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Testing for a bad coil pac??


Old 11-11-2004, 07:40 PM
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Location: Cypress, Texas, USA
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Testing for a bad coil pac??

Hey guys,

I would really appreciate your help on this one. I believe I have a bad coil pac, because my truck is acting the same way it did a few years back when I had one go bad. That was under warranty. That being said, I am trying to save some money by fixing it myself. My question is does anyone know how to find out which one is bad using a multimeter, and where to put the connections. I've tried the search, but no luck on actually testing them. Once again I would appreciate all of your help and thank you guys in advance. Kev
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Old 11-11-2004, 08:16 PM
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Location: NH
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You will need to remove the coil (COP). You will need to make two resistance measurements, one for the primary side and one for the secondary side.

The first measurement is for the primary side of the coil. Where it connects normally to the connector will be two connections or terminals you will need to measure across, this if for the primary side. Connect your meter leads to the (+) and (-) terminal. The resistance should be somewhere in the neighborhood of 0.55 ohms.

The secondary measurement will be from the (+) terminal and the terminal that is connected to the spark plug when it is on the truck. This measurement should be in the neighborhood of 5,500 ohms, or 5.5M ohms.

If either measurement shows 0 ohms or “overload” “OL” “999.999” or what ever your meter reads when there is an open the coil is bad.

What may be a good idea is to take two coils off then you can compare the readings you get.
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Old 11-11-2004, 08:20 PM
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You may not need to remove your COP. I would unplug it and take the primary reading across the two terminals. If it is 0 or an open reading you would at least know the primary side is open. However I would mention that the most common side of the coil to go out is the secondary side (the high voltage side) and that is the side you have to measure from the (+) terminal that plugs into the plug by the fuel rail and the terminal that is connected to the sparkplug itself.
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Old 11-12-2004, 09:36 AM
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Location: Ann Arbor, Michigan
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It seems to me that the OBDII should be able to tell you which cylinder isn't firing as well as the others.

My brother, who is VERY good at Ford computers, couldn't find it with all his testing equipment. It only broke down under load and all the coils tested fine without the engine running. He finally took a coil pack off a new engine and we started swapping it out and running the engine until the problem went away. It took about 4 hours by the time we replaced the test coil where we borrowed it from and got a new one for my truck installed.

Last edited by DHFerguson; 11-12-2004 at 09:41 AM.
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Old 11-12-2004, 02:00 PM
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Join Date: Jan 2000
Location: Medina, OH, USA
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I would be willing to bet that the coil pack in question is the furthest back on the passenger side. This seems to always be the one that fails. If this is indeed the one, check the coolant hose connections all around it. Ford had a problem with hoses not being tight, and some moisture would get in the coil packs fouling them up.
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Old 10-03-2007, 12:59 AM
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Join Date: Oct 2007
Location: LAS VEGAS
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funny you say that because i just got mine back from the dealer after finding out the outrageous amount they wanted to charge me for it. i told them to put it back together and ill fix it myself, i brought it in and told them its putting out codes p0301 and p0305.. they tested everything and said that they would replace all 8 plugs and boots and that cylinder 4 had a bad coil pack.. go figure . the hardest one to get too. and i thought i was getting off lucky by having 1 and 5 misfiring. but after hearing all this about leaks im gonna check the hoses.. the desert isnt very friendly with stuff like that.. depending on the price i can find i might just change all 8 coil packs
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Old 10-03-2007, 01:58 PM
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I've had to replace #4 twice in the wifes expy.. It did thro a code also...
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Old 10-03-2007, 03:18 PM
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Location: Lexington,SC
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The only way to Dynamically test the cop(s) is with the OBD port.
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Old 10-03-2007, 05:06 PM
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Location: Florida
Posts: 463
Here's a cop tester that's used with everything in place and running.
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