Why do the V8 coils fail? A few thoughts...

Deaconblue

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Have you ever wondered why the V8 ignition coils fail so often and if there was anything anyone could due to reduce the failure rate or likely hood of them failing?
Well let’s first look into why these ignition coils fail in the first place – beyond of the obvious reasons of improper design or manufacturing as well as oil contamination or water in the spark plug wells, the most likely cause is heat. Now it is really impractical to just remove the covers to reduce the heat because the spark plug wells would soon fill with debris. But there are other ways to reduce the heat, especially the heat generated inside the coils themselves.

As the spark plug ages the gap widens due to normal erosion – even on a double platinum spark plugs. This leads to an increased voltage requirement being need to ionize the atmosphere inside the chamber - to jump the gap and to create the required arch (spark) inside the combustion chamber. That increased voltage requirement demands more current flow (amperage) through the primary winding inside the coil. This increased current flow also produces more internal heat which over time can overload the primary windings, leading to insulation breakdown, shorted out windings and a failed coil.

So if a wider gap requires more voltage to create the spark, which in turn requires more current flow and produces more heat, then conversely a narrower gap would require less voltage, less current flow and lowers the internal temperature of the coil – prolonging the life of primary windings. The stock gap setting on the spark plugs is 1.0-1.1mm (0.039” to 0.043”). Maybe this is just a bit too much for the coils. So what if you were to reduced the gap down to around say 0.9mm or 0.032” to .036”. True it’s not much of a change, but it could have a fairly welcome impact on coil life and not cause any ignition-ability or emissions issues inside the combustion chamber.

Another thing to keep in mind is that a medium wire width (0.4-0.6mm) Iridium center electrode spark plug requires less voltage to create a spark at the same gap and chamber load conditions as does a wide width Platinum center electrode spark plug. Plus these medium wire width Iridium spark plug last just as long as the wide width double Platinum spark plugs. Racers love the very fine wire Iridium spark plug, but they do not last very long in a street engine.

So maybe if you would switch from an Autolite APP3924 to say an Autolite XP3924 or NGK 5464 or Bosch 9603 spark plugs and then carefully (with the correct spark plug re-gapping tool) reduce the gap down to 0.9mm from the normal 1.0-1.1mm range, you just might get these V8 coils to last longer.

I know that’s what I am doing soon.
 
I know everyone complains about coils and maybe I am the exception, but I've averaged over 50,000 miles on a set of coils before even one of them started failing. In fact, I bought the car at about 40,000 miles and didn't have any coil issues until about 100,000 miles. Yes, Motorcraft coils are expensive, but 400ish bucks every 4-5 years for coils and plugs doesn't seem too bad to me. There are many people that go much longer without coil issues and I'm not sure going against manufacturer specs is the best idea to save a few bucks.
 
My car went 10 years before it need new coils. How long are you going to keep your car? Just pony up the several hundred and forget about it. Or let Ford pay like I did with that extended warranty program that many LS owners aren't aware of.
 
It used to be necessary to do a 'tune up' every ten thousand miles. One replaced the plugs, points and condenser and it might also be necessary to do the cap and rotor as well.

As part of my preparation for ECTA racing at Maxton, NC I put in a set of plugs and was one of the pioneers in the use of Mustang plugs by Accel. This was at about 80K and was the first attention I paid to the ignition on my car. I thought it made sense since I proposed to not only run 116 race gas, but a combination of methanol and nitrous oxide as well.

It worked great and I set four records in two different classes all on the same day.

I still have the same plugs and coils I put in at 80K. I now have just north of 150K on the engine.

I, too, believe that heat is the enemy of the coils and have not used the covers since I put the Accel coils in place. This has caused no problems.

KS
 
I did the Accel conversion but modified to fit under the stock covers. Used NGK iridium BKR5EIX plugs and they've been running great since. that was a little over a year ago and 30K-miles later. No issues, complaints, or other things to report. They just work.

