Contour Enthusiasts Group Archives Forums General Troubleshooting Same O2 sensor codes after sensor replacement-OBD1

The end of last winter and early fall when temps were colder I was getting a CEL intermintenly when I believe system went into closed loop.

I get the following Memory codes:
� 172 & 176: Front and Rear O2 sensors not switching, system is or was lean.

Before I replaced both O2 sensors I checked the best I could for any vacuum leaks. Sprayed cleaner around U/L intake gaskets and PCV hose to see if I could notice a RPM change. No difference. So I decided to replace the OE sensors (3 wks ago) hoping to eliminate the constant memory codes I have been getting. Even hooked my scanner while driving after swapping out sensors to read data stream. The CEL light came back on while driving( 4 days later when temps started dropping) and then goes off again w/ the same memory codes. I get a slight uneven idle at stops and while at highway speed I can feel a very slight buck/jerk. Once the engine reaches normal operating temperture, the light goes off and I will not experience any drivability problems. I only experience the CEL and a minor drivability problem after the car has been sitting overnight or a long time when the temps go below 40 degrees. It seem if I warm up the engine for 10-15 minutes before driving, everything is normal. But if it is cold and I start right out I can "feel" the CEL about to come on before it actually does.

If there is a slight vacuum leak, why are the problems only happening during cold weather? I am sure others have had the same scenario w/ their Duratecs. I have yet tried to clean the MAF w/ electric contact cleaner. I have read where this may cause problem if it is dirty. I can also hook up my fuel guage to measure the psi, but I feel if it was a fuel delivery issue, I would be experiencing this problem all the time.

Now with constant colder temps, I do not feel like getting into anything deep in a cold garage. I just want to know what the culprit is that is making my brand new Bosch O2 sensors seeing this lean condition.

Any insight to this air/fuel problem would be greatly appreciated!

Cold weather needs more fuel because it doesn't evaporate as quickly is the engine needs. Carbs had chokes to shut off some of the air so the system adds more fuel. Fuel injection just runs a program that will open the injectors longer. But on any system if there is a vacuum leak that air is unmetered so it doesn't know to add additional fuel. Your old O2 sensors were probably still working. When the mixture got real lean they stopped sending voltage or the voltage was real low.

Unplug the MAF. If the drivability issues go away, you know it's at fault. The computer system will use default values in its place. You will have a CEL.

Steve

I would have to agree there is unmetered air entering the intake when the metal to gasket surface is cold. When the metal absorbs heat is will "seal" the vacuum leak and return to the correct air/fuel mixture.

A likly culprit may be a leak in the fuel rail to intake manifold seals. They become hard with time and fail to seal the fuel rail to the lower intake manifold, causing unmetered air to enter the head. My O2 sensors are seeing this lean condtion and causing an erratic idle and slight buck at highway speeds. When the correct operating temp is reached the vacuum leak is eliminated. Hence, the air/fuel mixture is perfect and drivability problems cease to exist.

I am wondering if anyone else doing a complete UIM/LIM system rebuild see a specific gasket failure that was causing an intermittent lean code? The 95-97 duratecs are the only motors w/ the fuel rail to intake manifold seal.
Or if the problem was with an injector o-ring? I was trying to search for some posts that had some pics of the gaskets that were replaced.

Has anybody had this similar problem? And what did you find the problem to be?