lean fuel trim
Thread Starter
Intermediate
Joined: Aug 2013
Posts: 25
Likes: 0
lean fuel trim
in my 2002 I got P0171 and P0174 codes on both banks. Both LTFTs are at 25%. I checked fuel pressure it's at 65. I sprayed with carb cleaner all vacuum connections under the hood. Nothing. Please advise
Safety Car
Joined: Jul 2005
Posts: 3,572
Likes: 9
From: Jackson Tn
St. Jude Donor '06-'07-'08-'09
sounds like it's getting lean if the LTFT are adding that much fuel. may be lack of fuel pressure. or clogged filter? is it maintaining that pressure?
are you sure you don't have a vacuum leak anywhere?
are you sure you don't have a vacuum leak anywhere?
Last edited by printmanjackson; Aug 4, 2013 at 04:46 PM.
Thread Starter
Intermediate
Joined: Aug 2013
Posts: 25
Likes: 0
fuel pressure is at 65 so I don't think I have fuel pump or filter issue. I sprayed vacuum lines under the hood. I guess leak in the HVAC control system (flaps controlling air distribution within instrument panel) may be a problem but it would be hard to check. I found a neat idea on line to use a stage smoker (for shows) as vacuum line smoker. So I want to buy one and convert it to an "automotive tool"
Instructor
Joined: Oct 2009
Posts: 215
Likes: 1
From: Roseville CA
Check the vacuum at the manifold with a gauge. Also check that you dont have an exhaust leak making the car think it is running lean. Also, you can always go old school and look at the plugs. If they look lean, they are 
But if they look rich, you probably have an exhaust leak that is tricking the o2's into thinking you are lean. My 2 cents...
But if they look rich, you probably have an exhaust leak that is tricking the o2's into thinking you are lean. My 2 cents...
Race Director
Joined: Jan 2008
Posts: 16,028
Likes: 170
From: oregon
absolutely
as others have said do you have any pcv or exhaust leaks?
also do you have black carbon all over the exhaust tips?
may pull and easy spark plug to look at as well
if it's really rich there's either oxygen getting at the o2 via a leak or a bad o2
as others have said do you have any pcv or exhaust leaks?
also do you have black carbon all over the exhaust tips?
may pull and easy spark plug to look at as well
if it's really rich there's either oxygen getting at the o2 via a leak or a bad o2
Instructor
Joined: Dec 2012
Posts: 191
Likes: 23
From: Louisville KY
I know this sounds too simple, but I fought the same thing for weeks. My issue was self inflicted. The K&N air filter was over oiled and oil got onto the MAF sensor. If you have an oiled AF, try cleaning it and running dry for a while to confirm the problem, you will also need to clean the MAF sensor with the proper MAF sensor cleaner. Give it a try, what do you have to lose?
