as the title says,has vortec 5.7l it has 82000 miles on it when i first drove it home the other day it felt loaded up so i drove it about 60 miles at 50 mph and then decided to clean it out on the highway, got it up to close to 100 and let off when i did the service engine light came on and went to limp mode.brother cleared the codes, po131, po151 o2 sensors thought that maybe it could be the gas in the tank where it was an old mans truck and he never drove it much , put heet dry gas in and it seems to be passing a lot of water out the tailpipe.i have cleaned the k+n air filter that was dirty and i have since drove it easy and it dont seem to set codes that way.then i ran another high speed run and it set codes for all the o2 sensors this time probably because i had to drive it 15 miles to get home! i bought the sensors but have not installed them yet. any input would be appreciated .
Those codes are O2 sensor low voltage codes for each bank correct? So the PCM is seeing a lean condition for whatever reason, that is effecting both banks. I'd be checking for some form of vacuum leak or unmetered air entering the system. I believe that once the CEL illuminates with a powertrain code like that, the PCM will go into limp mode, which may explain why it runs differently once the CEL has illuminated.
STFT = Short Term Fuel Trim, LTFT = Long Term Fuel Trim. In a nutshell it uses feedback from the emission control system to adjust the amount of fuel sent to the engine to maintain an "optimal" air/fuel ratio and lower emission output. The LT is coarse ( measured and adjusted over a longer period of time ) and the ST is fine ( nearly real time ). A plus (+) indicates the computer is adding more fuel than would normally be required and a minus (-) is removing. The LT gathers data and acts as the baseline or standard while the ST makes corrections based on a variety of outside conditions and engine operation ( cold, hot, poor fuel, rain, etc ). Target your trims to +/-3, with the blower I would aim for 0 to -3 ( slightly rich ).
Also cold air can cause a lean condition ( denser oxygen concentration ), or a dirty MAF sensor. Start with the simple and clean your MAF sensor and replace your thermostat with a 180". If that didn't help. move on to these few things to do.
1)Inspect the HO2S wire. The sensor pigtail may be in contact with the exhaust manifold or the exhaust system.
2)Inspect the HO2S oxygen supply. An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provide the supply of oxygen. Inspect the HO2S wires and the connections for breaks and for contamination.
3)Inspect for an intermittent ground in the signal wire between the connector and the sensor.
4)Inspect for contaminated fuel. Water near the in-tank fuel pump inlet can be delivered to the injectors. The water causes a lean exhaust and can set a DTC.
5)Inspect the fuel pressure. The system will be lean if the fuel pressure is low.
6)Inspect for exhaust leaks. An exhaust leak near the HO2S can cause a lean condition.
7)Inspect for vacuum leaks or for crankcase leaks that can cause a lean condition.
8) A sensor pigtail may be mispositioned and contacting the exhaust system.
9) An intermittent short to ground in the signal circuit between the PCM connector and HO2S
10) A poor PCM to the engine block ground
11) Any lean injectors. Perform the Fuel Injector Balance Test.
A poor connection
Rubbed through wire insulation
A broken wire inside the insulation
If the above components are OK, the HO2S may be at fault.
Good luck and keep us posted.
