code po 172 keeps coming up! tried to fix it, no luck yet!! on 1996 Chevrolet 2500 Pickup

po172, system too lean bank one, code keeps coming up. i have cleaned the MAF sensor, installed a new air filter, cleaned my EGR valve!! code continues to come up!! any advice? i did all these things one day and the light went off when i was going to scan my truck to see if it was going to go away. now in my process of going to the auto store the light went out!! scanned it anyway and NO codes were shown!!! go figure!!! help!!

by in Bridgeport, WV on December 15, 2011
2 answers 3 comments
ANSWER by on December 15, 2011
Tests/Procedures: 1. Check fuel pressure at idle and under load. Idle pressure should be about 55-57 PSI. Loaded fuel pressure should climb to about 60-65 PSI. 2. Verify the Coolant Temperature Sensor (CTS) is accurate. 3. Check the Mass Air Flow Meter (MAF) for about 4-7 Grams Per Second (GPS) at idle. 4. If all OK, remove the plenum, check for intake "washing" caused by a leaking fuel pressure regulator. Of course you need a scanner that can read serial data to see these specs.
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COMMENT by on December 19, 2011
do you think that i might still have some oily residue built up on the inside of my air cleaner hose? i was using a k&n filter in it and over-oiled my filter. going to clean it out with some brake cleaner and try that too. just curious too, where ion the heck is the coolant temperature sensor located on my truck. never even heard of this!
ANSWER by on December 15, 2011
172 is a rich code, not lean. items like clogged air filters, leaking injector, mass air flow, coolant sensor are some possibilities. you need a shop that can acess the history codes and freeze frame data to see which sensor is reading out of spec and give you a solution. Roy
COMMENT by on December 19, 2011
Roy I think Thor1779 answered his own question. He needs to clean the oil film off the Mass Airflow Sensor. K&N oiled air filters are bad for vehicles that have a volumetric (MAF) fuel metering system. AMSOIL sells a better flowing air filter than K&N and doesn't use oil.
COMMENT by on December 20, 2011
thats why i tell people never, never use those k/n filters. they cause way too many issues. Roy

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