Cylinder 4 misfire only under extreme load - Taurus Car Club of America : Ford Taurus Forum
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post #1 of 12 (permalink) Old 04-04-2019, 10:22 PM Thread Starter
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Cylinder 4 misfire only under extreme load

1996 taurus OHV 3.0. When climbing a mountain on the highway (70 mph) engine light flashes, and engine misses badly. Upon throttling back, or reaching the top, engine runs normally. ONLY happens under these conditions. Code generated is cyl 4 misfire. I have changed and or tested the injector, plug, wire, and coil.....all are fine. My friend who is a 35 year ford mechanic is stumped....swears it must be electrical. (????) Any thoughts ? Thanks in advance.
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post #2 of 12 (permalink) Old 04-05-2019, 02:49 AM
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Check the coil for cracks and replace if you haven't Also the plug wires.



A compression check on that cylinder will rule out major mechanical issues and since in the front of engine is simple to do.
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Last edited by Automender12345; 04-05-2019 at 02:54 AM.
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post #3 of 12 (permalink) Old 04-05-2019, 09:34 AM
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Originally Posted by kbrown View Post
1996 taurus OHV 3.0. When climbing a mountain on the highway (70 mph) engine light flashes, and engine misses badly. Upon throttling back, or reaching the top, engine runs normally. ONLY happens under these conditions. Code generated is cyl 4 misfire. I have changed and or tested the injector, plug, wire, and coil.....all are fine. My friend who is a 35 year ford mechanic is stumped....swears it must be electrical. (????) Any thoughts ? Thanks in advance.



Sure sounds electrical to me too. When you say 'changed or tested' can you tell us what was replaced vs tested? I think it's probably plug, wire, or coil that is failing. If the plugs and wires haven't been replaced in a long time they are probably overdue anyway.

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post #4 of 12 (permalink) Old 04-05-2019, 10:06 AM Thread Starter
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replaced the injector and plug. swapped wires, but the issue stayed on cylinder 4, so not the wire. put in brand new coil..... issue still there. So... apparently not electrical. Compression is good on cylinder 4 when testing, but no idea if losing compression under load.

Last edited by kbrown; 04-05-2019 at 10:08 AM. Reason: typo
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post #5 of 12 (permalink) Old 04-05-2019, 01:07 PM
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What's your fuel trims look like and are you losing coolant. What did spark plug look like? What was the compression?

Last edited by Automender12345; 04-05-2019 at 04:15 PM.
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post #6 of 12 (permalink) Old 04-05-2019, 06:23 PM
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If I may, I would check the Fuel Pressure Regualtor, a leaking FPR can cause mis-fires. Just my 2 cents.

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post #7 of 12 (permalink) Old 04-07-2019, 08:39 AM
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Initial coil fails will first start to appear on high loads. I had a 89 Blazer that did that. My mistake was a new AZ coil that did the same thing. After pulling out my hair a switch to a Napa coil solved the issue. Motorcraft or BWD coil from Advance would my next step if plug and wire is new as those coil packs are the only good replacement ones.
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post #8 of 12 (permalink) Old 04-11-2019, 01:21 AM Thread Starter
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Originally Posted by Draco911 View Post
If I may, I would check the Fuel Pressure Regualtor, a leaking FPR can cause mis-fires. Just my 2 cents.
thanks, but fpr would cause random misfires, not same cylinder over and over, yes?
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post #9 of 12 (permalink) Old 04-11-2019, 01:22 AM Thread Starter
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Originally Posted by repairman54 View Post
Initial coil fails will first start to appear on high loads. I had a 89 Blazer that did that. My mistake was a new AZ coil that did the same thing. After pulling out my hair a switch to a Napa coil solved the issue. Motorcraft or BWD coil from Advance would my next step if plug and wire is new as those coil packs are the only good replacement ones.
i replaced with a brand new BWD....same issue continued. definitely not the coil.
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post #10 of 12 (permalink) Old 04-11-2019, 01:25 AM Thread Starter
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thanks. compression was in the 140-150 range....a bit less than the other cylinders, but not much. engine has 385k on it, so pretty good compression, all things considered.
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