Engine codes come and go: P0457 and P0172.
2004 Subaru wrx sti 85K miles. 6 spd
- when I’m accelerating somewhat faster at about 4K RPM my engine starts sputtering and acceleration slows down. It also struggles to start when car is warmed up, and cold start isn’t a problem. It also smells of gas. I know I’m running a bit rich
Those codes are for the EVAP system and vacuum leak. to diagnose correctly, you need a mechanic to analyze the data. Based on the symptoms you got, I would start with pressure testing the fuel line.
"Running a bit rich" is an understatement. The computer triggered the P0172 code because (using AFR sensor (O2B1S1) voltage values)), it can't overcome the rich condition by adjusting (negative) fuel trim and it's at its limit to maintain the 14.7 parts air to 1 part fuel ratio. (when the code is triggered)
When that code is getting triggered your Negative Long Term Fuel Trim must be pegged. (you'd think that would raise any mechanic's eyebrow).
You're running very rich and with your turbo setup the first place to look is for a Boost Leak.
Think about it. When a Vacuum leak occurs, unmetered air (after the MAF/MAP sensor(s)) is getting into the intake manifold.
(The computer doesn't know it's there so it can't add the appropriate fuel, and a "Lean Condition results).
With a Boost Leak, the air has been "metered". The computer expects it to enter the intake manifold and adds the appropriate amount of fuel for that "metered" air to maintain the aforementioned 14.7 parts air to 1 part fuel ratio.
But if you have a Boost Leak. The "metered" air never gets into the intake manifold. (it's leaking out before that)
The computer is adding fuel for air that never makes it to the combustion chambers.
Meanwhile, the AFR (O2B1S1) sensor is telling the computer (which "thinks" it's adding the correct amount of fuel based on the MAF/MAP sensor metered air) that the mixture is too rich.
The computer "believes its sensors at the air intake and exhaust. It has no way of knowing about any Boost Leak so it drops the P0172 code in your lap and "says", you figure it out.
Since you mentioned mechanics I'll assume you aren't a "Do It Yourselfer".
Most shops (that do a Boost Leak Test) will either use smoke, or more likely low air pressure to find any Boost Leaks.
You may want to call around your area and ask a few shops if they can perform a Boost Leak Test on your Subaru wrx sti
I have a maf delete.. I have a data logs but I can’t upload them on here
You still use the MAP sensor and the IAT sensor to calculate air volume going into the intake manifold and the computer uses those inputs to adjust injector pulse width. (fuel trim)
So if you have a Boost Leak, the "calculated air" never makes it into the cylinders and you'll have too much fuel being added to the combustion mixture. . (Running rich)
I have a maf delete.
That's the reason.
