Contour Enthusiasts Group Archives Forums General Troubleshooting OBD-II code P0171 or P0174

I'm new here, I got a '97 contour "sport" 4cyl. the check engine light came on, my girlfriend's brother took it to autozone where he works and said the code was for left bank running lean and that he doesn't know what that means. The OBD-II codes on your web site seem to point to either P0171 or P0174. Now my question what could this be? The car has 74k miles on it, the throttle lags when pushed from idle and the engine knocks above 4500 rpm. Just tuned it up( new plugs, wires, airfilter, oil change). The throttle lag is the most annoying problem especially when I've just started the engine and I go to push the accelerator and it lags so much it almost stalls. I can tame the knocking with high octane gas, but I thought it should handle normal gas with out knocking.
I'd really appreciate any help in this matter thanx

Is it the only CEL that you received? Sometimes there is more than one CEL recorded.

The following is from the Ford TSP:

Diagnostic Trouble Codes (DTCs) P0171 bank (1) (cylinder #1) and DTC P0174 bank (2) indicate the fuel/air ratio is too lean. The fuel adaptive 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 adaptive syste 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.
-- Contaminated injector(s)

Induction system
-- Air leaks after the MAF.
-- Vacuum leaks.
-- Restricted air inlet.
-- PCV system.
-- Fuel purge system.
-- Improperly seated dip stick.

EGR
-- 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 air intake for leaks, obstructions and damage.
* Check air filter, air filter housing for blockage.
* Verify integrity of the PCV system.
* Check for vacuum leaks.

Welcome! For future reference, it's always best to have the actual code that was read when you have a Check Engine Light (CEL), because we can get right to the point.

From the info you've given, I'd say the first, most likely culprit is the Oxygen Sensor closest to the engine.

Forget the "bank" nomenclature, as your inline 4 cylinder has only one bank. Us V6 guys are the only ones lucky enough to have to deal with that confusion.

You have 2 oxygen sensors. One, closest to the engine, is for control of the air/fuel ratio. This one is important and can lead to the driveability problems you're reporting if it goes bad.

The second one, after the catalytic converter, is an emissions sensor to monitor the cat and alert the driver to one that is going bad. If that sensor goes, you would never notice except for a CEL staring you in the face.

However, without the code I can't say for sure. There could be other things that would cause that problem. Take a ride to any Autozone (or your g/f's brother's store) and get the actual code number. Myself or someone else can copy and paste the exact instructions from the Ford Service Manual. Don't go throwing parts at the problem - that can get very expensive very quickly. We'll take care of you.

Or, you can beat me to it.