till 3300-4000 rpm mostly in higher gears
4th and 5th gets bad seems like the car on a govener when it gets to a certain speed???
Yeah Ill try the sensors and see if anything comes up.
Is there a way to just take the sensor out and look at it to tell if its bad.
Should I try to seafoam and see if anything gets better?
 
#10 ·
I keep on being "that guy" telling people to open your oil filler cap, and see if it puffs smoke like your breath on a cold morning. My mind keeps diagnosing problems to what my car acted like. . . I don't want to get you nervous, so just open the filler neck and tell us if it smokes.

There's not really a way to tell if a sensor is functioning properly visually. Unless it were missing half of it or something. . . I wouldn't spend money until you know it's not puffing the magic dragon. I just thought of that, and it kind of sounds retarded, but I kept it on here anyway :).
 
#11 ·
I keep on being "that guy" telling people to open your oil filler cap, and see if it puffs smoke like your breath on a cold morning. My mind keeps diagnosing problems to what my car acted like. . . I don't want to get you nervous, so just open the filler neck and tell us if it smokes.
I took the cap off and didnt see any smoke comming out?
Ive been reading alot of forums about this code and from what I have gathered from the way the car is acting and what I have read Im gonna take a shot at a bad MAF sensor.
Being that I have a bigger intake and it being all cruded up with grime when I cleaned it Im assuming it was a bit too late and might have shorted it out or damaged it somehow?
I read the code again just to see what the results would say and one of the results this time was a faulty MAF sensor. So Im gonna take the 130$ gamble and hope that it fixes it.

Ill let you guys know what happens.
 
#15 ·
Yeah I bought some MAF cleaner over the weekend and cleaned it up some more.
Theres a way to test it with a multimeter so Im gonna try that next.

Everytime I reset the ECU the CEL goes out and doesnt come back on till around 38-43 miles of driving????

This is driving me crazy...
 
#16 ·
That's because it's going through a readiness test during that 40 miles or so. Some cars take 80 miles to get there, some take 20. It means the problem's not fixed. Bummer, huh? Anyway, luckily multimeter's are cheap, so that won't be a big deal to test the MAF sensor. Good luck, and I'm stoked to hear that the car was not smoking out the filler neck.
 
#17 ·
Ok, since you didn't answer my question. I checked your profile. You're running a K&N Typhoon Intake. Does it have the heat sheild and are you tuned for it?
 
#18 ·
Sry.
Yeah I got the heat shield and no its not tuned for it but I installed it a while back and never had any probs with it.??

So today I unplugged the MAF sensor while the car was running and surprisingly it stayed running it actually sounded a lil better while ideling Ive read if it runs better with it unplugged that its def. the MAF because your using a different fuel map. So my guess is going to remain the bad MAF sensor. I was gonna try the multimeter test but didnt want to risk breaking something else.

So Im gonna pick up a sensor this weekend and Ill post the results.
 
#19 ·
I have heard someone talking about the same code with the k&n intake...they put a cobb intake on the car and it seemed to solve the problem...and cleaning the maf sensor and putting it back in did you reset the ecu? because these cars have something like corrective learning, so while the car is figuring out the maf again it may not throw up any cel's...
 
#20 · (Edited)
Well, if the MAF theory strikes out. I'd try to get a tune for the intake or get rid of it. The 02-07s really hate the intakes to be switched out without a tune. The 3rd gens can't really run anything either without a tune. But, some of the intakes can be tuned for with OS maps made for them. So, do the homework accordingly.
 
#21 ·
@Baum
I reset the ECU after cleaning it and got CEL again after 40miles.


@Turmic
Yeah I was gonna try to get a tune after I get a DP. I wasn't sure you needed a tune for a intake though I guess what ever mods you do to your engine should get a tune.
Im still learning

I had a 06 that I swapped the intake on it and lost a massive amount of power so ended up putting stock box back on.

Didnt seem to lose any power when I put the K&N on this one though.

Thanks for the pointers Turmic
 
#22 ·
Well picked up the new MAF and installed it and runs like a champ again!
The guy at AZ said that intakes w the oil cones are known for ruining MAF sensors.
Think its about time to invest in a SPT intake.
 
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