Changed Plugs in 5.0....Interesting find...

[glfredrick]

Ford used two different style plugs becasue of the way the coils fire on the Ex's. the coils fire through the positive side on one bank and through the negative side on the other one. this causes the spark to jump from the electode to the ground on one side nad the ground to the electrode on the other - sort of like the difference between postive or negative ground on a stick welder... The replacement plugs need to be double platinum so that they can fire from either direction.

 

[elkhunter]

I know they usually fire from the center to the tip but I am confused as to how it can fire from the tip to the center. This would mean the spark would need to travel through the head to the plug and then to the center. I would like this explained because, if it is true, a person leaning against the truck could get the spark even with the plug wires hooked up...I think????

 

[glfredrick]

It all has to do with the way the coils are wired. They have two plug wires per coil and one fires from + to - and the other fires from - to + . Why that would make someone leaning against the truck take a shock, I don't know... Same juice flowing through the same wires, making the same loop, just in reverse.

 

[smiley1]

coils fire through the positive side on one bank and through the negative side on the other one.

That is the stupidest thing I have heard in a long time. Why would Ford design it this way? What kind of benefits were they hoping to gain??

 

[glfredrick]

Do your homework... That's the way it works. Stupid or not, I can't say - the work.

 

[smiley1]

glfredrick,

The stupid comment was not aimed at you at all. I have a decent knowledge of engine mechanics and can not think of a benefit for this firing design.

Do your homework...

I dont expect people to search the internet for me. I just thought if someone knew a simple answer to this question that they could enlighten us all.

I feel that this thread has brought to light some interesting facts on how this motor works. This has been a great forum with great people and an outstanding source of information. The next question, logically, is why?

This forum would not go very far if every question is answered with "Do your homework..."

If the answer to the question is so obvious that I should know then I apologize. I am now sorry for starting this thread. I also apologize if I misunderstood your post.

 

[glfredrick]

Sorry if I overreacted to your comments - I don't know why Ford designed the engines to work this way, I just know that they did. Probably (like in so many cases with Ford) an attempt to save money somehow by getting double duty out of a single part.

I did some searching and found a couple articles that somewhat deal with the issues of the Ford type coils. They did see a model year change in about 1998 from multiple plug-type coils to coil on plug style systems - two different animals...

http://www.wellsmfgcorp.com/counterpoints/counterp_v4_i3_2000.pdf

http://www.bgsoflex.com/mjl/mjl_edis_summary.html

 

[smiley1]

I must have been a little too sensitive the other day as those comments dont bother me normaly. I overreacted.

Anyway, the first link talks about normal coil composition and mechanics.

The second link talks about the EDIS system which is operated by a crank position sensor and eliminates spark waste. This is an interesting read, but I could not find info on reverse polarity spark firing unless I am misunderstanding something.

Thanks

 

[elkhunter]

I think I have searched every web site possible trying to figure this out! I guess that when I get the engine back in I will pull one plug at a time and ground the side or the tip and see if I can see any difference. I agree those articles you posted were interesting but nothing about the reverse spark.

 

[glfredrick]

I wish that I could locate the document that I found that explained it, and I have searced for it, but I just can't bring it up.

I am about 99% sure about that issue, however.

 

[Robb]

Brief explanation directly from Ford:

Each ignition coil fires two spark plugs (12405) simultaneously; one plug on the compression stroke and one on the exhaust stroke. The spark plug fired on the exhaust stroke uses very little of the ignitions coil's stored energy. The majority of the energy is used by the spark plug on the compression stroke. Since these two spark plugs are connected in series, the firing voltage of one spark plug will be negative with respect to ground, while the voltage of the other will be positive with respect to ground.