So I second Accel coils and NGK plugs. Iridium are better 'performing' plug then platinum at the cost of life span. Copper is still your best 'performing' plug but has the worst lifespan. OEM's like platinum cause they can get 100K-mi on a set which out lasts their warranty. Less maintenance means more money and cheaper cars. So instead of getting 100K-mi on my plugs i'm expecting more like 70K-mi or so. In another few years I'll pull it all out and check it. Somewhere around 130K-mi.
 
If you think heat is the problem, make a plaster cast of the coil area then use it to have a set of aluminum valve covers machined for it. Put a 1MM cover over the coils for a bit of spacing between the coils and the cover. This will let you slather on some heat sink compound between the covers and the coils. This will suck quite a bit of heat off the coils in most situations.

Alternatively, use ducting to run air from the front of the car to the front of the valve cover, with a vent at the back of the cover. You can put a filter in front to keep debris out of the tubes. Then, airflow as the car is moving will flow through the valve cover area keeping the coils cool.

Or, just replace them every few years. If I were planning to keep my LS, I'd be seeing what it would take to fit a set of Chevy LS truck coils to the engine of my LS. Those things are based on the same design used in the old Vortec truck engines, and one of those coils would drive a V8 for about 100K miles firing every cylinder. This means the new coils should in theory last 800K miles or longer as they fire once every other crank revolution instead of four times every crank revolution. A set of plug wires designed for a car with the plugs going into the valve covers, like a 2000ish Corolla uses, could be used on the Lincoln's coil cover to allow the spark plug area to be protected by the elements while allowing the coils to be mounted on the outside where they can get some airflow. Done right, it could actually accent the engine bay.
 
I had my car at the dealership on Friday due to a misfire and he spoke about the coils. He said the new coils are much better than the old motorcraft coils but he told me that if I change the plugs to make sure and use Motorcraft plugs. I had planned on using NGK Iridiums is that a bad idea? I asked him about my coils and he said although some are motorcraft and some are other generic brands he said the coils seem fine. My issue was that I had some water get in there and he sadi I have the wrong plugs in it I guess the previous owner used something else. So what's everyone's opion NGK, Autolite, Motorcraft?
 
I had my car at the dealership on Friday due to a misfire and he spoke about the coils. He said the new coils are much better than the old motorcraft coils but he told me that if I change the plugs to make sure and use Motorcraft plugs. I had planned on using NGK Iridiums is that a bad idea? I asked him about my coils and he said although some are motorcraft and some are other generic brands he said the coils seem fine. My issue was that I had some water get in there and he sadi I have the wrong plugs in it I guess the previous owner used something else. So what's everyone's opion NGK, Autolite, Motorcraft?
NGK Copper.
 
he said the coils seem fine.

did he actually test them properly or was he just going off of how they looked?


also heres the good one, since you had water in the plug wells, did they fix the problem that let water in there in the first place? (its a known problem that the seals on the cowl need to be replaced which divert water to other places...)

if there were two "no" in those answers, try to find a different dealer...
 
He didn't test the plugs to my knowledge. He asked me if they engine had been washed recently and it had ben when they fixed my thermostat housing. So I should check around the cowl as well then? Andhe was just basing the wrong spark plug based on it not being motorcraft. And no other dealer nearby lol. I have already bought the NGK Iridiums and had planned on putting them in regardles of how the old ones looked I just was wondering if its a mistake and I should use a different plug.
 
He didn't test the plugs to my knowledge. He asked me if they engine had been washed recently and it had ben when they fixed my thermostat housing. So I should check around the cowl as well then? Andhe was just basing the wrong spark plug based on it not being motorcraft. And no other dealer nearby lol. I have already bought the NGK Iridiums and had planned on putting them in regardles of how the old ones looked I just was wondering if its a mistake and I should use a different plug.

