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Q: My truck is giving codes P0171 & P0174

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Last week my check engine light came on. I have a Harbor Freight OBD 2 code reader and got the codes P0102/P0171/P0174 on the reader. P0102 was the M.A.F. sensor and was replaced.Erased the codes and test drove approx 30 miles and C.E.L. came back on.Rechecked the codes and P0102 is gone. P0171 & 174(lean bank 1 & 2) keep coming up. Smoke test performed with plenum on & no vacuum leaks. Removed plenum and duct taped glove to throttle body and cut a finger off a glove to place over the hose from valve cover to plenum. Rechecked with some - no leaks. Cold started engine and sprayed carb spray to see if rpm's would rise. Nothing. Visual inspection found nothing as well. Fuel pressure check revealed 35psi with key on,engine not running. With engine running 35-38psi. After turning engine off - approx 20-25 minutes for gauge to drop to zero. Fuel pump or fuel pressure regulator.?I don;t have a live data OBD tool to check fuel trims. Also hard to start after short drive. Have to use starter spray to start and runs fine.

My car has 88900 miles.
My car has an automatic transmission.

A: Hi there. If the engine is running lean, th...

Hi there. If the engine is running lean, then there could be a plugged fuel filter or a faulty fuel pump with loss of pressure. If the pressure is dropping after 20 to 25 minutes, then there could be a problem with the fuel pump check valve. When the pressure is at 0, having a pressure gauge on the fuel rail, check for the pressure to increase as the fuel pump is turned on when the key is turned on.

If the pressure takes some time before it stops, then the check valve in the pump is sticking open. This means the fuel pump should be replaced. If the fuel pressure is measured very quickly, then replace the fuel pressure regulator on the fuel rail. If you need further assistance troubleshooting your vehicle, then seek out a certified technician, such as one from YourMechanic, who can come to your location to determine why the engine is running at a lean condition and suggest the necessary repairs.

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