Code P0301 and Ocassional P0171 | Ford Explorer Forums - Serious Explorations

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Code P0301 and Ocassional P0171


Well-Known Member
April 6, 2007
Reaction score
City, State
Cape Coral, FL
Year, Model & Trim Level
99' Explorer XLS
Well, my 2000 Sport OHV has been acting up since I replaced the upper intake gaskets, DPFE, IAC, and EGR valves & hoses. Before these replacements, the truck was giving off a P0171 (Lean Bank One) code which is a common problem with leaky plenum gaskets on these trucks. The problem is that now it's throwing a P0301 (Cylinder #1 misfire), and I can't seem to detect the root of the problem.

Parts replaced within the last 6 months:
Both upstream O2 Sensors
Plugs & Wires
Coil Pack
IAC Valve
EGR Valve
DPFE Switch & hoses
Fuel Rail Gasket
Upper Plenum Gasket

I have not replaced the very lowest intake manifold gasket yet, but then again I have not heard any "sucking" sounds indicating any violent vacuum leaks. Injectors were cleaned and pulse tested well. Any ideas on where to go from here???

UPDATE: the hose that goes from under the throttle body (Evap return hose I believe) was completely collapsed and cracked all over. In an effort to start ruling out possibilities and weed out the false alarms, I replaced the entire assembly with tough 3/4 transmission cooler return line hose. The engine runs a tad better, but still getting a P0301 Cylinder #1 misfire. Also, I thought I might add that on my torque app, I read full activity on O2 sensor bank 2 sensor 1, but zero activity on bank 1 sensor 1. Still not sure if that is just my app that is not reading it or not, but I am going to troubleshoot further tonight.

Well, I pulled the lower IM, and found the Gasket to be in pretty bad condition, as well as the intake runners being overrun with gunk. I cleaned everything up and bought a gasket. There were no detectable vaccum leaks from the spray test, but I have seen a lot of people with misfire problems due to the lower IM gasket. Can anyone tell me if this could of been my case by the following pictures?








did you ever figure it out ? i'm on the same boat without paddles