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2002 Ford F150 Multiple Misfires: P0305, P0306, P0308, P0316, and P0174 - Diagnosis and Fixes

Model: 02 f150 Fault Code: P0174 Posted: 2009-09-19 14:24

Hello everyone, I'm looking for help with a persistent issue on my stepfather's 2002 Ford F150. Recently, the truck started running very poorly without any prior warning signs or stored diagnostic trouble codes (DTCs). It was previously running fine. I've already replaced the crankshaft position sensor, but the problem persists. The vehicle has accumulated 116,000 miles and hasn't seen regular maintenance. There was a past issue with windshield leakage that may have affected the GEM module — this has since been resolved by cleaning a ground connection on the left kick panel. The current diagnostic trouble codes are P0305, P0306, P0308, P0316, and P0174. These indicate multiple cylinder misfires and an initial engine start-up failure (P0316), along with a lean air-fuel mixture in the exhaust system (P0174). I don't have access to a professional scan tool or shop manual, so I'm trying to identify common fixes based on community experience. Given the age and mileage of the truck, I suspect issues related to ignition components, fuel delivery, or vacuum leaks. I’m considering checking for coil terminal corrosion, inspecting intake manifold gaskets, vacuum hoses (especially the 90-degree elbow near the throttle body), and testing spark plugs — though I'm concerned about potential head threading issues in older models like this one. I’ve heard that some 2003+ F150s have modified cylinder heads to prevent plug spitting, but my truck is a 2002 model, so I’m cautious about needing helicoil repairs. Any advice on where to start or what components are most likely at fault would be greatly appreciated. Thanks in advance!

Related fault codes

P0174P0305P0306P0308P0316

Comments (6)

Anonymous 2009-09-19 14:38

I recently researched P0316 and found it indicates a failure during engine startup, which is consistent with the sudden onset of misfires across multiple cylinders. This code often points to ignition system issues or faulty sensors rather than just one component. I plan to swap out the spark coils next and inspect for corrosion in the fuse panel — especially since past water leaks could have caused electrical damage.

Anonymous 2009-09-20 08:43

Check and clean the Mass Air Flow (MAF) sensor. Also, thoroughly inspect all vacuum lines including the intake snorkel, PCV hose, and intake manifold gaskets for cracks, holes, or disconnections. The 90-degree elbow near the throttle body is a common failure point — don’t overlook it. A vacuum leak can cause misfires and lean conditions like P0174.

Anonymous 2009-09-20 12:12

I inspected the affected cylinders and discovered significant corrosion at the coil spade terminals where the spring contacts them. Cleaning these terminals eliminated all but one misfire. I suspect the truck never had spark plugs installed — this may have led to poor grounding and ignition issues over time. I’m hesitant about helicoiling due to access challenges on rear cylinders, especially since my 2002 F150 predates the head thread modifications seen in later models. I’ll also check for vacuum leaks, though I don’t hear any, and have MAF cleaner available for use.

Anonymous 2009-09-23 10:59

I’m wondering if anyone knows the recommended primary and secondary resistance ranges for spark coils on a 2002 F150. I’ve already checked the existing plugs — they’re original — so I’d like to test the coils before replacing them. This could help determine whether faulty coils are causing the misfires.

Anonymous 2009-09-23 15:50

I don’t have exact specs offhand, and resistance testing is not a reliable method for diagnosing coil failure — a coil can have proper resistance but still misfire. On high-mileage trucks with poor maintenance, many mechanics recommend replacing all spark plugs and coils together rather than chasing isolated misfires. This was especially common on older F150s where ignition components were prone to wear. I’m not a fan of Accel ignition products — multiple reports exist about coil failures in their systems. For reliable aftermarket options, Summit Racing or Jegs offer better alternatives.

Anonymous 2009-10-02 12:52

After troubleshooting, the issue was resolved with new spark plugs and cleaning corrosion from the spade terminals on several coils. While changing the plugs was a bit tedious, it wasn’t as difficult as I feared. I also confirmed that some of the original coils were failing due to terminal degradation. I agree — Accel ignition products have had reliability issues in user reports, and I’ve seen multiple cases of failure with their coils.