He's a bit uninformed. When I replaced the plugs on my wife's LS; bought new off the showroom floor with ~15 miles on the odo; half were Motorcraft and half were NGK....... FROM THE FACTORY!!!!!

I use NGK Iridium wit no issues. They last just as long as the platinum. I would stay away from Bosch. The LS doesn't like Bosch very much......
 
Why assume it's external heat causing the failure of the epoxy. Maybe it's internal heat; as in the assembly itself can't dispate heat properly. If that's the case, no amount of external cooling will help.
 
Why assume it's external heat causing the failure of the epoxy. Maybe it's internal heat; as in the assembly itself can't dispate heat properly. If that's the case, no amount of external cooling will help.

Not quite. Heat seeks to equalize, and heat can be moved. When the temp differential between the inside of the coil and the outside environment is increased, heat will leave the inside of the coil faster. This would keep the internal temp of the coil cooler, and if the suspected epoxy breakdown is heat related then it would extend the life of the coil.

I wonder if a computer system water cooler system could be adapted to cool the coils?
 
Lots of things could be tried, but at my current failure rate, it doesn't make sense for me to try any of them.
 
Not quite. Heat seeks to equalize, and heat can be moved. When the temp differential between the inside of the coil and the outside environment is increased, heat will leave the inside of the coil faster. This would keep the internal temp of the coil cooler, and if the suspected epoxy breakdown is heat related then it would extend the life of the coil.

I wonder if a computer system water cooler system could be adapted to cool the coils?

COLD AIR COILS!!!! i can see it now!
 
Lol!
So I started to replace my plugs today on my LS what a pain and I have only done the pasenger side so I am sure I am in for a treat on the driver's side as it looks even tighter. Upon removing the plugs today 4 of them I had 2 NGK Iridium pugs, 1 Autolite Platinum plug and 1 Bosch Platinum plug and 3 different brands of coils in my car lol. I replaced all four plugs and coils although I didn't buy high end coils they are new on the passenger side. Lots of water had gotten unde the cover I can see there was rust on the exterior of the plugs that I removed. I have now put in 4 NGK Iridiums but still having misfire issues so I will attempt the drivers side tomorrow if I have time. I hope I am not making a mistake using cheap coils but we will soon see. Can anyone tell me why they say to use o the coil silicone brake caliper grease and dielectric grease? I understand the dielctric grease.
 
... I hope I am not making a mistake using cheap coils but we will soon see. ...

I believe that you did. See most recent example here:
http://www.lincolnvscadillac.com/forum/showthread.php?94558-ETC-Engine-Failsafe-after-Coil-Change


... Can anyone tell me why they say to use o the coil silicone brake caliper grease and dielectric grease? I understand the dielctric grease.

"They" are probably saying to use either dielectric grease or brake caliper grease. They are saying this because usually, the two are one in the same. I have a jar at home that is labeled for both uses.
 
For you guys running NGK Iridium plugs, which model of plug, 5464 or the 7994?

Heat is the absolute bane of all electronics components, doesn't matter whether they are semiconductor or passive components. Slopping heat sink grease to the top end of the coil to a heat sink will do nothing but make a mess. All the goop does is fill in the microscopic scratches in the surface of the sink and component mounting. Too much goop and it actually performs worse.
 
For you guys running NGK Iridium plugs, which model of plug, 5464 or the 7994?

Mine were the NGK BKR5EIX11 #5464. They seem to be running great with no issues but I never ran them on stock coils.
 
It's usually the plug boot that starts leaking voltage and creates a misfire. In my experience is that most misfires can be repaired long term by changing all the the boots and spark plugs as a set. The boots are made by AC and cost about $6/ea. My '03 LS8 has 210,000 miles, and I haven't bought a coil in the last 110,000 miles, but I have changed all the the boots and spark plugs 3 times in the last 110,000 miles.

There's history of PCM's failing fairly often on LS. I'm sure this is related to misfires. Deal with them as soon as possible!
 

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