Recommendations
Fleet Owner
Joined: Apr 2008
Posts: 24,322
Likes: 5,132
From: 0,0,1
Vacuum leak misfires are old school predating engine computers as we know them today. In today's world with a vacuum leak the computer can compensate to a point by enriching the mixture. OTOH misfires allow excess fuel into the exhaust, in turn the O2 sensors see less oxygen and figure the system is running rich, so the computer leans out the mixture, hence the P0174 code.
Logistics Pro
Joined: Jan 2001
Posts: 3,740
Likes: 37
From: Central NYS
You want to check the freeze frame data to see if the engine was under load when the code set. If it was , check the fuel filter and the fuel pump pressure. Inadequate fuel supply can cause a lean misfire and/or the lean code. Additionally the freeze frame will show the fuel trims so you can see if the PCM was trying to compensate, and if it was compensating on one or both banks.
If the engine was unloaded look for a vacuum leak.
Fleet Owner
Joined: Apr 2008
Posts: 24,322
Likes: 5,132
From: 0,0,1
Might want to double check that bud.
Logistics Pro
Joined: Jan 2001
Posts: 3,740
Likes: 37
From: Central NYS
alloro, I tried the PM thing but it said you are not accepting PMs.
See page 9 of this document. It explains better than I can what happens to O2 content of exhaust gasses when a misfire occurs.
http://www.autoshop101.com/forms/h56.pdf
See page 9 of this document. It explains better than I can what happens to O2 content of exhaust gasses when a misfire occurs.
http://www.autoshop101.com/forms/h56.pdf
Postmaster
Joined: Sep 2010
Posts: 3,472
Likes: 2
From: Southern Cal
alloro, I tried the PM thing but it said you are not accepting PMs.
See page 9 of this document. It explains better than I can what happens to O2 content of exhaust gasses when a misfire occurs.
http://www.autoshop101.com/forms/h56.pdf
See page 9 of this document. It explains better than I can what happens to O2 content of exhaust gasses when a misfire occurs.
http://www.autoshop101.com/forms/h56.pdf
New User
Joined: Sep 2011
Posts: 7
Likes: 0
Not too familiar with this thread but have worked on an 03 Expy and now have an 04. I have codes P0171 and P0174 currently on my 04. It had jumped to some other ones combined with the P0300 but got those to go away.
So, after reading numerous things online I am still trying to resolve the codes. I have replaced all 8 spark plugs with the OE motorcraft plugs, and I replaced the Heated PCV valve and line(infamous rear intake elbow) and still have the 171 and 174 codes.
Had it looked at by a mechanic who had checked for vacuum leaks...
Checked the MAF sensor and had cleaned it before the codes came on...
Any ideas what it could be? I am deployed so can't try any fixes right now but trying to think of things it could be so can tell my wife to tell the mechanic if it comes to that. Or, I will try when I return...Thanks for any input.
So, after reading numerous things online I am still trying to resolve the codes. I have replaced all 8 spark plugs with the OE motorcraft plugs, and I replaced the Heated PCV valve and line(infamous rear intake elbow) and still have the 171 and 174 codes.
Had it looked at by a mechanic who had checked for vacuum leaks...
Checked the MAF sensor and had cleaned it before the codes came on...
Any ideas what it could be? I am deployed so can't try any fixes right now but trying to think of things it could be so can tell my wife to tell the mechanic if it comes to that. Or, I will try when I return...Thanks for any input.
New User
Joined: Sep 2011
Posts: 7
Likes: 0
Thanks for the input sarge...I thought about that being a possibility, but ugh...PIA to replace that...(did it on my 03 but ended up being a secondary fuel pump relay-another story)
I forgot to mention that I did replace the fuel filter and the air cleaner was also cleaned(not that that would cause a lean condition)
Haven't hooked up a fuel pressure tester but will keep the fuel pump idea in mind....and hey! I still have the one from the 03!! since it didn't end up being faulty...that will save $300...
What O-rings would be replaced? I saw that on some other comments somewhere...Thanks again!!
I forgot to mention that I did replace the fuel filter and the air cleaner was also cleaned(not that that would cause a lean condition)
Haven't hooked up a fuel pressure tester but will keep the fuel pump idea in mind....and hey! I still have the one from the 03!! since it didn't end up being faulty...that will save $300...
What O-rings would be replaced? I saw that on some other comments somewhere...Thanks again!!
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
3 Best / 3 Worst Parts of Modern Ford Ownership
Brett Foote
10 Amazing Upgrades That Solve Common Ford Truck Owner Headaches
Pouria Savadkouei
Every 2026 Ford Engine Explained
Brett Foote
10 Ugly Ford Trucks That We Still Kinda Love
Joe Kucinski
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
Thread
Thread Starter
Forum
Replies
Last Post
sniknah
1997 - 2003 F150
7
May 18, 2011 06:23 PM
ToolTime
1997 - 2006 Expedition & Navigator
3
Jan 5, 2007 09:27 PM
Skywalker1980
1997 - 2006 Expedition & Navigator
2
Jan 23, 2004 04:08 PM