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Dan
Dan, Technician
Category: Ford
Satisfied Customers: 23587
Experience:  Independent Shop Experience, 2 Year Automotive Diploma, & Access to Information Database
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I have a 2004 f150 it keeps giving me codes p0171 and p0174

Customer Question

i have a 2004 f150 it keeps giving me codes p0171 and p0174 i replace the catalitics all 4 O2 sensors and the MAF sensor MAF was the last thing i did before i replace it the CHECK ENGINE light wll take 2 or 3 days to come back on with the same codes after i replace the MAF i erase the codes and now the CHECK ENGINE light comes back on after just 5 minutes of been clear
Submitted: 1 year ago.
Category: Ford
Expert:  Roger replied 1 year ago.

Hello, I'd be happy to help! First, what engine does your truck have?

Customer: replied 1 year ago.
4.2
Expert:  Roger replied 1 year ago.

Ok do you have access to a scan tool that shows live data?

Customer: replied 1 year ago.
no just a globall OBD code scaner
Expert:  Roger replied 1 year ago.

It's very likely you have an intake manifold gasket leak, they are extremely common on the 4.2L engines because of poor design of the isolator bolts.

Expert:  Roger replied 1 year ago.

The other possibility is a vacuum leak, which I assumed you've checked for already. If not do that. If there is no leak I would go with the intake manifold set and the isolator bolts for the manifold, dealer parts only. Because all you have is a code reader there's no way to diagnose it correctly because we need to see fuel trims to diagnose that, but like I said they're extremely common I've done my fair share if them. If you have any more questions let me know. Please don't forget to rate, they won't compensate me unless I've been rated. Thank you!

Customer: replied 1 year ago.
i replace the intake gaskets 30 days a go after that it just give me a code for the throtle position sensor i replace and then i got the 2 codes p0171 and p0174 the exaust had a bad leat at the conection of the down pipe and exaust manifold so i replace the whole catalitics assembly with O2 sensors and the MAF
Customer: replied 1 year ago.
BUT I WLL RE CHECK THE GASKETS OR REPLACETHEM AND IWLL GET BACK WITH YOU THIS AFTERNUN
Expert:  Roger replied 1 year ago.

Did you replace those bolts as well with the updated bolts? Did you do upper middle and lower or just upper, and did you tighten them I'm the correct order?

Expert:  Roger replied 1 year ago.

Hello, just wanted to check on your truck and see if you've had time to figure out anything. If you have any more questions let me know, and keep me updated on your progress. Please don't forget to rate, they won't compensate me unless I've been rated. Thank you!

Expert:  Dan replied 1 year ago.

I'd also like to mention the PCV hose is common to leak and PCV can stick open causing this code. So assuming gaskets are not leaking i'd start by giving PCV hose a good look and replace PCV with one from dealership. Let me know how it goes or if you run into questions, thanks.