Hard misfire cyl 3. Scope shows lesser misfire cyls 1, 2 | Ford Explorer - Ford Ranger Forums - Serious Explorations
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Hard misfire cyl 3. Scope shows lesser misfire cyls 1, 2


Well-Known Member
February 14, 2016
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Year, Model & Trim Level
2000 Mercury Mountaineer
2000 Mountaineer. 4.0 SOHC. 2nd owner. 368,593 miles.

Intermittent misfire cyl 3 has turned to semi-permanent misfire cyl 3.

1. Intermittent misfire started a month ago. Codes P0303, P1402, P0171, P0174.

2. Replaced plugs, wires, coil. Used Motorcraft. Didn't cure misfire.

3. Had dealer replace upper and lower intake manifold gaskets. Didn't cure misfire. Brought it back to dealer.

4. Tech who worked on vehicle said his Noid light showed no signal at injector #3, and intermittent signals at injectors 1 and 2.

5. Said he then wiggled injector harness near cyl #2, where harness exits from lower manifold. Vehicle stopped misfiring and ran normal for about 5 minutes before misfiring again.

6. Tech suggested removing upper/lower manifolds and looking for harness damage (cracked, frayed, broken wires). Also suggested replacing injector #3.

8. I said "If injectors 1, 2, and 3 started working normally when you wiggled the harness, then injector #3 isn't the problem. The fuel injection harness, ECU, or PCM is the problem. Can you test to see if there's signal entering the fuel injector harness?"

9. He said if the fuel injection harness was separate from the engine harness, he could test for signal at the connection between the harnesses.

10. The Ford parts guy said the fuel injection harness is integral to the engine harness. So there's no way to easily punch into a connector and test for signal.

My Question(s)

1. What is the common denominator that sends signal to cyl 1, 2, and 3?

2. How do you test that common denominator?

3. Anyone ever have the same problem; hard misfire cyl 3, intermittent but negligible misfire cyls 1, 2?

4. All suggestions appreciated.