Help troubleshooting PO172, PO175, PO300 codes

[zieg85]

This is my brother-in-laws 1997 C1500 with a 5.7L.  The truck has 152K on it and runs very good.  Initial codes were PO141, PO161, PO300.  He changed the O2 sensors the codes eluded to and put new spark plugs in it.  I am going to do a leak down test to try and determine if the fuel pressure regulator is holding.  The MAF sensor is going the right direction.  I am also going to look for bad vacuum lines but under the hood looks like a truck with only 10K on it, this truck is immaculate.  I am also going to really give the plug wires a good looking over.  It seems to run really good and no misfiring is noticed.  Is there anything else from the master mechanics on this forum might suggest to look for.  He has a 30 day waiver to get this fixed in order to pass emission test so he can renew his plates.  Any advise would be greatly appreciated.  Thanks in advance.     

[Irish_Alley]

did he clear the codes and try to see if anything changed?

[zieg85]

did he clear the codes and try to see if anything changed?

The original codes were cleared, he did the initial work and the codes were cleared again.  I know he disconnected the battery for 15 minutes as suggested in reading some troubleshooting reading on the web.  I cleared the latest codes last night and they showed back up on the way to work this morning.  He is working 7 days a week and his commute is less than 2 miles.  I am willing to start from scratch just give me something to go on, step by step and I will do it...

[timthescarrd]

I had a p0300 for awhile on my camaro that took forever to find also sometimes threw O2 sensor codes and bank 2 rich codes,  turned out the FPR (Fuel Pressure Regulator) had busted and fuel was being sucked in the vacuum line.  oull the vacuum line off the FPR and see if there is fuel in it.

[zieg85]

I had a p0300 for awhile on my camaro that took forever to find also sometimes threw O2 sensor codes and bank 2 rich codes,  turned out the FPR (Fuel Pressure Regulator) had busted and fuel was being sucked in the vacuum line.  oull the vacuum line off the FPR and see if there is fuel in it.

Thanks I will check that as well.

[VileZambonie]

Disconnedting the battery will not help. Make sure it's properly tuned, plugs are gapped and installed correctly, tune it up and With the engine cold, turn the key on engine off and monitor O2 voltage. Within 2 minutes, the voltage should drop to about 150 mV. Do you have a scan tool or just a code reader?

[zieg85]

Just a code reader

[VileZambonie]

Verify there is 12 volts on the Pink wire and ground on the Black wire to the O2 heater. Do not use an ohm meter, check it live with the volt meter. Test by backprobing at the connector.

[zieg85]

I will check it tomorrow when I get the truck to take a look at it.