Q: What spark plugs are the best for my engine?
A: Motorcraft AGSF32PP or AGSF32PPM (formerly AWSF32FS) Double Platinum spark plugs or the equivalent Autolite APP104 (APP764 is discontinued but will work) Double Platinums. Due to our cars' DIS, both anode and cathode need to be platinum or platinum plated. To reduce emissions (especially when cold) our spark plugs fire in pairs (one cylinder on the compression stroke and one on the exhaust stroke) to re-burn any remaining unburnt air/fuel mixture. Therefore, while one plug is firing anode to cathode, the other is firing cathode to anode. Use of non-double platinum plugs will greatly reduce the life of the plug and may lead to drivability issues and misfires.
After another plug coming loose on me I decided to get a new plug and locktite it in there for good before it strips out these threads like it did before(I know this sounds like a terrible idea but I don't plan on keeping the engine for long anyway). So I picked up a APP104 and when I compared it to the APP764 that I took out, I realized the latter have about half as many threads then the new plugs.
So everyone check and make sure you are not using Autolite APP764's. This may be the reason why many of us our having problems.
I have a hard time believing this. I will check when I get home but I am more then possitive I have always used APP764 and have some in my car at the moment. I have never had an issue with plugs coming loose or blowing out of the head.
are you sure you installed them correctly? alittle anti-seise and alittle more then hand tight on a bone cold engine?
the only thing the amount of thread would change is how deep into the head the spark plug sits.
I use a tiny amount of anti-seize and torque them to spec. If there are less threads then you would need to tighten them less and they would be more likely to come out or... you would tighten them by the same amount and each thread would be under more stress increasing the likely hood that they fail.
That is what I'm saying. The plugs have about half as many threads and therefore half the threaded area as the others.
But just because that plug has half the threaded area of the other plug means nothing without knowing how that plug's threaded area compares to the threaded area in the head. Do you know that comparison?
I don't think the extra threads on the other plugs are engaging anything.
I have a head off a 2.5L that i could count the number of threads. as long as the plug itself has the same number or more threads than it doesnt make a difference.
FWIW, it seams only NECO has problems with plugs backing out of the head. lots of people use the APP764 over on CEG without issue, I know i used them for over a year without problems.
edit: the head has about 8-9 threads. this head also had the motorcraft iridium plugs that have the short section of threads. there are about 6-7 threads on the plug. that means you will have about 1-2 threads less engagement, however you only need about 6 threads on a steel to aluminum threading to get enough torque to not have problems.
Last edited by Turbo Zetec Tour; 2010-09-02 at 08:44 AM.
Daniel - TZT Performance '93 Mitsu 3000GT VR4 - 230K miles and counting
2000 Black SVTC #391 - sold '97 Contour GL Tutrbo - sent to the crusher Jan 09
I've used both for years in many engines without any issues. I'm not sure why anyone would have a plug back out. Torque it correctly and you shouldn't have any issues. BTW you can't really buy APP764 anyway unless a store had an overstock and are still trying to get rid of them. They were discontinued and have been for quite some time. APP104's are the replacement. Are you sure you had the right plug to begin with (APP764)? Did it actually say that on the plug? Do you have stock motor? I'm running boost with APP764 plugs and they've been great. Higher pressures will greatly increase the chance of a plug backing out. Mine are good and I check them often.
I ran a search online and it sounds like the APP764's ARE stock size. The APP104's are longer than stock only by about 2.51mm or .1" so those with APP764 plugs will be fine. From what I can tell that plug is used in a lot of Fords and the F150 was having plugs blow out so they came out with the APP104 with a few more threads. Replacing plugs in the older F150's was horrible so I'm sure that was a huge deal.
Side note: Remember to verify they are APP (double platinum) and not AP (single platinum). I've seen it happen quite a few times where the guy behind the counter gets an AP plug instead of the APP. Usually it's when I send someone on a parts run that isn't paying attention...