codes 172,174; banks 1 & 2 running lean

[rowdy51]

my 1998 F-150, with 4.2 V6 has these codes from time to time; they always seem to come on when slowing to stop; have researched these codes and know what all will turn the check engine lite on; but I can't seem to find out what it actually is; I live in one of the counties where my vehicle has to pass emissions test in order to buy tags for it; plus, I just want my venicle running right; any and all help is appreciated; are there any common problems with this condition;

 

[blacksnapon]

my 1998 F-150, with 4.2 V6 has these codes from time to time; they always seem to come on when slowing to stop; have researched these codes and know what all will turn the check engine lite on; but I can't seem to find out what it actually is; I live in one of the counties where my vehicle has to pass emissions test in order to buy tags for it; plus, I just want my venicle running right; any and all help is appreciated; are there any common problems with this condition;

P0172, P0171, P0174 AND P0175: FUEL SYSTEM AT THE CORRECTED FUEL TRIM
Diagnostic Trouble Codes (DTCs) P0171 bank 1 (Cylinder 1) and DTC P0174 bank 2 indicate the fuel/air ratio is too lean. The fuel trim system is at the rich correction limit.

DTC P0172 bank 1 and DTC P0175 bank 2 indicate the fuel/air ratio is too rich. The fuel trim system is at the lean correction limit.

DTCs HO2S Reference list:

HO2S-11 = DTCs P0171 and P0172
HO2S-21 = DTCs P0174 and P0175
Possible causes:

Fuel system

Excessive fuel pressure.
Leaking fuel injector(s).
Leaking fuel pressure regulator.
Low fuel pressure or running out of fuel.
Contaminated fuel injector(s).
Vapor management valve (VMV) leaking.
Induction system

Air leaks after the MAF.
Vacuum leaks (vacuum lines and gaskets).
Restricted air inlet.
PCV system.
Fuel purge system.
Improperly seated engine oil dipstick.
EGR System

leaking gasket.
Stuck open EGR valve.
Leaking diaphragm.
Base engine

Oil overfill.
Cam timing.
Cylinder compression.
Exhaust leaks before or near the HO2S(s).
Check intake air system for leaks, obstructions and damage.
Check air cleaner element, air cleaner housing for blockage.
Verify integrity of the PCV system.
Check for vacuum leaks.

 

[jbish28]

There are a lot of contributing factors to your issue. Without knowing what kind of scan tool you are using it is hard to say. If I encountered this problem with a customer vehicle I would be looking at o2 sensors, maf sensor, fuel trim and bare data to see why the ecu is correcting to lean. Those codes are telling you that know how much fuel the ecu commands, it cannot get it rich enough. Check for vacuum leaks by spraying some carb cleaner around the intake and all the vacuum lines. Also spray it near your pcv hoses. Check for a fuel restriction with a fuel pressure gauge WHILE driving. Check your connections at the mass airflow sensor and also your fresh air ducting to make sure it is installed properly. Perhapstake the maf sensor off and inspect the wires to be sure there is no debris. after all that if you still have a problem write back.

 

[rowdy51]

using the SunPro scan tool; my mistake on earlier post; codes are 171, 174; changed the elbow under t-body; but didn't help; ( a friend at work had same thing on his 99, it fixed his problem took it easy on my driving for a few days, shifting to neutral every time I stopped; finally got enough drive time on comp to pass emissions testing and got new tags; seems like the codes come in when I am slowing down for a complete stop; this had happened 2 times before and I changed O2 sensore both times and it lasted about 12-14 months before happening again; I tee-ed off the vac line going to the VMV, it was reading about 17" vac; can clamp off this same vac line and vac goes up to about 19 1/2" vac; what kind of vac should I see on engine setting running idle; engine is not running rough at idle; I do appreciate all your help;

 

[rowdy51]

the vac lines and system are very difficult to get to, plus I have to work outside, so it had been very slow working on it, depends on weather;

 

[blacksnapon]

From this point, its going to involve detective work on your part. Pay attention to my earlier post, and jbish's post. In there is your answer. Lean conditions are never easy. Best of luck.