Do The motocraft plugs suck for anyone else?

ChromeDan2000

Registered User
I swapped out to motocraft plugs about 1300 miles ago. They ran, OK at best. I blew the HGs about 1000 mi ago and put a new set of heads on when i did the HGs. I regapped the stock motocraft plugs to .054 and boy was that a mistake. It sputters and dumps under boost. So i pulled the plugs and regapped them to .049 after reading on the forums. Ran alot better. Now I installed a 10% OD and its sputtering and gasping again. Ive checked all my vac lines and my crank case vent and my intake is sinched up. My question is:

What plug do you all run and what gap?

Ive read alot of past posts and it looks like some people run Denso IT20. Anyone else move from Motos to Denso and what did you think of the Denso?

I currently have:
Removed silencer, 10% OD. Removed cats and custom down pipes, Flow master cat back, brand new motocraft plug wires.

I will be installing in the next 100 miles:
80mm MAF, 42# injectors, K&N Cone, ported manifolds.

I am thinking of moving to the Denso's gapped at ~45? Tell me I'm crazy because i REALLY HATE changing plugs on this car.

-DZ
 
I've been using the same set of Denso IT20s gapped to .040 for about 2 years with no problems. Don't put many miles on the car (about 3K per year) so I don't know how long they would last in a daily driver.

David
 
I run the shorter end Autolite double platinum APP764 gapped a little loose at .045 which is the max on the gauge I have. I have borg-warner wires, a stock replacement set which are 8mm.
 
Time for another spark plug post....

1) Platinum is there only for long service life. It does not help give a better spark and is not recommended by any reputable engine builder or tuner for a high performance supercharged application.

2) Iridium is expensive and isn't going to fix other existing problems. The SC has a good ignition system which will not break up or lose spark under any normal conditions. If you have ignition problems, running an expensive spark plug may or may not improve the situation but at best it's only a bandaide.

3) All spark plugs are equally susceptable to antifreeze (sudden death), fouling (not quite so sudden death), and detonation/pre-ignition (more death). Bosch platinum tipped plugs are more susceptable to the above listed faces of death than others and should be avoided at all costs.

4) For stock applications a double platinum plug will provide the longest service interval (about 60-100K miles). In this case the plugs should be replaced with Autolite APP-764's (or equivalent) gapped at no more than .050" and should be accompanied with new replacement Motorcraft plug wires.

The APP-764 is a shorter tipped version of the stock plug. It will run cooler and have less tendancy towards detonation than the stock plug. It is the OE replacement for some late model 3.8's and 4.6's such as the Mustang GT. It is the same heat range as stock but incorporates an improved tip design. It comes pre-gapped at .045" but if you would like to increase the gap slightly you can.

5) For performance applications you should use the Autolite 103 (or equivalent) non-platinum plug. This is a cooler heat range plug which will provide superior performance compared to stock and will last an easy 25k miles without gap erosion. It should be gapped no wider than .040", and .035" is typical for high boost applications (17psi and above or with nitrous). This plug is available in double platinum (APP-103) but again, platinum is not recommended for high performance applications.

The Autolite 103 is an OE replacement plug for the 2003/4 Cobra, all Lightning applications and the new GT. Obviously Ford knows a little something about supercharged motors and it should be noted that the SC is the only supercharged application for which Ford used an extended tip plug. It is my understanding that this was done to reduce idle emissions. It certainly wasn't done for performance reasons.

6) For any car that has been modified and hasn't been tuned or is in the process of any engine buildup or modifications an inexpensive standard copper plug should always be used. If you damage a plug for any reason (such as fouling, for example) your $12 Iridium plugs will become garbage just as quick as a $2 Autolite. Do yourself a favor and use cheap plugs at least until you have eliminated all other possible problems. Additionally, anyone who thinks they have a performance SC MUST get used to the idea that they will be changing or at least removing their plugs at least once a year or 20K miles. If you are not removing your plugs to see how things are going in side the cylinders you are driving with blinders on and just asking for trouble. A performance vehicle should have the plugs removed regularly to check for abnormal combustion. This is an excellent time to simply install new plugs. A brand new Autolite 103 will perform better than any 3 yr old plug. Why do you suppose top racers replace plugs after every race? ;)

7) This is also a good time to talk about plug wires. The OE ignition system was designed for a carbon core, high resistance plug wire. The DIS multi-coil system has plenty of "juice" to fire the stock wires and in fact, some engineers will argue that the OE plug wire resistance is an integral part of the ignition system and reducing wire resistance may have a negative effect on the performance of the system. In any case it has not been shown that any low resistance wire is better than the stock wires in any case. The mindset of "high performance plug wires" comes from a long line of distributor fired engines that relied on one coil to fire 4 cylinders per revolution. Coil saturation and dwell time as well as total coil output were a major concern. In our case with three coils, each firing once per revolution, we do not have an issue with saturation and the coils have plenty of dwell time at any rpm our engines are capable of.

