I'm used to measuring primary and secondary coils for resistance to check, but these thing I'm not sure how they work or how to test them as they only have two terminals. I've searche for about a half hour but am unable find information on how to check and what the measurements are supposed to be. (98 5.4L) Can anyone provide info or links to info?

 

hey dude, i went through the same thing with mine when i had them replaced. the right guy to talk to is tjk_in_cny, he helped me out with my stuff. i looked it up in my book and the primary resistance should be 0.55 ohms and the secondary should be 5500 ohms, and that's for EI systems with Coil Over Plug (COP) which i am assuming you have. put each of your leads on the two prongs inside the plug itself and that is one resistance (primary i think) and then put one on a plug prong and the other on the spring inside the boot and that's the other. if anyone has other comments or if something i said is wrong, speak up!

 

Thanks, your right on everything in your post even your assumptions. My measurements were 5180-5380 on all my coils. I can't measure half an ohm, so I'll call them good as they all have continuity on primary as well. I think my missing problem is sparkplugs anyway, I just wanted to double check everything while I had it appart. Now I gotta find a pintle cap for the injector I dropped on the floor.

 

Those are hats, you can get a set at Auto Zone. Might as well get some O- Rings while your at it.

Secondary resistance fails under a load , it's called a low grade misfire. There's absolutely NO way to test unless you have the Rotunda kit from Ford. Called the WDS kit. You bench "stress" test with this kit.

Or you can look into cylinder history counts to find a weak coil.

It's cheaper spending about $85 on a completely new set of coils/ replacing them and being do with it.

 

Thanks, I looked online at autozone but guess I don't know what to search for... cap or hat doesn't turn up anything. I'm going right by there tomorrow night, so I'll stop in and see... if they don't have, I'll have to stop at the dealer parts dept. and see if they have which also happens to be right beside my destination. So hopefully I'll luck out on one of the two.

I think I skimmed a TSB on this somewhere. More than I think I need to get into right now.

I can do this after I get her all back together and run for a while as I have a data reader/logger)

I'm sure your right. I'm pretty sure after reading on here a fair bit that my plain autolite spark plugs are to blame that I just replaced about 25K or so ago.(yeah I know, platinum... wish I would have found this site before I attempted a simple 5 hour spark plug change... I probably would have sent it to the garage). All the gaps have worn considerably out of the .052-.056 spec under the hood, All are well over .060.

Coils that concern me yet are #3 & #6 as the boot has a very different look... I think some call it carbon tracking maybe. Smell is way different too.

Now that this will be the second time changing plugs (even though I'm cheating this time... changing intake gaskets too), I think it won't be much work to change coils if I have to at a later date.

 

I went thru these problems before, it's a hair puller. In short, do this -

Hats - Just stop by the supplier
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Intake gaskets - Make sure you get the 98 truck engine gaskets. The moved the dowel pins/head holes (locations) around allot. Early and Late models differ.

Order Felpro's From Rock Auto online, you'll get the right ones - The Best.
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Auto Lite doesn't have a Ford Spec plug for your engine. Period!

Purchase Motorcraft. Honeywell = Mother company of Autolite and Motorcraft. Motorcraft = Ford Spec ( Ford heat range) / Autolite = Not Ford spec (wrong heat range)
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Coils = Ebay stores to purchase DG508's

Global Auto or Uneek Supply.
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Replace all at once for ignition integrity - It makes a difference, short and long term. Grease them up correctly to focus ignition to plug.
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Don't think that I'm right, be a little more confident with that and she'll purr like a kitten

Good Luck

 

Yea, those are base. Those tell you if a coil has Primary failure via Multi Tester - It's to bad those numbers or some that vary can't tell you if a coil is functioning properly. Resistance can be higher. While the manual instructs to replace coils with differentiating values, it's not necessary. Coils without readings would indicate failure to the Primary which isn't all that common. I'll see if Tim would like to comment.

 

Everything you stated is correct.
Well done Grasshopper.

I love my Fluke multi-meter..................

There is a little more to it though. (Brew has pointed it out in his reply's).
The problem with manuals sometimes is that they give you a measurement, but do not give you a (+/-) tolerance value. In this case it's measuring resistance. Our manuals state that the primary resistance should be .55 ohms and the secondary should be 5500 ohms (or 5.5 K ohms) but give you no low or high end measurement. That is where you have to know (or guess) what is too high or too low. Out of the 8 COP's I installed on my truck last year, not one of them measured 5500 ohms. They read anywhere from 5100 to 5350 ohms. (with the exception of one, found that out the long/hard way).
My primary resistance measured a tight tolerance of .54, .55, .56.
My point is, I didn't know what the tolerance should be on the secondary measurement but I felt that I could install them knowing that the measurements where about what the manual spec'ed them to be. I did have one coil that was no good from the box and if I had taken the time to measure them all prior to installation, I would have avoided pulling a DOA off the #3 cylinder. I don't remember the ohm reading that I got, but it was way off from the other 7.

Last month, I diagnosed a problem on my Mom's Jeep with the inline-6 cyl.
It was shaking, choking, puking and then the CEL came on. My scanner told me #1 cyl. misfire. Doing all of my normal checks 1st, I then decided it had to be the injector itself. I didn't have a manual for her Jeep but I ohm'ed the connector pins on each injector and found that the #1 cylinder was reading way different from the rest. Ran to NAPA with the bad injector and my multi- meter and compared it to a new one from the box. The new injector measured about the same as the other 5 that were still in the Jeep. I called a service-tech, friend of mine at the local Chrysler/Jeep dealership and he confirmed that the readings I got were correct. Jeep runs great again.

