Mercury Villager (1997) P0305 and P0325 Codes: Causes, Fixes & Diagnostics for 155k-Mile Engine
Hi everyone, I'm new to this forum but have been researching similar issues. I own a 1997 Mercury Villager with approximately 155,000 miles and am currently experiencing two OBD2 trouble codes: P0305 (Cylinder 5 Misfire) and P0325 (Knock Sensor Circuit Malfunction). In the past, a basic tune-up—replacing spark plugs, wires, cap, and rotor—has resolved these issues every 18–24 months. However, this time, even after completing that maintenance, both codes persist. From my research, I understand that fuel injectors or intake manifold problems (such as gasket leaks or port plugging) could be contributing factors. My neighbor, a mechanic, suggested that a leaky injector might cause misfiring—something I hadn't heard before—but I’ve never had injector issues on any of my previous vehicles. I also read that the knock sensor in older Mercury Villagers (which is technically a Nissan Quest platform) is prone to failure. My question: Are P0305 and P0325 related? Could one code be causing or masking the other? Additionally, I’ve tested the knock sensor using the Haynes manual method—disconnecting the connector from the upper intake manifold, grounding one lead of a digital multimeter (DVM), setting it to AC volts, and tapping the intake with a hammer. The meter responded each time, suggesting functionality. However, initial resistance readings were as high as 35 megohms, which is far outside the expected range of 500–620 kΩ at 77°F. After cleaning the sensor’s mounting surface and retesting, the reading dropped to around 540 kΩ. I also performed a fuel pressure test and bleed-down test. The fuel pressure was within spec, but the bleed-down valve in the tank failed the test—indicating potential leaky injectors. Two of the six injectors tested out of range: one with 0.5 ohms (shorted), another at 34 ohms (out of normal 10–14 ohm range). I’ve also checked for vacuum leaks by spraying starting fluid on intake gaskets and hoses—no signs of a leak were found, though the rear section was not fully tested. The engine runs very roughly and is currently non-driveable. I plan to replace the upper intake manifold gasket, clean the EGR system (which wasn’t clogged but was cleaned anyway), and perform a full rebuild including spark plugs, wires, cap/rotor, fuel filter, PCV, and throttle body gaskets. I’m now considering whether to replace the knock sensor or simply fix the grounding issue. Based on my findings, I believe the misfire may stem from faulty injectors rather than a failing knock sensor—especially since both P0305 (cylinder 5 misfire) and P0325 (knock sensor fault) appear to occur together. I’m sharing this experience as a cautionary note for others working on older Mercury Villagers, especially regarding the complexity of disassembling the upper intake manifold and potential corrosion at the knock sensor mounting point. Thanks to everyone who contributed advice—this forum helped me diagnose and resolve my issue step by step.
ant vaccum leaks?