P0171 - System to lean (Bank 1)

[baldacchino]

Hi All,
I have a MY07 liberty wagon with 34 000km on it, 100% stock.

Over the long weekend I threw a P0171. After resetting this it happened again after 20km, and then again after another 20km.
Thus far all I have done is cleaned the MAF, given all the vacum hoses a good looking over, put in a tank of 98 octane fuel and given it a good hard run.

What I am noticing it is struggling to maintain idle when cold and it some times hesitates when accellerating.

Subaru want to ultrasonically clean the injectors, a company who builds Subaru race engines are suggesting an additive.

Any ideas guys on what the issue could be. I was thinking of changing plugs incase of a weak spark.

Shane

[Robbks]

start with plugs.
a mis-fire can read as a false lean condition when tuning (as the unburned oxygen is seen by the o2 sensors)

but it may need an injector clean of some description.
there is a good purge that can be done whereby they run the car for 30 minutes on the purging solution and disable your fuel system. this procedure DOES work well.

[baldacchino]

Thanks for the reply.

All seem easy enough. Well this is my next question. I am not foreign to engines but these boxer engines seem harder to work on than a modern japanese sports bike.

How do I get to the plugs out on these 2.5i engines. Does anyone have a walk through or a link to a service manual?

Shane

[Dropz]

I've found at work this is a common fault on these, normally you can just clear the code and it's fine, but if that doesn't work we replace the front o2 sensor in the cat.

Plugs, passenger side you can get to with everything in, but the drivers side you need to unplug the afm, take the back of the air box out and the pipe upto the damper air box, then you should be able to reach them fine. I use this combo; 16mm spark plug socket, short 3/8ths extension, universal attachment, long (~300mm) 3/8ths extension, 3/8ths ratchet. That way its nice and easy to reach as your not jamming your hands down between the engine and chassis rail.

[baldacchino]

Thanks Dropz,

Any specific plugs I should buy, or should I just got to SuperCheap and get some Bosch or NGK plugs. I guess I am asking should I go Irridium and whats the gap level (If anyone can provide a link to a service book, it probably would stop my easy questions)?

O2 sensors are expensive, I think close to $300 for this car on eBay. Is there a way to test this.

If this was your veichle what would you do in what order.
All I have done is the MAF.

Forgot to mention, in all cases this light has come on when the engine is very lightly loaded, 80km/hr in 4th flat ground.

Shane

[Dropz]

I would pull the front o2 sensor out and clean it, as well as change the plugs.

Iridium aren't necessary, but personally I would just for performance reasons. From memory the gap is 0.8. Not 100% on that, the genuine plugs at work are pre-gapped to specs so we don't often check them, only a few guys do.

We test the operation through a computer, but simply all you need to do is check the voltage output of the sensor. Run the car to operating temperature, unplug the sensor and connect a voltmeter to the sensor plug, snap the throttle and watch the voltage readings. low voltage (~0.2V) is a lean mixture, high voltage (~0.9V) is a rich mixture, so once you come off the throttle it should jump to rich, when you first snap the throttle it should be lean. Other ways to control the mixture slightly you can remove a vac line (such as the one on the passenger side of the throttle body) to make a lean mixture or spray/tip/squirt some fuel into the intake to make a rich mixture.

[Robbks]

I would pull the front o2 sensor out and clean it, as well as change the plugs.

Iridium aren't necessary, but personally I would just for performance reasons. From memory the gap is 0.8. Not 100% on that, the genuine plugs at work are pre-gapped to specs so we don't often check them, only a few guys do.

Iridiums aren't necessary and provide no real perfomance benefits.
I assume you have a 2.5 NA?
If so Standard $3 NGK plugs are fine. BKR6E-11
1.1mm gap for NA's, (0.8mm for turbo)

as for o2 sensor, cleaning them hardly makes any difference, and with so few KM on it, i wouldn't think it's dead yet.

quite possible it's an exhaust or intake leak on that side of the engine.
if you've got a vacuum line off somewhere it'll rubn lean and won;t idle properly

dirtry fuel filter could also be the issue (coming up to 40,000km it will need one)

[tangcla]

there is a good purge that can be done whereby they run the car for 30 minutes on the purging solution and disable your fuel system. this procedure DOES work well.

Is this the equivalent of a NOS purge? Will it give me more horsepower?

[Robbks]

there is a good purge that can be done whereby they run the car for 30 minutes on the purging solution and disable your fuel system. this procedure DOES work well.

Is this the equivalent of a NOS purge? Will it give me more horsepower?

hahahahaha.. to much F&F for you

restores your lost HP,
it basically works as a concentrated version of in-tank injector cleans, so it gets the spray pattern and atomisation back to it's optimum condition without having to pull the injectors to be cleaned.
it also de-carbonises the valves/ seats, etc as using a can of upper-engine cleaner would.

it's a filthy job to do without good exhaust extraction

[baldacchino]

Hi Guys,

Still not to clear on this purge.

I was going to try tonight changing the plugs with the standard platnium plugs and running an in tank fuel injector cleaner. Can a brand or product be suggested?


I beleive I have looked for vacum hoses coming off and can't see anything. This issue takes like 30km of driving to present itself. If a vacum hose was the problem, wouldnt this be near instant?

Shane

[baldacchino]

Also, I purchased an ELM327 (should arrive this week). Does anyone have any software recommendations.
The link below has a list of software compatabile with this device - http://scantool.imechatronics.com/downloads.htm, nothing like personal recommendations.

[Dropz]

If the problem takes some driving to occur then it is only present when the vehicle is hot.

Subaru have a fuel additive available, also if you want to clean carbon and crap from inside the engine try Amsoil Powerfoam. It's stronger than the Subaru Upper Engine Cleaner.

[baldacchino]

Okay an update.

I called in at Subaru in Mentone last night and was having a chat to the service manager. He asked me if this occuring when the veichle is in cruise. Sure enough it is. This light only comes on when the veichle has cruise enabled. The car supposedly goes in to a closed loop scenario when this happens.

Does this help anyone to help me diagnose the issue.

To date all that is done is a tank of 98 RON and fuel injector cleaner, the car seems much much happier with perfect idling. Kind of hoping when I get my elm327 and I reset the code it doesnt come back. Still planning to do plugs.

Shane

[Robbks]

he meant in cruising conditions, i.e Light to medium throttle.
as opposed tio when cruise control is being used.

this is called Closed Loop Fuelling
the ECU monitors the o2 sensors and adjusts fuelling accordingly.

when you're accelerating more heavily, the car ignores the o2 sensors and just pumps in fuel according to the MAP/ MAF/ TPS voltages and engine rpm conditions.
This is called Open Loop Fuelling

[baldacchino]

Based on this then could it be the O2 sensor in the manifold?

What would you suggest I look at?