Hello,
Someone posted the required spark plugs for the 4.0 engine, I recall there are 3 spark plug numbers for the passenger side, and a different number for the driver side.

I cannot find this posting. Can anyone help?
Thanks.

 

You aren't going to go searching for these separate spark plugs and put two (or three?) different numbers in your Aerostar, are you?
From the factory, Ford sometimes used different plugs in the same engine because half of the cylinders "pushed" the plug voltage and the other half "sucked" the plug voltage. (that description is not correct, but it's the best way to describe it) They put the precious metals either on the electrode or the ground, depending on what cylinder the plug went into. The precious metals were put there to slow the increasing plug gap as wear naturally occurs. Just buy a good double platinum spark plug to go into your Aerostar and sleep well at night. And hopefully all the scratches on your arms heal quickly.

 

Kruse,
the 4.0 developed a missfire overnight.

I replaced two plugs with Irridium plugs but it continues, Then after about 25-30 minutes of driving in what it feels like it's running on 5 cylinders, the missfire dissapears and the engine runs on 6 cylinders again as if nothing had happened.

I have 4 more plugs to replace, yes I will get the old scratches re-scratched !

are Irridium plugs ok on both sides ?
Thanks.
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To be honest with you, I've never used an irridium spark plug...on anything. I was always a platinum or double platinum guy. I don't see why irridium wouldn't work. Let us know how they perform.
On a side note, one of my Aerostars developed the same symptoms as what you describe. My wife and kids were 500 miles away and they took it to a Ford dealership. I talked to the tech on the phone and he assured me that a new plug would cure it, but it had to sit overnight. He wasn't going to touch the thing while it was hot. A new plug cured it. The misfiring plug wasn't that old and the other five plugs lived a good, long life.

 

Thanks, my experience with the 1997 4.0 has been that it eats spark plugs like crazy.

I just went and purchased more NGK Irridium to replace all spark plugs. I am waiting for engine to be cold.

 

My experience with the 1997 4.0L has been the exact opposite as yours Jose A., I never have any spark plug issues, they seem to last forever, 'knock on wood'

First lets start with a little brief history refresher of the 4.0L ignition system:

I believe that the different spark numbers you mentioned might have been the original Motorcraft AWSF-42PG and AWSF-42P installed in the Aerostar.
(Repair Manual CD, Group 03: ENGINE, Section 03-07C: Ignition, Electronic -- 4.0L.)

Cylinders #1, #2 and #3 have the PG suffix.
Cylinders #4, #5 and #6 have the P suffix.

PG suffix = Ground (side) electrode is enhanced with platinum.
P suffix = Center electrode is enhanced with platinum.

Ford's use of two different spark plugs was done because the 4.0L OHV utilizes a waste spark system, one coil fires two plugs simultaneously, so these plugs fire twice on each completed full cycle, the spark plugs fire once on the combustion stoke and then fire again on the exhaust stroke, thus the term 'waste spark' or it is also commonly referred to as 'reverse fire'. So due to this 'reverse fire' the spark plugs in cylinders #1, #2 and #3 will put more wear on the ground electrode, where as the 'normal fire' spark plugs for cylinders #4, #5 and #6 will put more wear on the center electrode and thus the need for Double Platinum enhancement on both electrodes. See the illustration that I created below for a visual of the waste spark system.




I believe Ford used these two different spark plugs as a cost savings measure in 1997 due to the high expense of double platinum plugs back then, but today, it is not as much of a cost issue as it was back in 1997.

The Motorcraft AWSF-42PG and AWSF-42P were then later made obsolete and superseded by the Double Platinum AWSF-42PP, maybe this is the third plug you mentioned.

PP = Double platinum enhancement on both the ground (side) and center electrode.

So, fast forward to today, it now depends on which NGK iridium spark plugs you are buying, as you did not mention it.
The NGK Iridium IX has an iridium center electrode only, with a standard nickel ground electrode, so cylinders #1, #2 and #3 will wear out the ground electrode prematurely, and only cylinders #4, #5 and #6 will use the advantage of the denser iridium center electrode, so I would pass on this spark plug because it really is no better than, and will not last any longer than any good old standard copper/nickel plug for the Aerostar with the waste spark ignition system. Any standard Double Platinum will last much longer for this engine than the NGK Iridium IX.

