Check engine light went on...took to the shop and both O2 sensors showing bad. Reset and about a week later the CE light is on again. This time one O2 sensor. Shop checked the sensors and they are fine.

Now trouble shooting. They mentioned that it is like the engine is running lean and it wants to make it as rich as possible and this is causing the CE light but they are not sure why this is happening. Asked me if I have a chip.

1999 996 C2 with FAB CAI and cat back, no other mods to engine

They tested feul pressure and that seems fine. Tomorrow they might replace the feul pump to see if that could cause the problem.

Anybody have a similiar problem or any ideas would be appreciated?

Thanks in advance

 

First of all, don't let the dealer replace the fuel pump. It is extremely unlikely that that is causing a problem, especially if the car is running well. Why would they even suggest replacing the pump when the pressure is fine? I would first check for vacuum leaks. Hook up your vacuum gauge and see what the reading is. Check intake connections. What are the error codes? Do you have a good scanner that will not only display the codes but also the readings of most of the sensors in the car? If not, you should get one. Cost is less than $250 and will pay for itself the first time you use it. Also, clean the MAF with electronics spray cleaner or carb cleaner.

 

Just a thought - have you checked to make sure the air filter is installed correctly? I had the same problem, and it was caused by the air filter not being seated correctly. It would be an easy check...

 

HOW MANY MILES ON THE CAR?IF IT IS SHOWING TO BE RUNNING LEAN AND CORRECTING FOR IT BY GOING FULL RICH YOU MOST LIKELY HAVE A LEAK AFTER THE MAF SENSOR.I WOULD CHECK THE BELLOWS TUBE ON THE OIL SEPERATOR.IF THIS IS SOFT AND SPONGY REPLACE IT.

 

Can someone recommend a good scanner for a tt? Link?

 

Why would shop reset ECU and not change 02 sensor the first time? How were o2 sensor tested? I doubt any shop do an accurate test of sensor.

I'd just change all the o2 sensors and see what happens.

CEL is telling you something is wrong with 02 sensor. There is no reason to change fuel pump. Go to another shop.

 

Here is a good scanner that many use. http://www.autoenginuity.com/


Secondly, the CEL IS NOT telling you that the O2 sensors are bad. It is telling you that they are operating out of their normal range. This can be caused by several things, including fuel blockage/leak, pressure, vacuum/intake leak, MAF faulty and on and on. Only by looking at the sensor readings can you begin to understand what is going on with the engine; such as, is the problem in 1 bank or both and are the sensors that control the fuel/air mixture all running normally.

 

Thanks mucho.

 

By the way....having a more free flowing exhaust on a NA engine will initially make the car run extremely rich possably causing the O2 sensors to go out of range. Reducing the back pressure gives you the same result as increasing the valve overlap in the engine and causes more fuel/air to be expelled into the exhaust. The computer will eventually adjust for this by reducing the LTFT.

 

Second visit to the shop for CEL showed only one sensor with a problem. Both sensors were checked and working properly.

Codes P 1123 and P 1125
Fuel/Air mixture is so rich that sensing is up to its lean threshold
Fule pressure test OK
Evap canister purge valve operation OK
Performed smoke to locate vacuum leaks - No leaks found

The shop charged me for one hour of labor and suggested taking it to Danbury Porsche to see what they can find in case it could be covered by emissions warranty.

They did find another car with similiar codes in MN that replaced the MAF and then had an engine rebuild of some sort due to other air vavles within the engine.

Any more thoughts?

 

Hook up your scanner and look at the O2 sensor readings and MAF and LTFT. . Then after recording the readings, remove the MAF and clean it and reinstall. Reset computer by disconnecting battery for a few minutes. Drivethe car around for about 30 minutes and take the same readings. Readings without air condtioning on.

 

Thanks.

Can you really clean the MAF without destroying it? My shop was hesitant to try this so it has not been done as of yet.

What is the end goal of this test and why does the AC need to be off?