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Old 05-08-2007, 08:13 PM
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Code PO308

Need a little help. My nephew has a 1998 F150 with a 4.6L Triton. He had the code PO308 - misfire on #8 cylinder. He has changed all the spark plugs but still has a bad miss. I tried swaping the #8 spark plug wire with another wire and it still came up the same code. We kinda rulled out it was the plug wire. We switched the coils to see if the it would come up with a different code. Drove the truck - still had the miss but did not set any codes. My nephew said he would drive it around tomorrow and see if the check engine light comes on. I'll recheck it then to see if it comes up with a different code.

Is there any common problems with this type of engine? Can the coils be checked and what would the resistance specs be?
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Old 05-09-2007, 02:31 AM
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I'm not sure of the spec right off, but a good haynes manual has them in it. It could be a fuel injector problem.
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Old 05-09-2007, 09:32 AM
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Yes, Misfire on cylinder 8 im sure. If its very noticeable like within 200 rpms its a type A misfire or if its a less serious its a type B misfire within 1000 rpms which i dont think will trip the knock sensor which will turn the check engine light on if serious enough.
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Old 05-09-2007, 01:59 PM
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I could be wrong, but I think it is a miss-fire count that triggers the mil. If it doesn't miss fire enough the light will not come on, but the computer will still record it. I have noticed while hooked up to my lap top that the miss log recorded a few misses per second, but never had a MIL even when missing so badly I had to shut the truck off.

You might need more than a code scanner to see what's going on.
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Old 05-09-2007, 03:24 PM
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Make sure you don't have a plug wire crossed. When I did it, the truck ran like crap and no code.
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Old 05-09-2007, 03:40 PM
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I have a Autotap system that I was useing but I only have the generic data. Haven't had the extra money the get the enhanced software yet. The engine misses quite a bit but it still didn't even set a pending code. Thats why I was wondering about the coil resistance or if it could be the injector problem.

Double checked to make sure I had the plug wires on the coils correctly and in the correct order.
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Old 05-09-2007, 03:40 PM
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