Hi to all,
I bought my 2006 Rainier 4.2 I6 in 2012 with 70k miles. Initially, the fuel economy was pretty good at 16 MPG. Three years and 25k miles later my mileage was as low as 11 MPG in the winter and 14-15 MPG in the summer. I then started getting the dreaded P0171. I purchased a wifi obdII connector for $25 on amazon and torque app for $5. My LTFT (long term fuel trim) was over 30 when towing which triggered the P0171. Did some internet searches and went after the probable causes: Vacuum leaks, fuel pressure, MAF sensor, burnt exhaust valve. The vehicle still drove ok, but you could tell the idle was slightly erratic, transmission shifting was not as crisp as usual, just didn't feel 100% right.
Steps taken:
1. Tightened intake manifold gasket bolts to spec. They were all loose.
Result: LTFT improved a little. Cost was $0.
2. Performed a smoke test to check for vacuum leaks in the intake system. Used my Halloween smoke machine, worked well, but found no leaks. Cost was $0.
4. Checked spark plugs for any discolouration or proof of poor combustion. A leaking exhaust valve would affect the spark plugs. All were clean and in good condition. Replaced anyway since they were close to 100k miles. Cost was $60.
4. Bought a fuel pressure gauge on amazon and tested the fuel pressure using the schrader valve near the alternator. Tested good at 60 psi. Did not lose pressure with engine off. Cost $60.
4.Added Gumout fuel system cleaner to empty tank and filled tank. Ran until empty.
Improved performance and idle. Small improvement in mileage. Cost $10.
5. Replaced thermostat. No OBDII code set. Based on torque app my motor was running at 185 degrees. After new thermostat engine was running at 205. Gauge in vehicle went from just below mid point to just above midpoint. Based on my experience the vehicle will not lock up the torque convertor unless the temperature is at the max. My rpms were 2100 at 65 mph instead of the normal 1900. After replacing the thermostat my rpms dropped on the highway indicating the torque convertor was locking up again. Cost was $60. Mileage improved a little.
6. Although I did not have an OBDII code indicating the MAF (mass air flow) sensor was failing, I have had vehicles with failing MAF sensor that did not set codes. The MAF sensor can really affect fuel consumption. As high as 20 to 40% so I replaced it anyway. Cost was $80.
Step #6 replacing the MAF had a huge impact, the vehicle idled properly, shifted properly, mileage was up to 17-17.5 MPG. My total cost for all steps was $260. I believe all the steps helped a little, but the largest improvement was from replacing the MAF sensor. LTFT is now in the 5 to 8 range. While 0 is ideal, anything under 10 is considered normal. My vehicle runs like new again and fuel consumption is the best I have had since I have owned the vehicle. Thought I would share my experience for any of you that are dealing with P0171, drivability issues, or poor fuel consumption.
I bought my 2006 Rainier 4.2 I6 in 2012 with 70k miles. Initially, the fuel economy was pretty good at 16 MPG. Three years and 25k miles later my mileage was as low as 11 MPG in the winter and 14-15 MPG in the summer. I then started getting the dreaded P0171. I purchased a wifi obdII connector for $25 on amazon and torque app for $5. My LTFT (long term fuel trim) was over 30 when towing which triggered the P0171. Did some internet searches and went after the probable causes: Vacuum leaks, fuel pressure, MAF sensor, burnt exhaust valve. The vehicle still drove ok, but you could tell the idle was slightly erratic, transmission shifting was not as crisp as usual, just didn't feel 100% right.
Steps taken:
1. Tightened intake manifold gasket bolts to spec. They were all loose.
Result: LTFT improved a little. Cost was $0.
2. Performed a smoke test to check for vacuum leaks in the intake system. Used my Halloween smoke machine, worked well, but found no leaks. Cost was $0.
4. Checked spark plugs for any discolouration or proof of poor combustion. A leaking exhaust valve would affect the spark plugs. All were clean and in good condition. Replaced anyway since they were close to 100k miles. Cost was $60.
4. Bought a fuel pressure gauge on amazon and tested the fuel pressure using the schrader valve near the alternator. Tested good at 60 psi. Did not lose pressure with engine off. Cost $60.
4.Added Gumout fuel system cleaner to empty tank and filled tank. Ran until empty.
Improved performance and idle. Small improvement in mileage. Cost $10.
5. Replaced thermostat. No OBDII code set. Based on torque app my motor was running at 185 degrees. After new thermostat engine was running at 205. Gauge in vehicle went from just below mid point to just above midpoint. Based on my experience the vehicle will not lock up the torque convertor unless the temperature is at the max. My rpms were 2100 at 65 mph instead of the normal 1900. After replacing the thermostat my rpms dropped on the highway indicating the torque convertor was locking up again. Cost was $60. Mileage improved a little.
6. Although I did not have an OBDII code indicating the MAF (mass air flow) sensor was failing, I have had vehicles with failing MAF sensor that did not set codes. The MAF sensor can really affect fuel consumption. As high as 20 to 40% so I replaced it anyway. Cost was $80.
Step #6 replacing the MAF had a huge impact, the vehicle idled properly, shifted properly, mileage was up to 17-17.5 MPG. My total cost for all steps was $260. I believe all the steps helped a little, but the largest improvement was from replacing the MAF sensor. LTFT is now in the 5 to 8 range. While 0 is ideal, anything under 10 is considered normal. My vehicle runs like new again and fuel consumption is the best I have had since I have owned the vehicle. Thought I would share my experience for any of you that are dealing with P0171, drivability issues, or poor fuel consumption.
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