Test Coil
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Joined: Nov 2005
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From: Huntley, IL
Test Coil
Does anyone know of a way to test the coils to see if they are putting out the right voltage?
I have a small vibration at idle and it looks like a bad coil is a common problem.
I have a small vibration at idle and it looks like a bad coil is a common problem.
Tuned
Joined: Sep 2003
Posts: 296
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From: north carolina
Since this is the forum for Expeditions, I assume you are asking about tests for COP (coil on plug)??
The Haynes manual provides a test procedure that checks resistance through the primary and secondary COP circuits. If I remember correctly, check the primary by attaching positive and negative of a good digital VOM to the two connector pins in the plug on top of the COP. The resistance should be 0.5 to 0.8 ohms. Check the secondary by attaching one VOM lead (positive or negative) to one of the top connector pins (either one, I think) and the other lead to the spring end at bottom of the boot insulator (attaches to the spark plug). The resistance should be 5K ohms.
Someone double check my resistance numbers---I don't have my manual handy, and just going from deep memory on this. Been a long time since I checked a COP.
The Haynes manual provides a test procedure that checks resistance through the primary and secondary COP circuits. If I remember correctly, check the primary by attaching positive and negative of a good digital VOM to the two connector pins in the plug on top of the COP. The resistance should be 0.5 to 0.8 ohms. Check the secondary by attaching one VOM lead (positive or negative) to one of the top connector pins (either one, I think) and the other lead to the spring end at bottom of the boot insulator (attaches to the spark plug). The resistance should be 5K ohms.
Someone double check my resistance numbers---I don't have my manual handy, and just going from deep memory on this. Been a long time since I checked a COP.
"Mifflin Clay"
Joined: Jul 2005
Posts: 3,177
Likes: 4
From: Mifflin, PA
Originally Posted by gibsonj
Since this is the forum for Expeditions, I assume you are asking about tests for COP (coil on plug)??
The Haynes manual provides a test procedure that checks resistance through the primary and secondary COP circuits. If I remember correctly, check the primary by attaching positive and negative of a good digital VOM to the two connector pins in the plug on top of the COP. The resistance should be 0.5 to 0.8 ohms. Check the secondary by attaching one VOM lead (positive or negative) to one of the top connector pins (either one, I think) and the other lead to the spring end at bottom of the boot insulator (attaches to the spark plug). The resistance should be 5K ohms.
Someone double check my resistance numbers---I don't have my manual handy, and just going from deep memory on this. Been a long time since I checked a COP.
The Haynes manual provides a test procedure that checks resistance through the primary and secondary COP circuits. If I remember correctly, check the primary by attaching positive and negative of a good digital VOM to the two connector pins in the plug on top of the COP. The resistance should be 0.5 to 0.8 ohms. Check the secondary by attaching one VOM lead (positive or negative) to one of the top connector pins (either one, I think) and the other lead to the spring end at bottom of the boot insulator (attaches to the spark plug). The resistance should be 5K ohms.
Someone double check my resistance numbers---I don't have my manual handy, and just going from deep memory on this. Been a long time since I checked a COP.
Tuned
Joined: Sep 2003
Posts: 296
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From: north carolina
If one of the COPs gets too far out, it will throw a code, usually P030x where x is the cylinder number. Will indicate cylinder misfire.
My experience has been that usually the boot is suspect, rather than the COP. If the rubber deteriorates, it will allow the secondary voltage to "bleed", which can cause a slight "miss" or vibration at idle, and ultimately lead to the computer throwing a misfire code, commanding the MIL on.
While you have the COP out, and particularly if its resistance readings are in line with your others, as Alchymist suggests, then check the boots. If one of them feels more "spongy" than others, replace it. Its about $3 bucks at the parts stores. Especially for cylinders 4 and 8, which are a real bear to get to anyway on the 5.4s.
My experience has been that usually the boot is suspect, rather than the COP. If the rubber deteriorates, it will allow the secondary voltage to "bleed", which can cause a slight "miss" or vibration at idle, and ultimately lead to the computer throwing a misfire code, commanding the MIL on.
While you have the COP out, and particularly if its resistance readings are in line with your others, as Alchymist suggests, then check the boots. If one of them feels more "spongy" than others, replace it. Its about $3 bucks at the parts stores. Especially for cylinders 4 and 8, which are a real bear to get to anyway on the 5.4s.
Tuned
Joined: Aug 2003
Posts: 341
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From: McMinnville
COP's
I am getting ready to change the plugs on my Expy 99 5.4 and because I am a rookie and will depend on all these sites, do I change the COP with each plug, or are there aftermarket COP's that are better than the stock ones?
Freshman User
Joined: Dec 2005
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Today is day 2 of changing the plugs on my 98 5.4. I worked 2hours yesterday and finished more than half. I removed all the COPs and checked the prim and sec resistance. I have one bad #3 COP. (read 12K on seconday), the rest around 6K. I have a cheapie meter so I assume the 6k is going to be OK for the rest of them since they are all about the same. Check more threads for more instruction and tips for these plugs because they are a bear. I had to obtain several extensions of varying lengths, and universals to get to some hard to reach COP bolts and those plugs are buried DEEP as well. One tool that was crucial was the 7mm flex socket from Sears. A Low profile socket that is a must for that #7 COP bolt that is hidden under the fuel rail. I had to loosen my fuel rails for better clearance also. Well I am going outside now to finish the job. Let us know how it went for you!
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Tuned
Joined: Aug 2003
Posts: 341
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From: McMinnville
Do you have a part number for that 7mm socket? Is it the auto swivel 7mm or just the 7mm itself? I will be doing this in the next week or so. Did you buy the same COP (stock) or go with an aftermarket if there are any?
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Senior User
Joined: Mar 2005
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From: Nottingham, MD
Another trick for putting in the new plugs is to get a piece of hose about a foot long, make sure the end fits over the porcelin part of the plug snugly then screw the plug into the head. Once in just pull the hose off.
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Originally Posted by jwhopson
Do you have a part number for that 7mm socket? Is it the auto swivel 7mm or just the 7mm itself? I will be doing this in the next week or so. Did you buy the same COP (stock) or go with an aftermarket if there are any?
I used the swivel 7mm + 4"extension + universal + 4" extension + driver to get to that #7 COP.
I did not swap out the COPs, they were all OK except for one that had a high reading on the secondary. I found some cheap on Ebay, not aftermarket, motorcraft branded. around 20 bucks, I might buy one. The truck is running great now after just changing the plugs, what a difference.
Tuned
Joined: Aug 2003
Posts: 341
Likes: 3
From: McMinnville
Plugs
Holy Cow - that is quite the combo of extensions. I am still a little nervous to start it myself, all the stuff on top of the engine looks so intimidating. Another question - I haven't searched yet but if you get white/black smoke come out of the exhuast when you start the car what does that mean? I am hoping changing the plugs will fix that but not sure.
Freshman User
Joined: Dec 2005
Posts: 29
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Originally Posted by jwhopson
Holy Cow - that is quite the combo of extensions. I am still a little nervous to start it myself, all the stuff on top of the engine looks so intimidating. Another question - I haven't searched yet but if you get white/black smoke come out of the exhuast when you start the car what does that mean? I am hoping changing the plugs will fix that but not sure.
its not that bad with some patience. Dont know bout the smoke though, sounds serious!
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