Fault code P0171 on Subaru Impreza WRX 2003
 

Hi guys, first of all, I am running on LPG on my Subaru, it's been professionally fitted but the check engine light is constantly on. I bought an OBDII scanner and it reads a fault code P0171 System too lean (Bank 1). I was advised that the O2 sensor detects too much air or it can be an exhaust leak, probably a fault with the catalyser? Since I bought the car, the intake pipe leading to the air filter had a hole and it is covered with thick tape, so if I replace the pipe do you think this would solve the problem, or do you know of anything else that might be causing the fault? Thanks in advance! :)

Not a cat fault as that's a completely different code. If its post maf where you have the hole in the pipe then you will be drawing un-metered air into the engine which will cause it to run lean

Thanks for the answer mate, I will replace the pipe as soon as possible and will see if it will come on again after I clear the fault.

I also checked the fuel system status just now, it says: "Closed loop, using O2 sensor for fuel mix", is that how it's supposed to be? A friend of mine suggested to look at the AFR rate, he said on boost it doesn't have to go down below 12, normally it's 14.5-15, otherwise if it is below 12 that causes the system to be lean. BUT I can't find and add the AFR display, he said it might be because the WRX back sensor is not wideband like on the STi?

Defiantly the intake pipe i had the same problem and my car would bog low revs and had the same code . The intake pipe was ripped badly at the turbo inlet . So I fitted a silicone intake and it solved it . Cars smoother and doesn't bog

Thanks for the replies guys, that is how my pipe looks like:

https://fbcdn-sphotos-c-a.akamaihd.n...3451e7891c8f01

One of my mechanics told me that because it's got tape over it, the problem is not the pipe, so he guesses it's the lambda sensor that needs changing.. However, I am struggling to find a pipe like this..

Clear code, drive on petrol and see what happens, than You will get closer to answer is lpg map problem or air

Right, I replaced the intake pipe today with a new one, cleared the code and after about 10 miles the light came on again. I was driving on lpg. I am thinking, it could be the lambda sensor that's playing up..

Using the obd reader it should tell you how much fuel is being added or taken away over short term and long term fuelling. Measure these, post them up and will see what u get.

Your maf sensor could be reading faulty at idle which is very common, effects fuelling, causes a code to be logged and engine light to illuminate.

If you've gotta a mate with a scooby easy way to check is record/write down obd readings, install mates maf sensor on your car, record readings and compare them. My money on maf sensor.

Turn off the LPG and run on gas, clear the code and then see if it comes back, I think you have a problem with your LPG install, I have mapped several cars that have been fitted with this type of system and they can have problems like this.

bob

Thanks for the replies guys, yes it's definitely the LPG, I ran it on 100 octane for a little while and it came off, then came on again on LPG. I heard the lpg in the UK is lower octane than that in Europe, on the continent they put some additives to boost the octane. The system was installed in Bulgaria by a qualified installer and had no problems across Europe and as soon as I put lpg here the light came on. So I bought a Lovato cable with software and he'll try to see what's wrong with the map via team viewer :lol1::lol1: I was refused a service by an lpg technician here because apparently he won't touch someone else work.. ridiculous.. Anyway, the car runs smooth, there's no loss in power and fuel consumption is just the same, I am very happy with the lpg as there is a minimal difference.