System Too Lean

Disturbed One · Oct 13, 2007

I'm still trying to figure out why I keep getting code: P0174, System Too Lean bank 2.

I have bassani mid length headers, O/r X pipe and cat back. I have the mil eliminators to shut off the rear sensors. It's hard to say but I've gone about a 3 weeks-month each time before the light comes on. The only time it seems to come on is when I'm driving in 5th gear. I originally thought it was cause I was running in 5th around 1500 rpm's but again today at 2g on the interstate it came on.

Does anyone have any idea why I keep getting this thrown? I can clear the code and be just fine for about a month before it does it again.

bhuff30 · Oct 13, 2007

Clean your MAF. Fords have an issue with the MAF getting dirty and causing a lean condition. It can even get so lean to throw a code.

The best way to clean it is using spray contact cleaner from radio shack. You want point it at the wire. Do no touch the wire, only spray contact cleaner on it. The problem being, that the wire gets coated with dirt/oil and airflow accross it does not register properly.

Do you have a K&N? Often, the oil will come off the filter and collect on the MAF. Even oil accumulated on the wire could throw a code, because it insulates the wire and prevents it from giving a proper flow reading.

steve_stang2003 · Oct 13, 2007

bhuff30 said:
Clean your MAF. Fords have an issue with the MAF getting dirty and causing a lean condition. It can even get so lean to throw a code.

The best way to clean it is using spray contact cleaner from radio shack. You want point it at the wire. Do no touch the wire, only spray contact cleaner on it. The problem being, that the wire gets coated with dirt/oil and airflow accross it does not register properly.

Do you have a K&N? Often, the oil will come off the filter and collect on the MAF. Even oil accumulated on the wire could throw a code, because it insulates the wire and prevents it from giving a proper flow reading.

+1

One other thing, if you use the Rat Shack cleaner make certain you DO NOT get the one with lubricant in it.
I'm not sure if they still sell that one but if you use it you will have a mess on your hands.

Scorcher2005 · Oct 13, 2007

Go to autozone and get the electronic cleaner. Make sure you get the lower strength one. It comes in a red and white can and has pictures of sensors on it. The heavy duty one has pictures of like an alternator or something and i was told that one may eat through the maf wires or something. The low strength one works excellent though.

Don 95Vert · Oct 14, 2007

If the MAF were the issue BOTH banks would show an error. The most probable cause is a tiny exhaust leak on the driver's side, somewhere ahead of the front 02 sensor. A tiny pinpoint leak will allow air leaks into the exhaust which will skew readings and trip the code. Other causes can be a vacuum leak on that side or an injector not firing for whatever reason. But 99% of the time it's an exhaust leak.
Don

bhuff30 · Oct 14, 2007

In fact, I have seem cases where a dirty MAF caused only one bank to run lean. My sisters 95 v6 stang did this last year. As it got dirtier, it threw a code on the other side too. Not to say that one side didn't have a pinhole leak on one side.

You are right, those are good things to check for, but cleaning the MAF is the most likely and easiest way to start troubleshooting it.

Don 95Vert said:
If the MAF were the issue BOTH banks would show an error. The most probable cause is a tiny exhaust leak on the driver's side, somewhere ahead of the front 02 sensor. A tiny pinpoint leak will allow air leaks into the exhaust which will skew readings and trip the code. Other causes can be a vacuum leak on that side or an injector not firing for whatever reason. But 99% of the time it's an exhaust leak.
Don

Disturbed One · Oct 14, 2007

Ty guys, I think that's a good place to start with cleaning the maf. I don't think it's an exhaust leak but very possible. I really appreciate the advice on what it could be. The vehicle did come with a mac CAI with the K&N and I cleaned the filter either really early this year or last year.

The only thing that was getting me though was it only did it in 5th gear and no other gears... so that's why I asked. I'll let ya know if I do have anymore problems in the future to see what is going on.

Robs96 · Oct 14, 2007

It is correct that a maf could cause one bank to read lean, but, 9 out of 10 times will read lean for both banks. I would look at the upstream o2 sensor. These are usually the culprit. Read the v6 tech column. I had similar condition except code 171 lean for pass bank. O2 all the way in my case. An air leak, rotten hose, improperly sealed something or other, bad pcv.....there are multiple causes and to be honest if the maf fixes this I will be surprised. Worth a try for a quick cheap fix if it works.

System Too Lean

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