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Discussion Starter #1
If someone can help me solving a lean condition issue, I'd appreciated!

I bought a 2002 Ford Focus ZTW (Zetec, at 100k miles) a month ago, and I noticed OBD2 always reads LTFT for both bank 1 and 2 reading pretty high at 10-25%. 10-15% at idle, and goes up at higher RPMs. I haven't seen any trouble codes yet, but gas mileage hasn't been very good. I've ruled out vacuum leak since LTFTs don't improve at high RPMs. The both banks read similar values, so I've concluded the cause is either a dirty/faulty MAF sensor or fuel delivery issue.

I cleaned the MAF sensor with the CRC MAF sensor spray a few days ago with no noticeable improvement.

Today I unplugged the MAF sensor, disconnected the negative battery pole for 10 minutes and started the car. While on idle, OBD2 continuously read STFT (short term fuel trim) high at 10 to 30%, again with similar numbers for both banks. After 5 minutes of idling, the engine stopped by itself.

I'm cleaning the MAF sensor for the second time, this time more thoroughly with isopropyl alchol as well as spray, just in case.

On the fuel-delivery side, the fuel pump was just replaced a month ago (thus ruling out), and the fuel pressure reading on OBD2 is pretty steady around 40psi. I read that a clogged fuel filter affects fuel volume but not always pressure, and with my car having reached 100K miles, I might as well change the filter now.

I've also noticed a small crack on the PCV hose (longer piece), and since this seems a common issue for the model, replacing the PCV valve and hose is next on the list.

Am I on the right track on diagnosing? Anything else I should look into? I would certainly appreciate sharing your knowledge and experience!
 

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Bank 2 numbers means nothing as you have no bank 2. Bank 2 is the other bank of the engine on a V-6 or V-8.

Fix the PCV hose, the most common vacuum leak on those engines.
 

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Discussion Starter #3 (Edited)
Bank 2 numbers means nothing as you have no bank 2. Bank 2 is the other bank of the engine on a V-6 or V-8.

Fix the PCV hose, the most common vacuum leak on those engines.
Thank you for your reply! Ah, please excuse my ignorance. I see a Dorman hose (part# 46030) for only $16 on Amazon with good reviews, so it's well worth a shot, plus the valve replacement is part of required maintenance anyway.

What I've learned is that vacuum leak makes LTFT go down as RPM increases...? My LTFT goes up as I rev up. In any case, I'll update after replacing PCV hose/valve!
 

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I've ruled out vacuum leak since LTFTs don't improve at high RPMs.

While on idle, OBD2 continuously read STFT (short term fuel trim) high at 10 to 30%, again with similar numbers for both banks. After 5 minutes of idling, the engine stopped by itself.
FTs below +/- 10 are normal. LTFTs are just that - long term, over many drive cycles - and should not change much just reving the engine. In your case with positive FTs the engine is lean so fuel is being added. I would NOT rule out anything - especially a vacuum leak, either at the PCV hose or anywhere else. I also would not rule out bad (old) O2 sensors. Are your O2s switching normally and have you ever replaced them?

Inline engines only have one bank. Are you sure you have a bank 1 and bank 2 sensor and not a bank 1 sensor 1 and bank 1 sensor 2 (sometimes abbreviated HO2S11, HO2S12 on data PIDs)?

Paul
 

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Discussion Starter #9
FTs below +/- 10 are normal. LTFTs are just that - long term, over many drive cycles - and should not change much just reving the engine. In your case with positive FTs the engine is lean so fuel is being added. I would NOT rule out anything - especially a vacuum leak, either at the PCV hose or anywhere else. I also would not rule out bad (old) O2 sensors. Are your O2s switching normally and have you ever replaced them?

Inline engines only have one bank. Are you sure you have a bank 1 and bank 2 sensor and not a bank 1 sensor 1 and bank 1 sensor 2 (sometimes abbreviated HO2S11, HO2S12 on data PIDs)?

Paul
Thanks for your input! Right, I did read that for some people LTFTs didn't change until they drove 100s of miles. For the O2 sensors I get readings from bank1 sensor 1 and bank 1 sensor 2 and no data for any sensors from bank 2. I think they were switching correctly between 0.1 to 0.9v, at least for sensor 1 from what I remember, but I'll double-check and try recording a video of live graphs for both sensors - I'll post it here.
 

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Discussion Starter #10
You should take the Batt loose about 5 min and back on and be watching the stft not the ltft

The stft is as its happening

Tom
Thanks for your tip! When I took the battery pole off and started afterwards, LTFT was flat at 0% for about 10 minutes and STFT generally kept increasing to as high as 35%, never going into negative.

As I learned in YouTube videos, maybe I could do a carb cleaner test for hunting vacuum leaks - if I hit a leak, that should affect STFT and O2 sensor reading, right?
 

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No mods... except I did notice that the PCV hose seems to have been cut shorter and connected to another hose piece with some metal piece in between held tight with two clamps. Strange...
Please keep in mind that the factory system from the intake manifold to the PCV valve uses two sections of hose with a rigid tube section in between (although it sounds like your setup may be non-factory).

Paul
 

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Discussion Starter #17
Please keep in mind that the factory system from the intake manifold to the PCV valve uses two sections of hose with a rigid tube section in between (although it sounds like your setup may be non-factory).

Paul
That's right, there is that metal tube that goes by the side of the engine... The fix I mentioned was found at the back of the engine where the tube goes back to the intake manifold. I learned that's where the pipe is most likely to collapse. I'll get the replacement hose in a few days so I'll post a photo of the old hose... and will report if the problem is fixed. Thank you for all your input!
 

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Not a problem pal, I had just forgotten about the steel tube bolted to end of head. Sounds like somebody has messed with the other end of the piece in back though.
 

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Your data isnt very informative because it only shows the peeks and not the low side and you need to see both , your off by 2% just on the peeks which isnt much to worry about but what about the low side

The your LTFT is on and we cant see how much it has already corrected for your stft

Tom
 
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