01 expy 5.4 p0171 p0301 runs rough
Last week our 2001 expedition started running rough during a rain storm. We took it home and parked it for a couple days to let
it dry out. Still ran rough after drying but now had a check engine light. Got codes p0301 & p0171. Resistance tested the coil,
checked the boot for visible defects, tested injector harness and coil harness. All passed the spark plug was white and ash
covered so I replaced the injector and the plug. Ran decent for a few minutes and all our problems returned. Rescaned the
engine and got only the p0171 (system lean bank 1). Changed 7 spark plugs (all but #4 the hard to reach one) and again the
problem is still here. At idle I pulled all the coil wires 1 at a time (except #4) each time the miss got worse so i assume all cylinders
are now firing. Im stuck and almost out of ideas. Can't afford to just blindly throw parts at it.
Well what controls fuel on only one bank of the engine? Oxygen sensor!
The day after I posted this the cylinder #1 misfire returned. Only acting up when hot or under a load. Not acting up when idling. I just switched the coil an plug boot to other cylinders to see if the misfire moves to the new cylinder. Still running rough but no new codes.
For anyone following along, the misfire code followed the coil. I replaced the coil this morning and the truck runs great. Hope this helps someone.
Change the coil pack intermittent spark or damaged boot
P0171/P0174 Diagnostic Theory for Shops and Technicians When a vehicle has the fault code P0171 and or P0174, it means that computer can no longer automatically adjust the mixture between air and fuel. Code P0171 applies to Bank 1 and P0174 applies to Bank 2. Code P0174 mainly applies to V6 or V8 engines because 4-cylinder engines generally have only one bank, though there are a few exceptions. Some of the high performance 4-cylinder and straight 6-cylinder engines (such as those in BMW and Lexus) split the cylinders into groups of two or three and call them separate banks. When the code says that the Fuel System is "too lean," it means that the computer has been adding more and more fuel, which is called Long Term Fuel Trim. Ideally, the Long Term Fuel Trim should be close to 1 to 2 percent. When a code P0171 is set, it means that the Fuel Trim is anywhere from 15 percent to as high as 35 percent compensated. When this happens, the computer knows that there is an improper condition in the control of the Fuel System. The first step in the diagnosis of a code P0171 and/or P0174 is to look at a minimum of three ranges of the Long Term Fuel Trim numbers on a scanner. Check the idle reading—3000 RPM unloaded and 3000 RPM with at least 50 percent load. Then check the freeze frame information for the code to see which range(s) failed and what the operating conditions were.
OBD II P0301 Fault Code Definition Misfire Detected in #1 Cylinder Symptoms Check Engine Light flashing Rough running, hesitation, and/or jerking when accelerating In most cases, there are no adverse conditions noticed by the driver In some cases, there may be performance problems, such as dying at stop signs or rough idling, hesitation, misfires or lack of power (especially during acceleration), and a decrease in fuel economy Common Problems That Trigger the P0301 Worn out spark plugs, ignition wires, coil(s), distributor cap and rotor (when applicable) Incorrect ignition timing Vacuum leak(s) Low or weak fuel pressure Improperly functioning EGR system Defective Mass Air Flow Sensor Defective Crankshaft and/or Camshaft Sensor Defective Throttle Position Sensor Mechanical engine problems (i.e.—low compression, leaking head gasket(s), or valve problems
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