Fuel Injection Lean?
 

check engine light came on today. SCII says P0171. Haynes manual says fuel injection system lean.

any thoughts?

2000 toyota corolla, i mean, chevy prizm 5 speed.

thanks.

this may be a start
https://www.obd-codes.com/p0171

maybe it will give you some ideas

thanks Beef!

from what i can ascertain from your link:

clean the MAF sensor and check for vacuum leaks downstream. and the sensor may need to be replaced.

Fuel pressure?

Dead injector?

Have you ever cleaned your injectors?

Wiring to an injector?

Lousy O2 sensor?

Lazy fuel pump? Low voltage to fuel pump?

Leak in the exhaust system?

Bob,

everything is running great. mpg is a bit low, but it has been cooler on morning trips. scangauge shows good mpg during the day when temps rise(typical florida winter can be 40F am and 70F at noon). ~37 mpg am and ~43 pm to be specific.

i use amsoil fuel cleaner regularly, but the O2s are new and not OEM.

a toyota tech on another site says a dirty MAF(or one that needs replacing) shows no sign in regard to performance. sounds like my situation.

i did clean it today(MAF), and will add amsoil PI to the next fill-up.

be wary of any additives. an even marginally decent running car shouldn't need anything put in the oil or gas. additives can lead to bad readings and cars can be addicted to them (so to speak)

careful what you use to clean the MAF, anything not specifically made for that job can destroy the MAF

kamesama980,

there's a multi-award winning mechanic here locally that recommends fuel additives, BUT only certain ones. amsoil is one.

and i did use MAF specific cleaner that smelled suspiciously like brake cleaner. i wonder if i could have saved a few bucks going that avenue instead?

Brake fluid? I can imagine them smelling like brake cleaner, because non-chlorinated "ABS sensor safe" brake cleaner is safe on them as is any "electrical contact cleaner" as is isopropyl alcohol.

yup, brake cleaner, not fluid, thanks. it's been edited.

i've cleaned the MAF sensor twice, and the FI lean code has come back twice. after resetting the code, it takes between half and 1/4 tank to come back.

looks like i'll be headed to NAPA soon.

would any like to speculate if this could lower FE? again, i've been a bit low, but each of the recent tanks have had some near freezing mornings.

depends, some cars if the idiot light comes on the computer goes into some default setting that typically isnt the best, some ignore that sensor and adjust according to other sensors.

but all in all prolly best to fix it. as if it really goes out it can cause loads of weird issues

also check your vacuum lines, if tier cracked or leave black marks on your hand replace them ALL. thier dry rotting and most likely leaking

filled up today and i dipped below 40mpg. aside from a few extra city miles, nothing noteworthy except the check engine light. in fact, prolly warmer temps than the last few tanks.

maybe that MAF sensor does need replacing. there are no detectable vacuum leaks.

On my 92 Nissan, my injectors fail about every 4-5 years (1 year warranty on replacements). When I notice a rough idle (but not yet a regular miss) and a little lack of power on the interstate I get out my digital multimeter and unplug all 4 injectors and check the resistance between the contacts. I'll spot one with 3 times the resistance values as the rest and I'll replace it and all will be well for a year or so until the next one gives out...

I assume the bad injector doesn't inject as much fuel as it should and thus the oxygen sensor likely sees a lean condition. I have OBD0 so I don't get a CEL or code.

Comparing the resistance of the injectors shouldn't take but 5 minutes and would eliminate an electrical failure in one of them (but would tell you nothing about if one was clogged).