Another Lean Code Mystery: P0171 & P0174 | Ford Explorer Forums - Serious Explorations

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Another Lean Code Mystery: P0171 & P0174

PsYcHo_FrEkE

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November 2, 2013
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City, State
Georgia
Year, Model & Trim Level
1997 Ford Ranger XLT 4.0L
I'm hoping that I won't get blasted for this since it's been gone over many times, but I'm having trouble with diagnosing P0171 and P0174 codes. The first thing I did of course was reset the codes. The CEL stayed off for a few days then came right back with the same codes... I'm not really having a lot of trouble with power, although it did stall on a hard turn in a parking lot a week or two ago. So far I've checked the voltages on the MAF sensor and cleaned it, sprayed starter fluid around the intake hose (including the one from the oil fill tube), all of the vacuum lines, around the intake and plenum (yes, the seam, too), TB, IACV, EGR (basically anything with a vacuum line attached to it), and tested the fuel pressure. I can't figure out what's causing the lean codes. The only other thing I can think of would be an O2 sensor. I don't have an OBDII scanner with live data, so I'm thinking of running a couple of test leads through the bay up to the top to check the voltages while it's running. Other than that, I'm at a loss. Any suggestions?!

Another note: I did mistakenly clean the MAF using brake cleaner and some q-tips 2 or 3 weeks before the codes came up at the advice of a shop mechanic; however, my voltages are reading spot on so the MAF must still be functioning properly, right?
 



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I'd get some mass air flow sensor cleaner and just spray it good. If it comes back again I'd look at the intake gaskets.

Causes

A code P0171 may mean that one or more of the following has happened:
•The MAF (Mass Air Flow) Sensor is dirty or faulty
Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
•There could be a vacuum leak downstream of the MAF sensor
•Possible cracked vacuum or PCV line/connection
•Faulty or stuck open PCV valve
•Failed or faulty oxygen sensor (bank 1, sensor 1)
•Sticking/plugged or failed fuel injector
•Low fuel pressure (possible plugged/dirty fuel filter!)
•Exhaust leak between engine and first oxygen sensor

Possible Solutions

A lot of times, cleaning the MAF sensor and finding/fixing vacuum leaks fix the problem. If you're on a tight budget, start there, but that may not be the fix for certain. So, possible solutions include:
•Clean the MAF sensor. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
•Inspect all vacuum and PCV hoses, replace/repair as required
•Inspect all hoses and connections in the air intake system
•Inspect and/or test the intake manifold gaskets for leakage
•Check for a dirty fuel filter and proper fuel pressure
•Ideally you'll want to monitor short and long term fuel trims using an advanced scan tool
•If you have access, you may want to run a smoke test
 






+1 on the above, and add a leaky power brake booster.
 






Thanks for the reply. I'll try those and see what happens next. I absolutely hate throwing parts at it without diagnosing the problem specifically (extra work for no reason AND hard on the wallet!) I thought i heard a hissing in the booster once a while back but it went away so I dismissed it as being in my head.

I do occasionally smell fuel as well, but it may be related to a leak I have down by the tank since I only smell it shortly after I fill up. Pretty sure that's either the fill tube crimp ring or the fuel pump gasket.. just been too lazy to check it out. I'm guessing it's the pump gasket since it only seems to leak out when it's over half full, but that's another issue altogether...

I have smelled fuel a time or two when I've put my foot in it, but I haven't found any gas by the injectors. I unfortunately have no experience troubleshooting injectors if it comes down to that...
 






tip: check the easiest stuff first, change the least expensive parts first.
 






tip: check the easiest stuff first, change the least expensive parts first.

I thought this was common sense :scratch:

I get it though... I've met a couple of people that needed to be reminded of that...
 






I thought this was common sense :scratch:

I get it though... I've met a couple of people that needed to be reminded of that...

i certainly should be, but i'm always surprised how many people don't follow it and start tearing stuff apart and/or replacing parts needlessly.
 






i certainly should be, but i'm always surprised how many people don't follow it and start tearing stuff apart and/or replacing parts needlessly.

Common sense isn't as common as you would be led to believe ;)

Bill
 






I used practically a half of can of MAF Cleaner after this conversation. After about 300 miles the CEL came back on (same codes). I guess I'm looking at replacing the intake gaskets. Victor Reinz seems to have the most complete set for about $99 at Autozone or $75 online. It includes practically every gasket on the top end (even injector rings)! I figured while I'm in there I would check my valve lash as well, since it's probably never been checked! Just wish I could find some way to verify that this was the problem before dropping the cash and spending the time. I've done the troubleshooting on everything else, so what else could it possibly be?! *shrugs*

I'm also thinking I would either pick up a couple cans of sea foam deep creep or a few cans of carb cleaner and clean the inside of the intake and plenum but I'm not sure which would work better. Kinda leaning towards the deep creep, but not looking to spend $8 per can. I keep reminding myself that it's not something you have to pull apart often so it's best to do it right (and thoroughly).
 






