P0171 Diagnostic help
 

Hi scoobynet, new member here
I've just bought my first subaru last week, a 2005 impreza wrx300, it has the prodrive pack standard, and a cold air intake, sti injectors, sti tmic, vf35 turbo, decat and a remap by andy forrest to 280bhp and 360bhp depending ding on whether it's on low/high boost.
It had a ecl light when I bought the car, which turned out to be p0171 (system too lean bank 1) I cleaned the maf with maf cleaner and noticed the oring seal was missing, so I fitted a seal and while the fuel economy has improved dramatically the code still returns after about 20 miles. I've used a can of smoke spray and couldn't find any further leaks. Looking good at the graph after a quick drive I don't think it's the front lambda as the short term fuel trim goes 0 when under acceleration. Could anyone be able to help? https://cimg4.ibsrv.net/gimg/www.sco...85cc94e802.jpg

Does it have the standard recirc valve fitted or a dump valve?
if it's got a dump valve fitted it's most likely that causing the problem.

Yeah forgot to mention the dump valve, got a bits dump valve. Do you mean a poor seal or the dump valve itself is faulty?

Put the recirc valve back on mate...dump valves cause more problems than good.
I have seen this code a few times due to dump valves.

Unfortunately I never got the standard recirc valve, is it worth buying a standard one to test it out? The dump valve holds at low boost map (the graph in the pic) but flutters on boost a bit on the high boost map. I've never really heard of this but I've never had a modified turbo car before :lol1: thanks for the help :D

Definitely get a standard valve back on it I'm sure it will fix your problem you will probably notice the car runs smoother aswell.

the trim is supposed to go to zero under boost so that doesn't really give you a good indicator - the code can also be thrown by an exhaust leak at the headers/uppipe so may be worth checking for exhaust leaks too. There should be a decent garage in your area who can perform a proper pressure/smoke test and that will help identify if the dump valve or any of the hoses are leaking on you - smoke alone doesn't always get the job done.

Could be your maf is simply on the way out to be honest ... and as a heads up never clean a maf sensor you can do more harm than good

Lol at 360 bhp from a VF35 that will be an spiked figure its more like 340 bhp just for comment

As has been mentioned normally this is due to an air leak in or around the inlet manifold area or in the intake system after the maf but before the turbo, replacing the seal was a good spot, air could have been leaking in around there and upsetting the maf output, have you checked the filter is still on the end of the cak ? And see if the flexi joint from air intake pipe onto the turbo intake has not split as that would do it. Andy would not have left it like that when mapping so this has happened subsequently
cheers

I've done some fixing, I've replaced the dump valve for a standard recirc valve, and found a small exhaust leak which I've now repaired.
However the short term fuel trim still goes up to +25%, however it goes up gradually over about 9 seconds whereas before it was instantly. But now my long term fuel trim sits at basically 0, fluctuations up to +3% now and again. I don't quite understand how and why the ltft stays at 0 while the stft sits at 25%?

Just pulled a spark plugs, they were unbelievably fouled from running rich, I've ordered new plugs, one stage colder than standard so I will update once the plugs have been fitted to see if it's fixed the problem or not