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Whoa thats a lot of damage to that plug. That motor needs to come out before you do any more damage IMO.

FWIW I have been told to never use the Costco fuel in our performance cars. Discount fuel never a good choice for our street machines. I used to think like Goose and anything 93 was good but some much smarter people have told me that not all fuel is created equal. These same people say Chevron/Texaco 93 with Techron is the best fuel for our beasts.
 

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2010 GT500 Super Snake, Kona blue W/white stripes, CSM10SS0012
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Discussion Starter #22
Whoa thats a lot of damage to that plug. That motor needs to come out before you do any more damage IMO.

FWIW I have been told to never use the Costco fuel in our performance cars. Discount fuel never a good choice for our street machines. I used to think like Goose and anything 93 was good but some much smarter people have told me that not all fuel is created equal. These same people say Chevron/Texaco 93 with Techron is the best fuel for our beasts.
A guy at the local Dyno shop said the same about Costco gas, but it’s top tier gas. So I’m not sure what to believe. There’s a sticker by the gas cap from Whipple that says 91 octane minimum. I’m gonna start using only 93 octane if I can help it. For the record, that spark plug‘s ceramic insulator is loose and it moves. If I tilt the plug the other way, the insulator moves away from the electrode. I don’t believe there’s been any physical contact between the piston and the plug. But I’m no expert. These plugs were installed by Shelby at the time of the super snake mod.
 

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So what would cause piston to spark plug contact (if that is what happened)? I know back in the "old days" alum. rods could stretch, but what on our cars would cause such a situation? something got down in the combustion chamber? failure of a rod bearing? <<<but that would be more than a "tap".....it would be a knock.....
Robert, the piston is .1" down in the bore on a 5.4, so when you also consider the dish in the surface of the piston, the POI is probably .2" below the deck of the block. The piston can rise no further than the deck surface of the cylinder head, even with a broken rod. I'd have to think the ground strap on the plug is .25" above the deck surface at the top of the combustion chamber. In effect the bottom of the piston and the ground strap are ~.45" from one another, .35" with a broken rod. So unless you have a foreign object that made it's way to the combustion chamber or a chunk of piston bouncing around the chamber, it's physically impossible, unless it was installed just like that. I have seen porcelain that broke off the electrode bounce around and close the gap, but the plug with the closed gap still seems to be intact. What ever hit that ground strap hit it hard. I'm not sure porcelain could smash it to that extent. It's soft and brittle and is expelled out thet exhaust valve rather quickly, usually with no damage.
 

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A guy at the local Dyno shop said the same about Costco gas, but it’s top tier gas. So I’m not sure what to believe. There’s a sticker by the gas cap from Whipple that says 91 octane minimum. I’m gonna start using only 93 octane if I can help it. For the record, that spark plug‘s ceramic insulator is loose and it moves. If I tilt the plug the other way, the insulator moves away from the electrode. I don’t believe there’s been any physical contact between the piston and the plug. But I’m no expert. These plugs were installed by Shelby at the time of the super snake mod.
It is the crush bent ground that is strange, it does not bend unless it gets touched. The electrode and ceramic insulator is above it, so what pushed it up enough to touch the electrode and dislodge the insulator, if that is what has happened?

Just a thought.......maybe remove all plugs and then rotate the engine manually, then maybe install one plug at a time, properly gapped and try to roll the engine over and see if there is contact? Others will chime in with their thoughts....

R
 

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Robert, the piston is .1" down in the bore on a 5.4, so when you also consider the dish in the surface of the piston, the POI is probably .2" below the deck of the block. The piston can rise no further than the deck surface of the cylinder head, even with a broken rod. I'd have to think the ground strap on the plug is .25" above the deck surface at the top of the combustion chamber. In effect the bottom of the piston and the ground strap are ~.45" from one another, .35" with a broken rod. So unless you have a foreign object that made it's way to the combustion chamber or a chunk of piston bouncing around the chamber, it's physically impossible, unless it was installed just like that. I have seen porcelain that broke off the electrode bounce around and close the gap, but the plug with the closed gap still seems to be intact. What ever hit that ground strap hit it hard. I'm not sure porcelain could smash it to that extent. It's soft and brittle and is expelled out thet exhaust valve rather quickly, usually with no damage.
That is what I was thinking, something foreign........
 

