I have a 2001 Ford Expedition 4.6L V8 and I’m struggling to find out why it won’t start. It had been sitting for a while, so I used my OBD2 reader and saw a P0171 code. After some effort, I managed to get it running by cranking and pressing the gas pedal a lot. It ran for 45 minutes, and I checked the scan tool data; STFT and LTFT were between +20-30% at idle. At 2500 RPMs, the numbers improved slightly but not much. I replaced the PCV valve after reading up on possible fixes, but it wouldn’t start. Putting the old valve back didn’t help either. I cleared the code and disconnected the battery for 30 minutes, but still no luck. I can hear the fuel pump and see fuel at the rail, but it only runs for a few seconds when I use starter fluid. I checked spark on cylinder #1 and didn’t see an arc, but cylinder #2 seemed fine. I couldn’t check the rest due to losing daylight. Could bad coils or spark plugs cause the P0171 code? Or is it more likely a vacuum leak that I can’t find without it running?
It’s easier to check the plugs at night for better visibility. Did you check if fuel actually sprays out when pressing the Schrader valve or use a pressure tester to measure the pressure? P0171 means it’s running too lean, often due to extra air getting in, but it could also be low fuel. You can try a smoke test even without the engine running.
@Sam
Gas came out when I pressed the stem on the Schrader valve, but I didn’t use a pressure tester. How do you do a smoke test without the engine on?
Jordan said:
@Sam
Gas came out when I pressed the stem on the Schrader valve, but I didn’t use a pressure tester. How do you do a smoke test without the engine on?
Just blow smoke into the intake or near the evaporator area to spot major leaks. Also, you need to know the actual fuel pressure. When checking plugs, if they’re dry after cranking, it could mean no fuel is getting through. A smoke test can help find intake gasket leaks too. Don’t forget, sometimes it’s a simple issue. Did you look at the O2 sensor voltage to see if it’s normal? A steady reading isn’t a good sign if the engine is running.
@Sam
Thanks. I’m getting a fuel pressure test kit today and maybe a smoker too. I can test at the port on the fuel rail. My spark plugs look dry but I’ll swap them out while I’m at it. Both O2 sensors show normal voltage between 0.1V and 1V from what I read, so that’s good.
@Jordan
Check the voltage patterns; if you have a digital multimeter or a scan tool with that feature, it’s worth looking into. A flat reading can mean trouble, even if the numbers seem fine.
Check the actual fuel pressure. I had a similar issue with my Mark VIII, needing three long cranks to start. It turned out the pump was only pushing out half the needed pressure. A single bad coil or plug might cause slight vibration without setting codes. My '97 5.4 ran on 7 cylinders and didn’t show a code but did run rough. With multiple bad ones, it shakes more.
@Nori
I tested the fuel pressure—zero before and after replacing the fuel filter, though the pump does make noise when the key is turned to ON. It briefly ran for 1-2 seconds after I swapped the filter but then shut off. Now, nothing comes out of the test port. Does this mean it’s definitely the fuel pump, or could it be the fuel pressure regulator too?
My 08’s fuel pump failed in a similar way without any codes. Fuel was present at the rail but barely had any pressure. After changing the in-line filter, all the remaining fuel dripped out, and we couldn’t get fuel to the rail afterward. Turns out, the clogged filter overworked the pump until it burned out. Even if the pump still runs, it might be too weak. Try changing the filter and plug first, then move on to the pump if needed. A clogged filter or weak pump can trigger a lean code too.
@Fifer
I checked fuel pressure using a gauge on the fuel rail’s port, but it read zero, even though the pump came on. After replacing the fuel filter, the pressure stayed at zero. When I tried cranking, it ran for 1-2 seconds and died. No fuel came out of the test port after that. So, do you think it’s definitely the pump, or could it be the fuel pressure regulator?