I could use some help solving these pesky lean codes. I've hade this rager for 6 years and I have received this codes alot. These recent codes could not be fix with the usual methods I usually use to fix them. So far I have change the spark plug, air filter, fuel filter, MAF sensor, and the O2 sensor.
I borrowed a scan tool to get some values to see if it might give me a clue. I read somewhere if you rev your engine and your fuel trims fall to 0 or negative you may have a vacuum leak. I tried this and two of my fuel trim values fell below 0 but which ones I cant remember.

I check for vacuum leaks with the soapy water and carburetor cleaner, but their are alot of hoses and some are taped up. I didn't see any indication of a vacuum leak but I think I can hear one, its hard to tell over the engine noise.

I also pull the hose of the pcv valve while the engine was running to see if it had any pressure, it does and it immediately shut down the engine when I pull it.

Any help will greatly appreciated,

have you changed all 3 O2 sensors

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There only two on that truck I thought

look on the back of your engine for the pcv (i think) valve. its a rubber tube that is molded at a 90 degree angle. Mine had a rip in it and it caused my truck to have those codes 6 months ago

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1988 Ranger XLT 2.3L 5spd 2wd. SOLD
2003 Ranger XLT 3.0L Auto 2wd. Custom Interior. SOLD
1975 F250 Highboy 390 4spd Factory on 35's. SOLD
1992 F150 4x4 5.8L Std. Cab Long Box. SOLD
1995 S.A.S. Ranger Ext Cab. 4.0L 5spd. 5.13 gears front and rear. Lockright Lockers front and rear. Disks all the way around. (New toy )

I know that hose your are talking about, I pull it off and check it. Its not the cause of my problem.

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Humm so there is a third O2 sensor. Do you think thats why my scanner is showing n/a value for the short term fuel trim and do you think that would cause a code Po174/171

my best guess is a vacume leak somewhere

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1988 Ranger XLT 2.3L 5spd 2wd. SOLD
2003 Ranger XLT 3.0L Auto 2wd. Custom Interior. SOLD
1975 F250 Highboy 390 4spd Factory on 35's. SOLD
1992 F150 4x4 5.8L Std. Cab Long Box. SOLD
1995 S.A.S. Ranger Ext Cab. 4.0L 5spd. 5.13 gears front and rear. Lockright Lockers front and rear. Disks all the way around. (New toy )

Looking at your fuel trim values, it shows they are enriching the map 20-25%. Since you are cruising at 53mph when this happened with only 28% load I would say it is most likely a vacuum leak. Try stealing some freeze frame logs or just manually recording your fuel trims under high load - my guess is they will come closer down to zero, validating my assumption that it is a vacuum leak.

If the mods would have sticky'd this, you could have just searched for the answer.

Click here:

http://www.fordrangerforum.com/elect...171-p0174.html

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Looking for a professional retrofitter to add HIDs or LEDs to your Ranger? PM me if your looking to have work done, and have cash to spend.

Thanks I search and read your post on po171/174 early. It was very informative, but I was confused because you said that negative PID value indicates that fuel is being reduced to compensate for a rich condition but I notice my trim values go negative and I have a lean conditions. I'm not sure if these were long term or short term values but I will borrow that tool again and get same freeze frame values. Does the scanner get the freeze frame values from what is stored in the PCM or are these values taken at the same time you scan them with the tool. I thought I was at idle when I ran the tool, not 53mph.

The freeze frame is a picture of what was going on when the vehicle threw the code. With lean/rich codes it has to be above 10% or so correction for a certain period of time.

If the map was going negative, that would mean it is pulling fuel. It is positive because it is trying to dump fuel to make it less lean, or closer to stoic.

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Looking for a professional retrofitter to add HIDs or LEDs to your Ranger? PM me if your looking to have work done, and have cash to spend.

I have the same error codes PLUS P0402. 2001 4.0 125 K. .

Update
Ordered a new O2 sensor today to replace that third sensor. Will install it this weekend.

you just wasted your money!

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Looking for a professional retrofitter to add HIDs or LEDs to your Ranger? PM me if your looking to have work done, and have cash to spend.

I thought I would go ahead and change the O2 sensor since one of them was showing n/a on my sensor data. Looks like I'm going to just have to take it somewhere because this vacuum leak is very hard to find.