P0171/P0174 Mass Air Flow sensor nightmare

[brian1269]

I have been reading quite a bit in the forum since my truck starting having problems and thought I would post my situation in case anyone has any ideas how to help.

I have a 2001 Ranger 4.0 and a few weeks ago my check engine light came on and was giving the P0171 (System Too Lean Bank 1) and P0174 (System Too Lean Bank 2) trouble codes.

Loss of power, rough idling (including dying) and rough running all started and have gotten worse and worse.

I have read quite a bit in this forum about people having the same problems and it seems most point to the Mass Air Flow sensor as the culprit. So today I removed it, cleaned it with CRC MAV sensor cleaner, put it back in and nothing changed. All the previous mentioned symptoms were still there.

I also read a suggestion on another site that said to test the MAV sensor you can disconnect the wire harness and run the engine without it. Supposedly this causes airflow to be inferred by using rpm and throttle position instead of reading the MAF sensor. It says that if the lean driveability symptoms go away, the MAF sensor is probably contaminated and should be replaced. If the lean driveability symptoms do not go away the MAF sensor is probably not contaminated.

OK so I disconnected the wire harness and started it up and all the symptoms went away immediately. As soon as I reconnected the harness all the symptoms returned immediately. I was optimistic I had found the problem since I had already cleaned it so I figured it must have gone bad. What else could it be right? So I got a new sensor, installed it, cleared the trouble codes and started it up. To my surprise all the lean symptoms were still there. I drove 15-20 miles just to make sure but no change, and the check engine light came back on.

So now I am really discouraged. Does anyone have an explanation for this, or have an idea what in the world the problem could be?

 

[scalrngr]

Mine had those same codes a while back and it turned out to be a vacuum leak. The fuel rail to intake gasket was bad. I have heard of other bad engine gaskets causing these codes too.

 

[np205]

I had a vacuum leak also that did it. EGR pipe to the intake manifold.

 

[shadetree]

Make sure the gas filter is clean. Take it off, and if you can blow thru it easily, it's probably ok. If you have to blow hard to get air thru it, it is plugged up. Make sure there is sufficient fuel pressure. Pump could be getting weak. shady

 

[MAKG]

Vacuum leaks (as mentioned), multiple exhaust leaks (fairly unlikely, but not at all impossible), and poor PCM or body grounds can also cause both of these codes.

 

[brian1269]

The thing I can't figure out is why when I disconnected the MAV sensor why did the lean running symptoms go away? Then when I connected it again, they all returned. I am really confused why putting in a new MAV sensor didn't fix it.

BTW, I thought it might be the fuel filter also because it hadn't been replaced and my truck has 51,000 miles on it, so that was the first thing I tried.

 

[copperranger]

I have a 99 ranger and i have the same problems. It dies when i start it at least once every time. I just hold the gas down for a couple seconds and it seems to go away kind of. I just tried pulling off the harness and it would barely run. What else should i try? filter has 10K on it, new plugs and wires. New O2 censors, cleaned the MAF. Was thinking the injectors are bad. Theyre 170K old

 

[fordwheelinman]

When you unplugged the MAF, the unmetered air coming in through a vacuum leak (possible cause) would be casing RPM diferences, when the computer goes into "inference mode" so to speak, it would be able to compensate with fuel based on other sensor readings. When you plugged it back up, its getting a direct signal of metered air, and fueling the engine according to that. This could explain why you had the symptoms after replacing the sensor.

 

[copperranger]

is there another way to check for vacuum leaks other than just taking it in for diagnostics. i'm on a pretty limited budget right now

 

[Big Jim M]

Yep! A can pf carb cleaner sprayed in places where you suspect a vac leak...while the engine is running..if the engine sppeds up or smoths out..you have found a leak.
Big Jim

 

[copperranger]

i heard that and i found a can of starter fluid that i use for my snowmobile and i sprayed it around some places and nothing happened. Parts that i could see anyway.

 

[wahlstrom1]

Try right around where the fuel rail sits, and don't be afraid to use lots....I had my intake leak between the fuel rail and lower intake, and ford has a TSB and upgraded gasket to solve this particular issue as it's that common.

-andrew

 

[fordwheelinman]

Be sure and check the entire lengths of vacuum hoses, not just where they connect to the intake or a vacuum operated part. You may also have a busted/stuck egr valve that is allowing too much flow, and it could be possible that it isnt setting a code. Seen wierd things like that before.

 

[dirtyrice]

had the same problem and found vaccum leak using the cleaner method today. going to get elbow to fix tom. it was caused by radiator hose chaffing it through.

 

[Just_Randy]

I connected a voltmeter to the wires on my MAF as described here: http://www.therangerstation.com/tech_library/CleanMAF.html My voltage was bouncing between .3 and 1.3 very irratically. About that time I noticed the big hose clamp that clamps the airbox to the big hose was loose. So, I got a screwdriver and proceded to tighten that sucker down. As I did, the voltage steadied itself. The tighter I got the clamp, the more stable the reading.... and I was cranking on that clamp too! It continued to steady until I couldn't turn the screw anymore (indicating to me that even a fully tight clamp still leaks some). So, check for vacuum leaks EVERYWHERE. Anything from the piston to the aircleaner is fair game for a leak to cause MAF problems! Don't just check around the engine manifold.

As for me, I'm even thinking of using some type of sealer to glue all the plenum connections together.