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A guy at the local Dyno shop said the same about Costco gas, but it’s top tier gas. So I’m not sure what to believe. There’s a sticker by the gas cap from Whipple that says 91 octane minimum. I’m gonna start using only 93 octane if I can help it. For the record, that spark plug‘s ceramic insulator is loose and it moves. If I tilt the plug the other way, the insulator moves away from the electrode. I don’t believe there’s been any physical contact between the piston and the plug. But I’m no expert. These plugs were installed by Shelby at the time of the super snake mod.
So there is still a gap between the ground strap and the electrode, when the porcelain moves out of the way? If so, you're probably okay. It looks to us like something smashed the ground strap into the electrode, which would not be a good thing.
 

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Does it have to be physical contact for this to occur? Can detonation cause the spark plug gap to close?
 

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Does it have to be physical contact for this to occur? Can detonation cause the spark plug gap to close?
Pretty much. Detonation, or rather heat from detonation can cause it to melt too. From what I'm understanding now, the strap is not contacting the electrode. The porcelain has broken away from the electrode and is sliding up the electrode to give the illusion that it's smashed by the ground strap. And when I say smashed, it appears that no portion of the electrode is visible, which would have to be a hell of an impact if the porcelain was in fact intact.

I have heard of gaps closing on boosted cars.....Maybe detonation causes an even larger gap closing problem?
Frankly, I doubt that. If that did occur, it would be a miniscule amount. Try closing a gap by hand. It's much harder material than you think and some are much harder than others.
 

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Frankly, I doubt that. If that did occur, it would be a miniscule amount. Try closing a gap by hand. It's much harder material than you think and some are much harder than others.
I have never had it happen to me, but some on these forums have claimed it happens?

I would guess that if the compression is escaping out of the combustion chamber around the porcelain, there would be abnormal ticking sounds from that? Maybe even like an exhaust leak or leaks, but muffled under the coil covers?

R
 

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I have never had it happen to me, but some on these forums have claimed it happens?
Sounds like someone probably didn't gap their plugs beforehand or dropped them down the plug hole and saving face. I've seen gaps open, but that's just the normal wear process. Over time the ground strap and electrode wear out and it increases the gap.

I would guess that if the compression is escaping out of the combustion chamber around the porcelain, there would be abnormal ticking sounds from that? Maybe even like an exhaust leak or leaks, but muffled under the coil covers?
I've never heard of that happening. When the porcelain breaks it's only the portion exposed to the combustion chamber. I've also seen them cracked on the outside, but I think that's from mishandling, not detonation.

Here's where I think the porcelain is broken. Note my red marks. It's just on the inside of the projected tip and can slide up an down the center electrode.

205641
 

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I would say car went lean aswell. not a gt500 but on one of my other cars my boost spiked to 48psi From 36psi and Leaned out Causing every plug to split the porcelain . IMHO Costco gas is the worst lol sorry especially in a performance car.
 

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Sounds like someone probably didn't gap their plugs beforehand or dropped them down the plug hole and saving face. I've seen gaps open, but that's just the normal wear process. Over time the ground strap and electrode wear out and it increases the gap.


I've never heard of that happening. When the porcelain breaks it's only the portion exposed to the combustion chamber. I've also seen them cracked on the outside, but I think that's from mishandling, not detonation.

Here's where I think the porcelain is broken. Note my red marks. It's just on the inside of the projected tip and can slide up an down the center electrode.

View attachment 205641
You may be right on the break area.

OP - Can you confirm how or where the porcelain is broken on your plug(s)? Is it just above the gap area or inside the plug itself?

R
 

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2009 Shelby GT500 Vista Blue/White Stripes
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Sounds like someone probably didn't gap their plugs beforehand or dropped them down the plug hole and saving face. I've seen gaps open, but that's just the normal wear process. Over time the ground strap and electrode wear out and it increases the gap.


I've never heard of that happening. When the porcelain breaks it's only the portion exposed to the combustion chamber. I've also seen them cracked on the outside, but I think that's from mishandling, not detonation.

Here's where I think the porcelain is broken. Note my red marks. It's just on the inside of the projected tip and can slide up an down the center electrode.

