1999 Mitsubishi Eclipse P0171 code is haunting me

Has anyone checked for a vacuum leak? Have you checked fuel pump pressure to make sure it isn't weak?

check your fuel pressure with a gauge if non turbo it should be 47-50 psi with key on engine off and if turbo should be 33psi @ idle. Also check for a vacuum leak use choke cleaner and spray around intake if rpm changes you found it.

no leaks and pump is brand new and properly installed. double checked that

Read this for more info:

https://www.2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers

Let us know what you find.

Best, Ken

Did all that but still no luck

check connections at O2 sensor as well as ecm . I t may be a bad ecm unless your mechanic did a freeze frame and checked all the figures for being correct.

how would you go about checking the ecm

check everything else first and then see if ecm is sending a signal out and return

Sorry I haven't gotten back because I was on a business trip. The car runs great the only problem is the light. I was thinking could it be possible that the ecm may be stuck on that code.

if an ecm "gets stuck" then the problem is the ecm or a connection. If everything checks out to the ecm and the light still I s lit then its' got to be the ecm. the only thing I can think of her eis that fuel pressure should be48-51 w/o vacuum at idle unless this is a turbo which should be 42-45 w/o vacuum at idle. Unless it's a vacuum leak at intake etc. try spraying choke cleaner around intake to see if idle changes. If it does I tmay be leaking vacuum. Other than that I cannot give any other suggestions.

thanks for all your help

I am getting this code. I have done everything the code says and the light is still on. The only thing I noticed is that it has a very rough idle when in the stop lights. The car sounds like it is sputtering and when I get out the car has a smell of gas from the exhaust. Another thing is that it acts like it wants to die out sometimes. These are the things I have changed:

oil change and filter
O2 sensors
PVC
PVC valve hoses
vacuum hoses
spark plugs and wires
fuel filter
fuel pressure regulator
put a fuel injector cleaner in the tank
fuel pump
air filter
coolant temperature sensor
idle control valve


any help would be great
Thanks in advance

check fuel pressure with a gauge first. see pic for causes it may be temp sensor or anO2 sensor if you got a bosch one those are not very good also check for an air leak through duct work leading to throttle then check sensors with chart I'm sending.

Thank you will do this in the morning

Thank you very much. This really helped a lot. What turned out to be was the brake booster vacuum hose. Replaced and car is running smooth again. Tiny vibration on steering wheel but it is not failing out on me. If you got any idea what that might be let me know. Thanks again

vibration can be anything for exhaust hitting body to tires have it check locally

thanks I will check it out

Computer problem
2003 Mitsubishi Eclipse 4 cyl Front Wheel Drive Automatic 102000 miles

what is wrong with the car when it has these two codes po 171 and po 300?

P0171/P0300 random misfire

A lean fuel condition can be caused by:

* Low fuel pressure due to a weak pump or leaky fuel pressure regulator. (use a fuel pressure gauge to check fuel pressure at idle)

* Dirty fuel injectors. (try cleaning the injectors)

* Vacuum leaks at the intake manifold, vacuum hose connections or throttle body. (Use a vacuum gauge to check for low intake vacuum)

* Leaky EGR valve. (Check operation of EGR valve)

* Leaky PCV Valve or hose. (Check valve and hose connections)

* Dirty or defective Mass Airflow Sensor (MAF). (Try cleaning the MAF sensor wires or filament with aerosol electronics cleaner. Do NOT use anything else to clean the sensor, and do not touch the sensor wires)

I am getting this code. I have done some work to the car but the light is still on. the only thing i noticed differently is that it has a rough idle when in the stop lights. some times when i get out the car has a smell of gas. These are the things i have changed:

O2 sensor
pcv
pcv valve hoses
spark plugs and wires
fuel filter
fuel pressure regulator
put a fuel injector cleaner


any help would be great
Thanks in advance

Often times, a lean mixture is the result of a vacuum leak. Have you checked that? Also, have you confirmed that the fuel pressure is within the manufacturer's specs? The sensor you replaced, was it the front heated O2 sensor? Are there any exhaust leaks? Have you tried cleaning the MAF sensor with the proper product?

I changed both o2 sensors. There is no maf but I did clean the throttle body very well. The spark plugs that I took out were black. I have checked all hoses and they are new. The exhaust system is completely new and the gaskets are well placed. I doubled checked that. The mechanic told me that the fuel pressure is fine. The old fuel filter and the regulator seemed plugged.