LowTec MOHawk

hey guys i got a 2000 civic with dtc p0171 (fuel system too lean). this car is completly stock with no mods keep in mind. this is what i got so far

short term fuel trim always about 1.22
long term fuel trim always about 1.15-1.22
fuel press 35psi idle 45psi regulator hose off
fuel vol 1/2 quart in 15 seconds
no cracks in exhaust before the primary HO2S
HO2S is working properly and non biased lean
map value of .92v
monitoring of the HO2S shows a lean misfire
spark lines are 13kv idle and 18kv under snap (i assume its high cuz its running super lean
visual inspection of injectors and rail dont show n e signs of debris or clogging and the little filters are clean
pcm is good (substituted a known good unint)

well i now im stuck and cant think of n e thing else it could be..............please n e body out there that knows of anything else that could cause a lean condition like this??? im going outta my mind on this one

MasterKwan

Is the O2 sensor crossing .5 volts or is it stuck at a specific voltage?

Page 11-164 in the manual. P0171

Fuel pump
Fuel Feed line
Filter clogged
Injectors clogged
O2 sensor
MAP sensor
EGR (D16Y5)
Valve clearance
Exhaust leak.

I'd follow the trouble-shooting procedure in the manual. First they test fuel pressure, then O2 sensor.

Hmm disconnect and plug the evap canister vacuum line. They say it could be leaking.

LowTec MOHawk

no the o2 cycles and ill try eliminating the canister out of it. but id think that that would cause a rich conditon.......i mean i could be wrong but the canister stores the HC's and releases them though the purge valve right? i checked for the duty cycle of the purge vavle on the data list and it was at 0% so i dont think its the evap. but **** ill try n e thing at this point. lol thanks alot man

LowTec MOHawk

bump n e one else have n e ideas?

MasterKwan

Maybe you should get the manual and follow the test procedure. That's what I'd do.

LowTec MOHawk

i have a factory manual. ive checked for any and all bullitens, service news and tech-line summary's. the manual did not lead to an answer. there are no bullitens and the one service news that was available was just about the enable criteria of the code P0171...........

MasterKwan

It's not clear, you ran through the entire test procedure that starts on page 11-164?

I assume you've swapped out the primary O2 sensor for a known good one?

I find your symptoms to be kind of contradictory. It doesn't sound like the ECU really think's it's lean. I'd expect the fuel trim to start out around zero and then move rich as the ECU tries to adjust for what it thinks is a lean mixture.

fmrprojects

i would say clogged fuel filter, vacumm leak, bad fuel pump

LowTec MOHawk

yup went through every test thats in the manual and yes swaped the o2 for a good one
the only thing i cant see and havent done is checked the actual spray pattern of the injectors. i dont have an injector tester to bench test them. and the volume check and pressure check eliminated the fuel filter and fuel pump as possibilities, and a vacuum leak isnt the issue considering the MAP was at .92 volts..........

MasterKwan

Well, the test procedure should have proven the map's good. Just for grins, I might hook up a wideband and see if it's really lean or not. I know that's not something most people have in their toolbox.

After you clear the code, how long does it take before it comes back?

jdeemseerx

what do your plugs and ignition system look like.. something else to check out

crxmadness

im bringing this one back from the dead because i have the same and the same problem. i have also check everything that has been mentioned and my readings are pretty consistant with the original poster except my short term fuel trim is +25 and i dont have a lean misfire. i sent him a pm but i really need some help.

crxmadness

Anybody have any ideas?

thesmogman

I would add some propane to it just to see it go rich to lean. Watch your fuel trim step the other way while watching the O2 voltages. Kind of a manual check for piece of mind.

Your ECU is thinking lean because it stepped rich. So this is good. You are right on the ecu's limits thus throwing the code.

Map @ .92 with the engine running is 20in.hg. My first thought was it is a little low but it is about right. I am sure you checked it with the motor off too.

You might have a small vacuum leak check all vac. hoses and valves, PCV and your brake booster's check valve. It would be a small leak, could be your iacv too.

Did you detect the misfire in only one cyl? Or across the board. If it is one cyl look at all hoses closest to the missed cyl. Inspect the IM and the gasket too.

But before I go I just thought of something else. Have you looked at your temps both air and water? That could be another reason it might be screwing up!

There is a couple for you to check.

crxmadness

Thanks for the input, ill post what my results are.