Honestly, I don't understand what bench test Brew is talking about. I have a COP that is measuring .55 primary and 5280 secondary but Brew has explained to me that there may still be an issue with the coil because it was misfiring due to a heater-core hose leak on my #4 cylinder. I cleaned it up, it still looks new, ohm'ed it, it meas. ok, put di-grease back in the boot and it sits in a box as an emergency spare.
My bench test will be, when I am working on the engine next time, I am going to put that Cop/coil on the #1 cylinder and see how it runs. It will take me less than 10 minutes to do. If it's firing ok and my truck runs good during a long test drive, I will pull it,box it, and keep it for a spare.
Actually, my friend AJ, who owns his own shop just called me the other day and asked if I would get him a set from Uneek. I should buy 2 sets of (8) and buy a set for myself. Then I have no worries and I can junk the one that had coolant dripping on it.
OK Long story over......


Good seeing you back on here Skybound !!! I have been crazy busy lately and not spending much time on here. Brother Brew got a hold of me and straightened me out.

TJK

 

I agree, 100%...
If your already in there working, and the COP's havn't been changed, get on Ebay and have a set shipped.

 

One last thing, before I joined this forum, I pulled the bone-head move and put in Autolites. They got pulled 3000+ miles later. I put new MC Plats in with new COP's. Truck runs awesome.

 

Does anyone know how to test primary and secondary on a coil pack for a 97 f150 4.2l?

 

To tie this thread up, consider this.
You can't tell much of anything about these coils with resistence measurement except an outright failure that would show it'self with a failed cylinder code and missing, without testing any coils.
What you had was a coil with shorted turns that reduced the output enough to fail to fire very lean mixtures.
Seldom can anyone detect this with a simple meter since the 'whole' winding is not electrically shorted but is 'magneticly shunted' by the effect of the shorted turns affecting the step up voltage ratio.
There is alot more to the whole thing but this is enough to show it's effect.

 

Hey Bluegrass,
I do understand what your saying and it makes sense to me. I would like more info and detail tho.
Do you have a website in mind that I can go to and read up on the complete workings of the Coil (over plug). I am one of those people who like to learn as much as I can about anything, especially when it comes to engineering and mechanics. I would appreciate it.
I have done some research but nothing that gives me great detail.

Thanks,
TJK

 

What I am referring to is the operating conditions that show up a defective coil.
Consider the following; in overdrive and light throttle, the EGR is called to open under the direction of the PCM program.
When this routine is entered, three major things happen.
1 the ignition timing is advanced.
2 the fuel injection amount is reduced.
3 the EGR meters exhaust gas into the intake air stream.
The result is a very lean air to fuel ratio as high as 20 to 1.
This A/F ratio requires much higher coil voltage to fire the lean mixtures.
Needless to say a defective coil with lower output will missfire under these conditions.
As a side note, the timing is advanced because the very lean mixture flame speed becomes very slow and has to be ignited much earlier for the same completion time point after top center. This also helps fuel mileage along with reduced fuel injection.
As soon as the A/F returns richer, it is easier to fire and the coil acts as normal until the next time the conditions are entered.
Being an intemittant action, the PCM fault recognition program cancels fault reporting because it is now absent. This being the case, there is no code to ID the cylinder involved for easy ID unless a scanner is used to look at each buffer memory location for each cylinder. A code reader will not do this.
At any other time the mixture is rich enough that no missfire occurrs.
Sometimes there are other side efects of this situation such as a violent jerks that resemble complete mommentary power failure to the PCM but returns back to normal running.
What this is thought to be is an interference signal getting back into the PCM that stops signal processing for an instant until the processor recovers and continues normal processing of program information.
As far as the coil goes, it is a winding on a round torroid form. Usually the wire is enamel coated. As the coil heat cycles, the winding's enamel coating can rub through where it lays over another turn and becomes an intermittant short that can't be detected by a DC meter test but has a great effect on the magnetic properties of the whole coil.
Now add to this condition erroded spark plugs and poor boots and you have more fun.
Sometimes people get fooled by installing plugs that seem to fix the miss only to return 500 to 1000 miles later after the new plugs show some errosion and are harder to fire again added to the faulty coil.
BTW I have used other makes of plugs with no problem. Matter of fact I use the cheaper grade without the fancy hardend tip metals and change them more often to keep the motor sharper more of the time. It seems to pay in better fuel mileage and in heavy towing performance.
The high priced plugs are part sales tactic to sell the public on long interval service which is true from that point of view on a practical basis due to the effort and cost needed to service them. You take your position on this as you prefer.
On replacement coils; there is no gaurentee that any coil at anytime will not have a problem and issues must be tracked down in the present and not depend on the "I just changed anything 6 month ago" position because the present is not the past.
After market coils can also have the same issues standard or high performance, makes no difference.
Put the check in the mail please. You won't hear all this anywhere else.
Good luck.

 

- He's right, you won't hear that anywhere else, I even saved this one,- Great info Blue.
Actually, I have a few writups saved from Bluegrass