Going to change the plugs in my 94 4.0 A4WD and was wondering if anyone would suggest a type of plug? How about the splitfires or the Bosch 4 prong platinum?

 

How did you manage to pick two of the worst plugs to use? Stay with Motocraft platinums!!

 

you have a 4L with the EDIS ignition system which requires double platinum plugs, center electrode and ground tipped with platinum for long life and erosion wear prevention...

Autolite, manuf's of Motorcraft brand also, are the only ones making the correct heat range double platinum plug for the 4L V6 Aero engine....either brand in double platinum will last 100,000 trouble free miles.... other brands will have short life, increased wear, preignition which is damaging to the 4L and loss of engine power....
as difficult as it is to change 4L plugs....do it once

 

In some cases, Motorcraft has replaced the double platinum plugs with "fine wire" platinums. This is the case with AGSF12PP, they have been replaced with AGSF12FMF6.

 

So what would be the part number for a '93 4.0?

 

From Motorcraft's website, the correct plug P/N is: AGSF42FM

 

I used Motorcraft, Bosh and NGK. I can see no differense!

 

Pablo,
this is for the EDIS 4L V6, they are very particular on plugs...these engines are suseptible to too hot plug heat range preignition and electrode erosion wear....stochiometric ratio air/fuel mix engine operation requires almost perfect spark plug heat range design....

older distributor engines will run just about anything for plugs....used to use old farm tractor plugs in an old Ford flathead V8 PU i had, too cheap to buy new...dad would change plugs in tractors in spring....i would scavenge the old plugs out of garbage and put in PU....ran fine...price was right

i agree with you that the new Bosch 2 and 4 ground plugs work outstanding in other apps, Honda MC VTEC I4's and V6's really perform with them....no spark shrouding...spark completely exposed to fuel/air charge...i have seen no gap change after 50k miles

 

I put bosch platnum plugs in my 3.0 89 aero at 168k, i'm at 210k now and still going strong.

 

MOTORCRAFT -or- Autolite Only!!!!! Bosch Plat. and others will fire in the cylinder. However, I guarantee, you are not getting the correct, full spark and combustion cycle with this plug. Surf around the internet, and you will find this, when certain Ford motors are run on a dyno. Ford carb engines, can get around with various plug types. However, fuel injected, emission controlled Ford engines, are built and designed with a certain plug in mind. Namely the above mentioned, Motorcraft and Autolite, which is essentially the same product.

 

I changed the plugs in my 4l at about 110kmiles. They were very obviously worn, but I did not notice any improvements in performance or mileage, or ease of starting. But as the plugs wear out, their gaps widen, and this is where you really need good wires. The wider gaps will present higher resistance to the spark, and worn insulation will more likely allow sparks to form between the wire and other metal parts because that path will have less resistance.

Boy, you can say that again! Back in 1979, I worked on Ford's ProCo engine, a highly modified 302 v8 using a prototype of the EEV-IV for engine control that took up the whole front passenger seat (and footwell). It was Ford's attempt at making a stratified charge engine, like the Honda CVCC. It had 2 plugs per cylinder; one in the normal place, but the other went in from the top of the experimental head. That second plug was custom made, probably in-house, and had 1" long electrodes. The engineers who designed that set up talked about things like specially shaped combustion chambers, putting the spark into the high vortex stream of air and fuel mixture, and timing it relative to the first plug. It was all quite complicated, and I have forgotten most of it, but I do remember that the location of that second set of electordes was very important.

That was a purely R&D project from which much were learned and later applied to cars that eventually hit the streets. But somehow, most of today's newest street cars still seem really conventional in comparison.

 

Your on the right track. What happens, a wider gap requires a higher voltage to create a spark. Over time this higher voltage will break down the insulation on the plug wires, causing the wires to arc to ground, instead of firing the plug.

 

One thing you will also find, is the heat range of the plugs from different manufacturers will vary, even though the gap and length are the same. So the Bosch plug may have the same gap, and pull up in the parts stores computer as a cross, and the fact that it is platinum will make some people think it is superior, and in some applications it may be. But in an Aerostar, these plugs will cause problems with proper ignition. They randomly miss, the build up carbon deposits, they overwork the wires, and they wear down quickly.

 

Gentlemen,
It's hard to argue with success. My Bosch platinums are nearing 85,000 miles of trouble free service in our 4.0.

 

AC,
you have convinced me, which Bosch's, singles 2 or 4's???
plug number for correct heat range?
what else you running Bosch in?

my 4L gets Bosch next time, they will probably last longer than van!

wife's HMC VTEC DOHC 4 and V6's just scream past redline with the Bosch 2's and the gap never changes, no wear at all....no missing...perfect cold weather starts....no plug failures