DTC (Running Lean) Discussion

Lowtryx · 08-31-2009, 11:18 PM

At idle, operating temperature recieved P0174 (Running lean on Bank 2).

I'm thinking that this is due to one or a combination of the following factors:
Vaccum Leak
O2 Sensor
MAF Sensor

Tomorrow I'm going to check the voltage of both of my upstream O2's as well as Short and Long term fuel trim percentage. I'm fairly sure that if the reading is %15-%20 higher than it should be, chances are the vaccuum leak is the problem. I'm praying my cats are fine, High Flow Cats are anything but cheap, however I didn't recieve a Catalyst efficiency code and in any case both Downstreams were reading fine a few days ago when the light came on.

Just wondering if anyone has ever had any similar experiences with their stang. I'm very confident I will find and fix the problem in the next few days, just looking for reference.

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AirBrontosaurus · 08-31-2009, 11:58 PM

Your cats come after the O2 sensors, so they don't effect your fuel mixture. So, you can be relieved that your cats aren't causing this problem.

Logging the trims is a great idea, because that will tell you if it's an O2 sensor problem or a fueling problem. If your bank 2 STFTs and LTFTs indicate lean, but your bank 1 readings are OK, then you can be pretty sure that it's either a O2 sensor or an exhaust leak.

If it's both, then it's probably a fueling/MAF/vacuum problem. Your MAF may be dirty, or your fuel filter may be clogged or pump may be going bad, or you could have a vacuum leak.

The engine can do a pretty good job of regulating itself at idle/part throttle, so if you're getting a CEL it means the engine is way outside of its correctional abilities.

Post the STFT/LTFT values when you get them, that would be helpful. Hopefully you figure it out!

cliffyk · 09-01-2009, 10:11 AM

P0174 does not indicate a bad O2 sensor, but rather a good O2 sensor reporting a problem. The possible causes and diag tips (same as P0171) can be found here.

Since it's only reporting Bank 2 then I'd look for exhaust leaks upsteam (and less likely but possibe downstream) of the Bank 2 front sensor. Next check the fueling on that bank--injectors, blocked fuel crossover, etc.).

Things affecting both banks (MAF/intake, EGR, etc.) would be looked at after making sure the bank specific stuff as OK.

mustangman03 · 09-01-2009, 09:03 PM

Quote:

Originally Posted by cliffyk

P0174 does not indicate a bad O2 sensor, but rather a good O2 sensor reporting a problem. The possible causes and diag tips (same as P0171) can be found here.

Since it's only reporting Bank 2 then I'd look for exhaust leaks upsteam (and less likely but possibe downstream) of the Bank 2 front sensor. Next check the fueling on that bank--injectors, blocked fuel crossover, etc.).

Things affecting both banks (MAF/intake, EGR, etc.) would be looked at after making sure the bank specific stuff as OK.

Cliffy not say that ur wrong by no means but i have seen a car run lean on 1 bank but i was only 1 and it was bank 1 but like i said it was only 1 on a ford tarus just something to think about.

Lowtryx · 10-11-2009, 09:47 PM

As it turns out, the Intake Gaskets on both banks were leaking, causing a massive vaccum leak.

The way I diagnosed this, got an IDS Laptop and read the O2 PIDS while I sprayed Tune up cleaner around the intake. The resulting leaks allowed the cleaner to enter the engine, and thus was detected by the change in voltage from the O2's acknowledging and correcting for the mixture.

%100 certain of the leak.\

1999mustang2000 · 10-12-2009, 12:24 AM

i have this problem ive replaced the fuel filter the maf and still no help

fastbackford351 · 10-12-2009, 10:06 PM

Once again, MF'ers come through with good poop.
My car started tossing the same code a couple days ago.

aCiD · 10-12-2009, 10:32 PM

Quote:

Originally Posted by mustangman03

Cliffy not say that ur wrong by no means but i have seen a car run lean on 1 bank but i was only 1 and it was bank 1 but like i said it was only 1 on a ford tarus just something to think about.

I will. You're wrong. I just replaced a bad o2 sensor in my car that was falsely reporting too lean (throwing that code), and resulted in the car DUMPING max trim of fuel into bank 2, 33.3%.

1999mustang2000 · 10-12-2009, 10:36 PM

if ive replaced the fuel filter the maf and all eight coils...would you guys try the exhaust o2's next?

Bullitt2theHead · 10-12-2009, 10:59 PM

Before I ever replaced a MAF and coils, I would find the source of my lean code!!!

Honestly all it takes to find the source of a lean code is a can of brake cleaner and a basic obdII scantool that can see short term fuel trims. When your trim drastically change as you have sprayed something with brakeclean, you have found your leak and your lean code!