P0301 code gone! Now code P0171! Please help me!!!

[Hardwareman]

Well my CEL came on a day or two ago and the Ranger has still been running really rough and misfiring occasionally. I "HAD" a misfire cylinder #1 code but I guess I fixed that because it's been gone for about a week now. OR it could actually be that too much fuel is being dumped into the engine. It's still VERY rough at idle when cold but smooths out when warm but still noticeable.

Anyhow, I've now got code P0171. Anyone know where I should start to look? I know I don't have any vaccum leaks because I've thouroughly checked for it. Could a bad 02 sensor make it run this bad even when cold? Like sitting overnight cold? Thanks



Allen

 

[Joelzme]

Wow, that's odd. My understanding of the o2 sensor is that it closes the loop and doesn't really function until it is warmed up. However if it's stuck in closed loop perhaps it wants to run the truck like it is warmed up when it's cold.

Got me man, but hope you get some advice from around here. If you have a fuel/air mixture problem it would seem like it could cause a misfire in one of the cylinders, but I'm not that experienced to know for sure. Doesn't the mixture lean out as the engine gets warmer?

Makes you hate computer senor vehicles!

Found this and it has a few things to check :

http://www.rangerpowersports.com/forum/showthread.php?t=204929

Also found this which is more exactly your problem...hopefully something to check out for ya.

http://www.fordforums.com/f657/ford-ranger-rough-idle-p0301-p0171-126752/

All this makes me think it's not necessarily your PCM tho.

 

[phatcap]

man, i feel your pain. i used to have an '89 mustang 4-banger with the same sort of problems. i never figured it out though and ended up donating it for a tax write-off. at the time my brother was moving out of state and gave me his taurus so i didn't need it anymore...

but yeah, i've been reading your posts and wish i could offer some help but you're more experienced than i (i've never swapped an engine). just wanted to comiserate. that's usually my luck too with cars, if its not one thing, its another. fortunately, my ranger has been treating me well lately (do they have a 'knock on wood" smiley?....oh, i guess not).

anyway, good luck finding out what the real problem is.

 

[bikerboy]

Possible causes
* Air leaks after the MAF sensor, or leaks in the PCV system
* Vehicle running out of fuel or engine oil dip stick not seated
* EGR valve gasket is damaged or leaking around the gasket
* Exhaust leaks before or near where the HO2S is mounted
* Fuel injector(s) not supplying enough fuel
* Fuel system not supplying enough fuel during high fuel demand conditions (e.g., the fuel pump may not supply enough fuel)
* MAF sensor is dirty (can cause PCM to underestimate airflow)


Unplug your MAF and see if the truck runs better without it. If it does then you need a new MAF or you could try to clean it and see if that works. Let us know how it goes and we can try to fix the problem from there but check all those things first.

 

[Hardwareman]

Thank you phatcap, and yes I will further investigate those areas bikerboy.

Thanks for all the ideas. I've driven her quite a bit so far and the light has'nt come back on yet.

If I unplug my MAF while the truck's running the engine dies. I read somewhere that it's normal for it to do that. Make sense?





Allen

 

[bikerboy]

yep that's how it should work. Did you try to clean the MAF sensor? What did you do to get the light back off?

 

[Hardwareman]

yep that's how it should work. Did you try to clean the MAF sensor? What did you do to get the light back off?

You were right about checking those items!

First, I got my CEL light off by erasing the code with a "CAN OBDII" scanner I bought at Harbor Freight.

The problem seemed/seems to be the MAF Sensor. I actually removed the black sensor from the housing and saw that it had crud all over the light bulb looking element thing. I cleaned it off with some carb cleaner I had and then reinstalled it. I coul'nt believe how smooth the engine ran after that! There was no misfiring and my IAC valve, which has'nt worked in ages suddenly began operating normally again. I mean when I unplugged it the engine actually bogged down.

I took it for a test drive and sure enough, there was "PEP" back in the old girl. The engine even compensated for the extra load placed on it by the A/C when I turned it on. I was trying to figure out that probelm forever!

After returning from the test run however i popped open the hood and removed the IAC plug again but this time the engine did'nt bog down. There was no change again. I'm thinking I need to clean the MAF sensor agian or I just flat out need a new one. Thank you for recommending that.




Allen