Running lean, codes P0174 and P0171

Tiny
JAEDAV12
  • MEMBER
  • 1998 FORD EXPEDITION
  • 5.4L
  • V8
  • 2WD
  • AUTOMATIC
  • 76,664 MILES
So yesterday I changed my fuel injectors, ignition coils, and spark plugs due to a misfire I was having. I previously replaced the fuel pump along with the mass air flow sensor and PCV valve. But after changing the injector spark plugs and coils code P0174 and P0171 popped up. There was a previous O2 sensor code present before changing everything. So was there something I possibly did wrong to cause the truck to run lean all of a sudden?
Wednesday, May 6th, 2020 AT 4:47 PM

6 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good evening,

Did you check for any vacuum leaks?

https://www.2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers

Do you have a scan tool that can read long term trims?

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

I know you replaced the fuel pump but can you give me the pressure?

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

Did you do a compression test as well?

https://www.2carpros.com/articles/how-to-test-engine-compression

Roy
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Wednesday, May 6th, 2020 AT 5:06 PM
Tiny
JAEDAV12
  • MEMBER
  • 46 POSTS
Yes, I did check for vacuum leaks couldn’t find anything. Will have to do a further investigation once engine cools. Fuel trims for long term were 24% short term 5-7%. Haven’t check fuel pressure yet as well as a compression test. But as stated in the previous message this didn’t happen until I changed the fuel injectors, coils and plugs.
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Wednesday, May 6th, 2020 AT 5:15 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Okay, 24% is high which means there is a severe lack of fuel being injected into the motor.

What brand fuel pump? What brand injectors?

What about the mass air flow? Make sure the hose from it to the throttle body is not leaking or cracked. That will allow un metered air into the system and will cause these codes.

Roy
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Wednesday, May 6th, 2020 AT 5:18 PM
Tiny
JAEDAV12
  • MEMBER
  • 46 POSTS
Fuel pump is a Bosch so are the injectors and the mass air flow sensor is Motorcraft OEM and are you talking about that green and red hose coming from the top back of the throttle body?
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Wednesday, May 6th, 2020 AT 5:22 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Yes, look for any cracks in the hose.

Also, check the PCV. You were working around there as well. Make sure that hose is intact.

The PCV is in the right front valve cover.

This issue sounds like it may be something you did not connect or a possible cracked hose. Go over your work just to be sure.

Roy
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Wednesday, May 6th, 2020 AT 5:38 PM
Tiny
BMDOUBLE
  • MECHANIC
  • 1,139 POSTS
The easiest way to verify a concern with a vacuum leak is to monitor o2s11 and o2s21 sensor voltages while spraying certain parts of the intake. When the volts spike up, bingo! You've found it. Just something that has worked for me.
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Wednesday, May 6th, 2020 AT 6:13 PM

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