I used practically a half of can of MAF Cleaner after this conversation. After about 300 miles the CEL came back on (same codes). I guess I'm looking at replacing the intake gaskets. Victor Reinz seems to have the most complete set for about $99 at Autozone or $75 online. It includes practically every gasket on the top end (even injector rings)! I figured while I'm in there I would check my valve lash as well, since it's probably never been checked! Just wish I could find some way to verify that this was the problem before dropping the cash and spending the time. I've done the troubleshooting on everything else, so what else could it possibly be?! *shrugs*

I'm also thinking I would either pick up a couple cans of sea foam deep creep or a few cans of carb cleaner and clean the inside of the intake and plenum but I'm not sure which would work better. Kinda leaning towards the deep creep, but not looking to spend $8 per can. I keep reminding myself that it's not something you have to pull apart often so it's best to do it right (and thoroughly).


Let me know what works - I'm battling the same code as well: replaced the MAF, IAC, and checked the PVC valve/lines. I'm about to order new intake gaskets, but I'm waiting for someone to confirm my suspicion. BOL.
 






Let me know what works - I'm battling the same code as well: replaced the MAF, IAC, and checked the PVC valve/lines. I'm about to order new intake gaskets, but I'm waiting for someone to confirm my suspicion. BOL.

I hope you cleaned the IAC and MAF and checked the voltages before replacing them... Have you tried running down the list jremington59 posted? You can check for vacuum leaks by spraying starter fluid around the hoses, plenum, edges of the intake manifold... just about anywhere air could potentially get in on the top end. I even sprayed my intake tube where the sensors and hoses connect to be sure there were no leaks.
 






I hope you cleaned the IAC and MAF and checked the voltages before replacing them... Have you tried running down the list jremington59 posted? You can check for vacuum leaks by spraying starter fluid around the hoses, plenum, edges of the intake manifold... just about anywhere air could potentially get in on the top end. I even sprayed my intake tube where the sensors and hoses connect to be sure there were no leaks.

Did you spray some starter fluid around the intake when the engine was cold and first started? Unless you have an inspection due soon, or you know for sure it's the intake gaskets I'd probably look at other things. For the cost of the gasket set I'd want to be sure.
 






Did you spray some starter fluid around the intake when the engine was cold and first started? Unless you have an inspection due soon, or you know for sure it's the intake gaskets I'd probably look at other things. For the cost of the gasket set I'd want to be sure.


Yes I did. Used nearly a whole can. It was difficult trying to get any starter fluid down around the intake manifold with the way they bolt everything on top of it, though. I know there are some spots I missed. It also stalled in a parking lot again yesterday... I'm right there with ya on wanting to be sure. That's why I still haven't done anything with it.
 






Okay, so now I have something new going on. After having the engine running at high speed for so long and coming to a sudden stop or after high revs the idle is rough... During this rough idle the headlights dim as well. Eventually it smooths out. It actually stalled on me a couple of times during my delivery route. I honestly think it's just trying not to die... Is this still along the same lines as we were discussing with the IM gaskets or should I be looking somewhere else now?! This may be unrelated but there were a couple of times I thought I smelled a faint smell of burning solder. It only lasted for a second, but I swore I smelled something... That being said I do have a sticking caliper I may have been smelling...

Here's a vid where I tried to reproduce the idle issue. It did do it a little bit. Sorry for the wind noise. The phone was sitting right by the fan...

http://www.youtube.com/watch?v=UydS6Yl8IB0
 






When's the last time you ran some good injector cleaner through it? You might also clean the IAC valve.
 






When's the last time you ran some good injector cleaner through it? You might also clean the IAC valve.

Not sure what you consider good injector cleaner. I put some seafoam in the tank not long ago...

I THOUGHT I had cleaned the IAC before... Starting to wonder if it's going bad... Guess I'll try cleaning it again to be sure... It's funny that you mentioned IAC because that's exactly where my mind went when it started doing this...
 






IAC was dirty... I'll have to remember next time not to assume how long it's been since I did something. I cleaned it up with MAF sensor cleaner (all I had). I warmed the engine and reset the ECU (wanted to see if it would straighten out on it's own before I reset it)... Idle is still dropping too low after coming down from high RPMs... Probably gonna ohm it out tonight or tomorrow.
 






Just checked the resistance using this article for reference: Dead Link Removed

IAC Pins measure 9.4 Ohms across one another

Measuring resistance from each IAC valve pin to the IAC valve case comes up with 0.L on each

I'm a bit confused on this. 9.4 is definitely within the 6.0 to 13.0 range.
Checking resistance between the case and each pin is an effort to see if there is a short against the case inside. 0.L should mean that that there connection (can't think of the right word) and therefore should pass this portion of the test if I understand it correctly; however, the person who posted the article referenced above stated that his was bad because it read 0.L. So... is it good or bad?! LOL
 






0.L (out of limits) means there's an open connection. Bad.

Bill
 



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I feel stupid now for not having double checked that. Anyhow, thanks everyone for all of the help! I'll replace it today and update as to whether or not it's fixed.
 






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