Code P0171, what else do I need to check?

ROBERT CLARK2

MEMBER
2007 FORD FOCUS
2.0L
4 CYL
2WD
AUTOMATIC
200,000 MILES

I replaced the fuel filter and spark plugs; all were pretty bad. I plan on cleaning the MAF sensor. The code says lean in bank 1. It has 3 02 sensors. 1 on top, 1 2 inches away and 1 on the cat. I'm assuming bank 1 is the first one. I got a 02 sensor for upstream but it fits the second. So, I'm getting the one for the first one when I return it. Am I missing something I should check? I can't find any vacuum leaks. Also, it drives great but when I come to a stop light it kind of stutters for about ten seconds then it feels fine again. Then when I drive it's great until I have to slow down and stop.

1 Reply

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

A lean fuel mixture is usually a result of an engine vacuum leak. If you are sure there aren't any, by any chance do you have an exhaust leak before oxygen sensors? For example, is there a leak at the exhaust manifold?

I ask because an exhaust leak can indicate a lean fuel mixture. Also, it could be related to low fuel pressure. Have you checked the pressure to make sure it is within the manufacturer's fuel pressure specifications? If you haven't. I recommend doing it.

Here is a link that explains how to check pressure:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

You will need a fuel pressure gauge. However, most parts stores will lend one to you. I attached the manufacturer's fuel pressure specifications for you below.

Let me know. Also, I attached a pic below showing the possible causes related to the P0171.

Take care and let me know what you find.

Joe

See pics below.

Images (Click to make bigger)