aspork42

Sorry if this has been addressed, I can't find it in a search...

So the root of my problem is error code p0171 - "fuel system too lean" that the car threw after an oil change... I've done a lot of reading on this site and many others on the net. Yes, I know there are many ways the engine can run lean - bad O2 sensors, vacuum leaks, and other sensor malfunctions.

I can't seem to be able to locate a MAF sensor on my 2005 civic (1.7l lx coupe) to clean or test.
From what I've read (and asking to buy one at the store) is that there isn't one. Does the engine read from the IAT (intake air temp) and MAP (manifold absolute pressure) sensors to know how much air came in?

I'm thinking that a dirty MAF would cause the lean code, but I can't find one...

* side notes follow below - I'm mostly just looking to know if we have a MAF *

(I have a Craftsman scanner - my Short term fuel trim is in the 30's when it should be around 0. I'm reading ~.3v (lean) on the first 02 and ~.8v (rich) on the second after the cat... is this normal that they would read that far different? why would the downstream be richer than the first? I've already tested 02s, IAT and MAP sensors. Engine pulls good vacuum from idle on up. Fuel pressure tester is on-order for bad pump/filter. Only other thing I haven't done is look for vac. leaks by spraying something flammable around the engine bay and I'm not too keen on that idea...)

02civicsi02

Yes you have a MAF sensor. MAF sensor is short for mass air flow sensor.
Usually when your car runs lean there is a change in the air/fuel ratio.

lazlong

It's either gonna be your primary O2 sensor(1), valve clearance, injectors, or EVAP canister purge valve.

Did you check primary O2 sensor output while it was running?

As quoted from the service manual: "Is the output less than 0.3V or more than 0.6V?

YES- replace the primary O2 sensor

No- Go to step 4

aspork42

A+ on posting that image. Yes, the EVAP solenoid holds good vacuum (like 10 inHg for 10 minutes until I unhooked it)
The primary O2 was reading ~.297v and would go to ~.5v momentarily when I blip the throttle (read directly off the sensor wires).

So if there is in fact a MAF, could someone please post an image or a link to an image? For the life of me, I can’t find one. I’ve pulled the one on my 96 firebird for reference. The only connection on any of the Honda’s airbox assemblies is the IAT that plugs in past the air filter, almost directly above the throttle body. The rest of the sensors/solenoids are past the throttle body (idle air control, MAP, EVAP solenoid). I have pulled out all the airbox components and found nothing.

The car still purrs like a kitten and runs like the day it was new. This problem came up right after an oil change... I think I need to start spraying flammables around the engine compartment in hopes to find a vacuum leak...

lazlong

There is no MAF on our cars. You could try replacing #8: http://www.bkhondaparts.com/billkay/...itch=&hidIrno=

02civicsi02

Ya on further investigation you dont have a MAF sensor, the 8th gen civics have a MAF sensor.

aspork42

The Purge sol. holds pressure. I think the Primary O2 is bad...

How strict is the <3v and > 6v rule for the O2 sensor?
I was reading about .28-.29. I could blip the throttle and get up to .5v, but it would always settle down to <3. It wouldn’t really change when the fan was running or not.

gearbox

iTrader: (95)

01-05 civic has MAP (manifold absolute pressure) sensor.

lazlong

Don't know. I'd hate to tell ya yes and have you waste $250 on a sensor.

lazlong

Ok, your O2 sensor is fine.

You need to check for vacuum leaks again. 90% of the time it's a vacuum leak. With the car cold, hook up the scan tool and put it to read the O2 sensor output again. Take off the airbox and CAREFULLY spray each vacuum line with carb cleaner and look for a change in the sensor output or listen for the engine to rev. the reason you do it while the engine is still cold is the lines will swell and close the leak when they warm up.

If no leak, replace the purge valve.