While spark plugs certainly can cause an ignition miss, most often the problem is installer related (cracked procelin, improper gap, incorrect tightness, or contaminants on the electrode) and not related to the plug itself. An exception to this rule is the Bosch platinum plug with the thin platinum electrode. These plugs have been proven to give poor performance on any and all supercharged applications.

Plug wires, on the other hand, cause the majority of all ignition related problems. No plug wire brand is immune from problems and consequently over time it has become my recommendation to use Motorcraft or Taylor wires. They may not be any better than others but they are certainly cheaper so you won't feel so bad if you damage one. In any case the wires should clip on with certainty. If you cannot feel for sure when the metal clip engages the spark plug then you must try again until you feel it. Muscle and force will not make them work better, instead it will damage the ends and you'll end up buying new ones. Never say to yourself "I think I got them on right". Either you do, or you don't, there is no "maybe" unless you don't mind doing the job several times. ;) Also, always use the silicone grease provided with the plugs. Not only will the wires snap on easier but it will be possible to remove them later if needed without tearing the boots.

Other components of the SC ignition system can cause problems as well so don't write them off as sources of your problem. DIS modules are common problems as are cam sensors. Bad grounds (damaged wiring) is also a source of problems but the first and most common place to look is plugs and wires.
 
Last edited:
To XR7Dave.....WOW. That hit the nail on the head....then proceeded to flatten it into the ground with hulk like smashes. I will definitely take all your votes into consideration.

I forgot to mention that when the HGs went, i used the same plugs because they still looked clean (i had a slow seep leak). When I pulled the plugs last week they were not fowled in any way, looked very clean so I assume I'm not fowling them out. The car also has a new ignition box. I might ohm out the coil to make sure its not getting weak. If it is hosed, has anyone tried the screamin' daemon pack that SCP sells?

I will keep tweaking with it, that is, until I loose my mind changing plus on this car.

-dz
 
2) Iridium is expensive and isn't going to fix other existing problems. The SC has a good ignition system which will not break up or lose spark under any normal conditions. If you have ignition problems, running an expensive spark plug may or may not improve the situation but at best it's only a bandaide.

The Denso IT 20's are slightly colder then stock. I noticed that when I was running ungodly boost #'s the iridiums at the factory preset gap took care of my top end sputtering problem.

There can be other issues you are facing however if you said lowering the gap helped...Then when you raised the boost you had issues again..The iridiums may just help you out..Sounds like your blowing the sparkout

May want to invets in new o2's being ya blew yer gaskets as well
 
Well, I was pulling the plugs again, scrutinizing the hell out of them this time. I found a long hairline crack running down the side of the porcelain stem to stern. So maybe i gave Motos a bad rap for something I probably cracked while putting the engine back together. I will probably get a few extra Motos to replace the cracked ones but I think I will start the search for a different plug after reading all your input.

Thanks.

_DZ
 
Time for another spark plug post....

*snip*

Perfect timing. I was going to make another spark plug/wire post as the search function wasn't helping. Unfortunately from your post it would appear that user error is a fault. I hate user error.
 
I ended up installing Autolite 103s gapped at 0.035 and it runs beautifully. This is a weekend cruiser so even with the short service interval they will last plenty long. And at 6 plugs costing as much as just one motocraft...I'm very pleased.

PS. Anyone else agonizing through the plugs (which I have gotten very fast at as of late) should pick up one of these.

A Craftsman 3/8 in. Drive Ratchet, Flex Head
http://www.sears.com/sr/javasr/prod...tical=TOOL&subcat=Ratchets&BV_UseBVCookie=Yes

It makes plug changing a breeze.

-DZ
 
You can also use the Motorcraft equivalent to the Autolite 103, which is AGSF 22 C. These are inexpensive as well. We used them in my 95, gapped at around .040", and it's running 19.5 psi now ... no misfire. :)


cheers
Ed N.
 
Back
Top