Next is the NGK Laser Iridium which has an iridium center electrode and a platinum disc welded to the inside of the ground electrode, this would be the preferred one to use, since you seem to be using the NGK brand now, as both electrodes are receiving an enhancement from iridium and platinum on them, which is what a waste spark system needs for longevity. That said, I have no personal experience with NGK plugs on the Aerostar but they seem to be of very good quality. That all said, there is no advantage to Iridium spark plugs in the Aerostar when the Iridium tip is on only one electrode, these spark plugs are only as good as their weakest link, the Iridium is great for longevity but it is paired with a platinum ground electrode, which is the weak link here, so thus I would just get a Double Platinum like the NGK Laser Platinum for $6.93ea vs the NGK Laser Iridium at $9.19ea, RA.

So the question still remains as to why does your Aerostar "eats spark plugs like crazy"?
I do not know exactly why, but I think two areas you might want to explore are, either you are (1) running too cold of a heat range plug or (2) possibly the wrong type of spark plug.

Since we do not know which NGK you are using, I can tell you that the NGK Iridium IX that I listed above is a waste of money and probably if I were to guess, would last only 10-20k miles tops. Now remember, going 10-20k miles on a set of plugs in a waste spark system is like going double the miles, 20-40k miles in a regular ignition system since the spark plugs fire twice as often and have twice the wear.

Ford also issued a TSB quite awhile back (decades ago) on increasing the heat range on the Aerostar from APP103 to APP105 because of a misfiring problem due to the plugs fouling out, so Ford's increase in the heat range seemed to fix the fouling out problem.

I am curious, what is the mileage you normally get on a set of spark plugs, every 10k, 20k, 50k, just how 'hungry' for plugs is your Aerostar?

 

in my experience its easier to change some of the plugs through the wheel well.

 

Front_Range_Aerostar

NGK TR551X are the plugs I am going to install

Thank you for the informative writeup you posted.

 

Your are welcome Jose A. and I hope the new plugs fix your problem.

I will just reiterate what I said above, the NGK TR55IX only has iridium on the center electrode and just a standard nickel ground electrode. The center electrode iridium enhancement is of no benefit in cylinders 1,2 & 3, as these are the "Reverse fire" cylinders where the ground electrode needs the enhancement, so these NGK iridium plugs are no better than, and will only last as long as a standard nickel spark plug.

The NGK TR55IX will not last as long as the original OEM plugs that your Aerostar came with from the factory, even NGK acknowledges this on their website, NGK has only one spark plug that meets the original OEM design specifications for the Aerostar, and that is the NGK Laser Platinum.






This is why the spark plugs in your Aerostar do not seem to last very long.

 

I just happened to have 4 of those NGK plugs handy. I am not a fan of NGK, I actually prefer Autolite.

Anyway I completed installing 5 of those plugs and now I am fighting with the worst one, the rear one at the driver side.

I have read some people drilled a large round hole to have access but I don't have the tool.

There is just no room for a long 5/8" socket and a wrench. Will keep trying.

Thanks for the tips, next time I will fit the proper plugs you suggest, right now I am trying to cure the missing , it must be that last plug.

 

Hello,
that last spark plug was a mother. I made it but man.

Still.missing. But a lot less. The hesitation is mostly gone. I get the feeling I have a bad valve. Could have gotten damaged for red light racing with BMWs and others. The Aerostar leaves them in the dust.

My nephew ( master Honda mechanic at Darryl Waltrip's Honda dealership in Franklin TN ) says it's Vacuum.

I checked every hose and tubing, Only thing is to do the smoke test.

Even as it is, it has lots of power, and the bad missing it gone, It was the last spark plug, an Autolite !

 

I always used the dp ford plugs. 100k

 

my 4.0 broke an intake valve spring on the front battery side.major vacuum leak.it barely ran.i drove it like that until it wouldn't pass inspection because of no power brakes.it was a pain getting the valve cover off to change it.the lifter flew apart so i removed both pushrods and unplugged the fuel injector.

 

I drove without the doghouse cover to listen to the engine. It now seems normal, the misfiring is gone after replacing spark plug number 6, which by the way, came out in pieces, the ceramic insulation was cracked and missing a large chunk. I am satisfied the misfire was not a valve but the one spark plug. It now has 6 new spark plugs and roaring like a dragon on acceleration.

I have to stop leaving Bimmers in the dust.

Again, thanks to Front_Range_Aerostar for the help.