Running lean, codes P0174 and P0171

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?

6 Replies

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

JAEDAV12

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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

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

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

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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