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New 5.4 coil resistance sub-par.

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Old 02-17-2004, 12:20 AM
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Vehicle: 1997 Ford F 250
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New 5.4 coil resistance sub-par.

I just purchased a new coil for my 5.4 and the measured primary resistance read .425 ohms. The book calls for a reading of .55 ohms and all 4 coil packs on the passenger side (I just changed the plugs on this side today) read from .510-.540 ohms. I don't like the Autozone coil reading that low and just want to know if anyone knows whether I should bother to replace it. It did cure the severe miss and the P 0307 code, but I still feel a slight pulsation in the motor that was not present before the coil went bad.
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Old 02-17-2004, 08:14 AM
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Did you retry the resistance test after a few miles? I have to wonder if there isn't a change in resistance after a hew heat cycles.

Also, did you change the plug? Thw missing the plug is not in good shape. Resetting the computer is a good idea too. The oxygen sensor (on the bank with the problem) was reading that unburned air (higher oxygen reading). The computer to learned to compensate for it and it will take awhile for it to return to normal unless you reset.

After all my talk here, I don't know the answer to your question. I don't use the primary resistance test much except to look for opens or shorts. Does the book give a range? I have found the readings to vary significantly, and not be a problem. However, that theory is kind of blown with your other coils being so close to each other.
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Old 02-18-2004, 02:14 AM
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Book specs

adaycj,

I did clear the codes, and no I did not test the coil after driving, but I am going to change the plugs on that side (already changed the one on the coil I replaced) tomorrow, so I will test the coil again, and I plan on returning it. The book calls for .55 ohms with no variable range, as is found with the standard coil on the smaller motors.

Everything seems to be okay, but I still feel the annoying slight pulsation that I did not detect before. Of course it could be in my brain, stranger things have happened :-) I will post after I get a coil closer to the spec.
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Old 02-20-2004, 01:24 AM
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New Coil in place, again...

I picked up a replacement for the coil I just purchased from Autozone that had the sub par resistance reading, and I got the new one from Advance Auto, and it read correctly from the start. I don't feel the pulsation in the motor now, but I did eventually get a P1151 code while driving about 60 miles today.
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