View attachment 205641
This is exactly what happened. The ground strap was never hit by anything. It has the perfect curve it is supposed to have from the factory. That piece of porcelain broke near where you show in your picture and slid down and made contact with the ground strap, not the other way around. The OP already said that the ceramic insulator is loose and moves up and down on the electrode which further proves this. Maybe Denso spark plugs are of inferior quality for our engines as well as of course bad gas, detonation or running lean being a contributing factor to the OP's situation. Even BJ recommends NGK, Motorcraft or Brisk spark plugs.
 

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2010 GT500 Super Snake, Kona blue W/white stripes, CSM10SS0012
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Discussion Starter #35 (Edited)
You may be right on the break area.

OP - Can you confirm how or where the porcelain is broken on your plug(s)? Is it just above the gap area or inside the plug itself?

R
I had one where the porcelain on the outside of the cylinder was chipped. Thats what started this whole fiasco. But 3 of the plugs had this issue inside the cylinder where the ceramic piece, that looks like a donut, become loose or went missing altogether. The gap was not closed, it’s just that loose piece resting on the electrode you’re seeing. See the video below.

 

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I had one where the porcelain on the outside of the cylinder was chipped. Thats what started this whole fiasco. But 3 of the plugs had this issue inside the cylinder where the ceramic piece, that looks like a donut, become loose or went missing altogether. The gap was not closed, it’s just that loose piece resting on the electrode you’re seeing. See the video below.

I would try another brand of plugs as I mentioned earlier after you figure out what was the cause. Bad fuel, running lean, detonation or a combination of any of those. I run NGK and more HP than you and have had no problems with them. In fact I've never had this problem with any spark plug, but then again I have never run Denso's either. There really is nothing to chip or break the outside porcelain because on our engines we have a guide, so to speak, to keep the spark plug socket straight and in line when removing and installing spark plugs. They usually break or crack when the socket is not straight on the plug and the inside of the socket contacts either the outside tip of the plug and/or the porcelain.
 

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Discussion Starter #37
I would try another brand of plugs as I mentioned earlier after you figure out what was the cause. Bad fuel, running lean, detonation or a combination of any of those. I run NGK and more HP than you and have had no problems with them. In fact I've never had this problem with any spark plug, but then again I have never run Denso's either. There really is nothing to chip or break the outside porcelain because on our engines we have a guide, so to speak, to keep the spark plug socket straight and in line when removing and installing spark plugs. They usually break or crack when the socket is not straight on the plug and the inside of the socket contacts either the outside tip of the plug and/or the porcelain.
Thanks, yeah I have all NGK in it now. Dave
 

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Whoa thats a lot of damage to that plug. That motor needs to come out before you do any more damage IMO.

FWIW I have been told to never use the Costco fuel in our performance cars. Discount fuel never a good choice for our street machines. I used to think like Goose and anything 93 was good but some much smarter people have told me that not all fuel is created equal. These same people say Chevron/Texaco 93 with Techron is the best fuel for our beasts.
I only run Chevron 91 out here in SoCal. because that's all we have for premium, but I mix it with Sunoco 260 GT Plus to get 93.6 or 94 Octane. I have been mixing my gasoline this way for over 3 and 1/2 years with around 850 BHP and I have nevah had a problem. Funny thing is when I had the stock 47# injectors in it with the same BHP I would occasionally get a lean CEL, but nevah at WOT. I now have ID 1050X injectors and ocassionally get a rich CEL, again nevah at WOT. My plugs have held up fine under both conditions. I know one of these days I should get it retuned to correct this.
 
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Moved this thread to our problems section.
 

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Recently, after a few years of trial and error with spark plug sockets (multiple lengths) and extensions (multiple lengths), swivels, spark plug sockets with captured swivels, black taping sockets to extensions so they do not pull apart in the hole, etc., etc., etc., I FINALLY found a socket that is long enough to get up out of the spark plug hole on the 5.4 DOHC and only use an extension around some of the items like the TB area while also being able to get a torque wrench on the socket without added extensions for most plug location.

The socket shown in the picture below is fully seated in the plug and has a plastic coated magnet to keep the plug in place while lowering into the hole, but also easily releases from the plug when it is time to pull out and the knurling aids while spinning the socket during plug install......



R
 
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