my 2008 impala system rich. i repalce up stream o2 and mass air flow. still get code. any help would be appreciated. thanks bob

 

Put a fuel pressure tester on the injector rail and verify that the system isn't losing pressure. If it is, you may have one or more fuel injectors which are leaking down,causing a rich mixture. If you notice pressure dropping, you can use a wrong side of a hammer to tap the injectors with the handle one at a time to see if the system starts to hold pressure

You could also have a bad signal to the fuel pressure regulator, or a bad regulator itself, causing too much pressure behind the injectors, forcing too much fuel into the cylinders.

 

another thing to check is the flex fuel sensor reading if its a flex fuel vehicle. they can go askew and cause the pcm to overfuel… Check the value in the pcm. If you use regular fuel it should be reading less than 10%. if its over that, reset the sensor reading with the scan tool.

do this vehicle have the stock air intake snorkel?

 

not sure on stock snorkel..

 

check fuel pump presure at rack lost 5 # in 15 minutes.

 

Maybe what you could do is pull your spark plugs and look for evidence that a particular cylinder if getting too much fuel. Black sooty plug, or fuel fouled.

If you are loosing 5 # in 15 minutes, the fuel could be leaking past an injector.

Is the vehicle hard to start in the morning?

I didn't see how many miles are on the odometer, not that it would matter much, but when a hot engine shuts off, the heat soak can result in fuel deposits on the tip of the injectors, keeping them from closing all of the way.

 

96000 miles, i never smell over rich at tail pipe. car runs good.

 

Glad to find that your car, with a P 0172 code, is now fixed.

I think I'm done here.