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Old 06-24-2019, 07:56 AM   #1
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Code P0171 System too Lean. (not the PCV hose)

My 2007 Duratec 2.0L, 5 speed is throwing code P0171. I put a new PCV hose on thinking that was the problem but their was nothing wrong with the old hose. I cleaned the MAF sensor.

Light is still on.

I don't hear any obvious vacuum leaks. I sprayed starting fluid around and used propane to check for leaks. Nothing I can see. Car starts and idles fine.

What else to check?

P.S. I was able to change the PCV hose fairly easy without removing the intake manifold. Simply remove the two 13mm bolts holding the starter. Slide it over to access the bottom of the hose. Use 11" pliers to undo the clamp and a long bar to pry it off. (see picture of "special" tools) Top of the hose clamp can be accessed between number 3 and 4 intake ports. The hardest part was prying the hose off and on the intake port. Make a small cut to get the hose off. Use motor oil as a lubricant to pry the new hose on. Pretty easy job. Took me about 1.5 hours. I can't believe everyone removes the intake. Unfortunately in my case there was nothing wrong with the hose.


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Old 06-24-2019, 08:16 AM   #2
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How does your o2 sensor 1 read? And what's your fuel pressure at idle?

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Old 06-24-2019, 08:18 AM   #3
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If that's at idle your MAF is reading unusually high...

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Old 06-24-2019, 08:29 AM   #4
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Originally Posted by calpdavis View Post
How does your o2 sensor 1 read? And what's your fuel pressure at idle?

Cal

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I'm not sure how to check o2 sensor.

I'll have to put the car on a different scanner to check the fuel pressure? I don't think that is in the freeze frame data on my reader?

Or can I see fuel pressure in the diagnostic mode on the dash?
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Old 06-24-2019, 08:30 AM   #5
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Originally Posted by calpdavis View Post
If that's at idle your MAF is reading unusually high...

Cal

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The freeze frame data shows 883 rpm and 5 km/hr. I cleaned the MAF sensor.
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Old 06-24-2019, 08:32 AM   #6
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Fuel pressure would need to be read with a manual gauge.

Your bank 1 o2 sensor 1 should rapidly switch between .1-.9ish volts

What's MAF read at idle?

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Old 06-24-2019, 09:07 AM   #7
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Quote:
Originally Posted by calpdavis View Post
Fuel pressure would need to be read with a manual gauge.

Your bank 1 o2 sensor 1 should rapidly switch between .1-.9ish volts

What's MAF read at idle?

Cal

Sent from my moto g(6) using FF Mobile
How do I check those? I don't know too much about this stuff. I know how to plug my scanner in and read the code. That's about it, lol. I have the freeze frame data but I don't understand it.
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Old 06-24-2019, 09:22 AM   #8
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1. You're gonna need a fuel pressure gauge kit to read fuel pressure

2. You're gonna need a scan tool that can read live data.

If you don't have one, or a friend with access to one, our suggestions are as good as throwing a dart at a list of related parts. Could be low fuel pressure which would be fuel pump, or fuel filter, or fuel pressure regulator. Could be restricted injectors. Could be a bad MAF sensor. Could be a bad 02 sensor. Could be a vacuum leak you're not hearing.

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Old 06-25-2019, 09:26 PM   #9
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The fuel pressure, according to the freeze frame data was approx 39psi.....though needs to be checked using an actual fuel pressure tester.

Unless the code was set seconds into cold starting the vehicle, the upstream O2 sensor (O2S B1 S1 in the pic) should be above 0.050V..... Judging by the 69C ECT reading, I suspect that wasn't the case.

How many miles are on this Focus??
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Old 06-26-2019, 07:50 AM   #10
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Quote:
Originally Posted by sykozis View Post
The fuel pressure, according to the freeze frame data was approx 39psi.....though needs to be checked using an actual fuel pressure tester.

Unless the code was set seconds into cold starting the vehicle, the upstream O2 sensor (O2S B1 S1 in the pic) should be above 0.050V..... Judging by the 69C ECT reading, I suspect that wasn't the case.

How many miles are on this Focus??
Hi, thanks for your reply.

the car is a 2007 with about 135,000 miles on it.

I believe the engine light came on after I had been driving it for a while. I can't say for sure though. I've reset it a couple times.

So you suspect a faulty oxygen sensor? How would I know which one? I see 3 of them right off the back of the engine.

I can't find any obvious vacuum leaks. PCV hose is fine. Fuel filter has been changed. I need a new muffler but I don't think that would cause it. The car starts, idles and drives smooth.
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