Hey guys, I'm trying to find the problem I have with my lancer before I sell it to some one else. I would hate to sell a car with a problem...

Anyway p0171 is the system too lean code. I have a bluetooth reader that allows me to read plenty of info and active data.
From what I can tell, the STFT is within 3% +/-
The LTFT is 12.5% and lately it has been between 12.5% and 15%.
Vacuum pressure at idle is -18psi and when I rev to 2k rpms is goes to -22psi then of course when I drive it and go WOT it goes to 0psi

I have done the following so far:
- cleaned the mass air flow sensor
- changed the exhaust gasket between the first o2 sensor and the cat
- sprayed the vacuum lines and manifold with carb/choke cleaner
- reseated the stock air box
- changed air filter ensuring air box was correct again
- New spark plugs installed (NGK #2687) .032 gap
- sprayed carb/choke cleaner on each fuel injector


The p0171 will stay on for the day and go back off for a week or two. I especially hate it because I think I have fixed it finally and then bam, in my face again lol.

What do you guys think?
Does the vacuum pressure at -18psi concern anyone? From my experience it should be the highest vacuum at idle and gradually less when the throttle is pressed.
My only thoughts are clogged injectors, bad fuel pump or filter, or a solenoid is not closing allowing pressure at idle to be lower.
Of course my main concern and the reason for the code I believe is the LTFT being +12.5% consistently.


In case this has something to do with something lol. When I fill up the tank I get about $5 in before it clicks off, it keeps doing it until it's full. I know I need a vapor canister replacement. I believe the previous owner was overfilling on a regular basis which ruins the charcoal canister.

 

This code has been haunting me for the longest time. I'm pretty sure I'm in the same position that you are. I've done almost everything you have except change the gasket in the exhaust. At this point I have to believe it has something to do with our fuel system. I'm trying to get this fixed in the next couple of weeks to pass smog. Let me know if you make any progress.

Oh and the other thing I did was change the front O2 sensor and change between 87-89-91 octane over the course of a couple weeks. No help.

 

Thanks for the input, I was sure I was alone on this one. I'll keep posting my updates here.


I've been running 93 octane since I got the car last year. The car sounded good intake wise for a couple months until I realized the under side of the air box was unclipped. Now it sounds like a normal stock running car with no intake noise lol. It was after it was put back correctly that the light popped on.


Anyway yesterday I noticed the STFT when the SES light was on is bouncing between 10 and 15% at idle. I added a thing of super concentrated injector cleaner and filled the tank with 91 octane straight gas (instead of with 10% ethanol). Today the CEL turned off (again) and the STFT is hanging out at 0% for about 15 seconds, then creeps towards the 10% before it settles at 3-5%.

Basically when I'm cruising STFT is fine at -5 and +5% and LTFT is at 5%. It's only when I decel that the LTFT goes to +12.5%.

Would an evoscan test run help anyone looking at this?

I am going to try a new front o2 sensor. $40 will help me rule this out and make sure the numbers are good.

 

Using an app called "Torque pro" for android paired with a bluetooth OBD2 live feed scanner:


This is at idle:


Under Acceleration:


At Idle again (notice STFT is much higher now):


During a cruise at 60mph (which these reading's are acceptable even the LTFT, which is why I believe the SES light goes back off):



Every thing tells me vacuum leak, but nothing I spray makes the car rev. I'll try plugging hoses later to see if we get more vacuum over the scanner.


EDIT:
On the mazda forums it looks like I may have a bad purge solenoid valve.
http://www.mazda***********.org/foru...-fault-119540/

 

Before I go and order a purge solenoid...

Is it possible a fuel pump that you can hear a whine from outside of the car (stock FP) would indicate the fuel pump is going bad, possibly causing lower pressure at idle therefore lean condition at idle?

I know it's louder than normal because I have another 2008 lancer 5spd that I can start and not hear the whine. Both cars have a full tank of gas. I'm just looking for re-assurance on this last suggestion.

 

Yea, I'm having the same type of problem. Everything is all out of whack at idle and low speed, but when it all warms up and I start driving, it's all smooth again. Another reason I think it might be the fuel pump is because I'm not having the same mpg problems that most people get with the p0171. Instead I'm actually getting better mpg which would make sense if the fuel system isn't working correctly and the car reads lean. I also don't have any noticable problems. The only real issue I get is when I start the car or during colder starts (it's 110 degrees out here in Vegas lol) it seems to struggle to keep the rpms up and will often oscillate between 600-900rpms. Other than that, when I start driving everything is back to normal. I'm thinking that I'm losing pressure overnight or as the car sits? Are you having the same issues?I guess a fuel pressure test would help, but it has to be when the car is cold which is a bit more difficult...

 

I'm right there with you guys. My GTS is pretty much stock aside from an AEM SRI. Just started getting the code a couple months back and it goes away after a couple trips. Hard to determine what's going on when it's so intermittent

 

Depending on where the vacuum sensor is in the system, at idle you would have highest vacuum and it drops as you go up in RPMs. That is typical of a manifold absolute pressure reading.

Other vacuum ports will give least vacuum at idle and build as RPMs build.

This may help guide you in where to look for a leak (if you have one).