Why Yes another sparkplug thread...

91 XR7

Registered User
I read through here.. and know the suggested plugs to use.. BUT i am also only after just normal OE replacements..

I called up my local Parts store i deal with (Napa) and asked for some Replacement spark plugs for my '91 SC.. What i got was NGK G-power (TR55-1GP / 7159) plugs.. I only found one thread dated back in mid 2005 to stay away from these? (well G-powers)

Should i request something else??
 
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You would want Autolite 2544 for copper or APP2544 for double platinum (don't bother with the AP2544 single platinums). These used to be called 104s, but they changed the part numbers. You can go colder with the Autolite 103s, but that part number may also have been updated. I forget.
 
Stock replacement will be an autolite or you can get a motorcraft plug from Ford which is the same as the autolite. Should be an Autolite double platinum plug for the SC.
 
Well it was looked up, even when i was there, in their book and it said they where for this car.. so..

But yeah, went back today, she wasn't there thou, Ordered the 2544's (was suppose to be in in an hour, but i had other places to be)
So i'll be trading them tomorrow
 
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Well i just finished Pulling the ORGINAL Spark plug Wires, and i swear sparkplugs too which brings me to some Questions :)

All 3 on the passenger side, the Ground Electrode Was nearly gone, and the the drivers side just seemed like typical 100,000mile worn out.. is this Normal?? And could be be the same kinda reason why Ford orginal with the 4.6L had two different plugs in them, One P/N for the passenger, another for the drivers??

Also would it be wise to swap the Leads at the Coil packs to help `even' out the wear after say 40-50,000 miles?? :p

Also the hardest part of this job has been the spark plug leads themselves OFF! The plugs where easy to come out, not much room to swing the ratchet, but still `easy' :) Now to put it allback together (IE install new plugs and wires)
 
The plugs where easy to come out, not much room to swing the ratchet, but still `easy' :) Now to put it allback together (IE install new plugs and wires)

what do you call easy? I'm getting ready to change mine and they look like a complete PITA :confused:
 
what do you call easy? I'm getting ready to change mine and they look like a complete PITA :confused:

Like i said the Hardest was trying to get the Spark plug leads themselves off the plugs (even back on :rolleyes: ) I forget which `spark plug' thread.. But someone posted a link to a `how to' and i basically followed it for the removing the plugs themselves..

Also i found, least on my '91 SC, that the #1 plug can get gotten from under the car too But from the front of the Cross member.. You semi do have to feel your way but it's still not that hard...

Oil changes = Easy (YES even on a SC AND 4.6L :eek:, 5.0L is a breeze too )
Tune ups = Easy-ish even thou on my SC it DID take @ 2hours on a hoist (not bad for the 1st time)
Heater Cores = Easy
5spd swap = Easy

I originally bought my '89 XR7 for a `parts car' But 1: it was to good of a condition 2: I wanted a challenge 3:Cheap too
I Bought the '91 SC for 1: It was cheap 2: In Good condition (For the lack of `love' the previous owner gave it.) 3: 5 spd 4: 100,000miles 5: it was Cheap :)



Changing Plugs and Wires
There yah go.. Like i said in the blue above.. #1 can get accessed from below and with out removing anything.. unless your doing wires, then just the Rubber intake tube needs to be removed for little more ease in THAT department..

All and all It may look intimidating abit, But it's not all that bad.. Don't know what it's like on say JACKSTANDS thou :p
 
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Sounds like the plugs were way to old and likely not even the double platinum plugs. Perhaps single platinum if the ground electrode was worn more than the main.

Stock plugs should be good for 100k miles without significant deterioration if the engine is running well.
 
I'm pretty sure they where original plugs, Just because of the wear.. and I forget the number.. 34PP comes to mind? :confused:

the Leads had `1991' on them, so i KNOW they were original..

Even thou the idle has smoothed out some it still has a roughish idle thou (kinda like it has a mild cam in it) So i'm sensing their is more to be done..

Just to give you what i've been up against with this car, and lack of true Maintenance, other then when a part on the car fails completely :rolleyes:

Picture%20010.jpg

This is from Holding both ends of the fuel filter with some fuel still in it, and shaking it and pouring out (from the inlet side) the contents..

Picture%20011.jpg

Filter Cut open.. Nice collapsing Filter pleats, and you can't see it, but theirs a LAYER of dirt on it that you can seriously scrap off (it's like a 64th of a inch or something, but still)

Makes you wonder about the fuel pump and pick up sock... :eek::eek::eek::eek:


If this car could talk.. it'll be saying `thank you for saving me'
:eek:
 
Agreed, the hardest part of a plug job is usually getting the stupid boots off the plugs! It might be nice if Ford would use some grease or something ...

By the way, this type of ignition system makes the spark jump one way on the driver's bank and the opposite on the passenger's bank. So, one electrode wears more than the other on each bank. I am not sure about the plugs on the SC, but I know that on the later Windstars with DIS ignitions, Ford realized that it could save a little money by only putting platinum on the electrode that saw the most wear. So, there is a different plug for each bank - one has the platinum on the center electrode, and one has it on the ground electrode. The reason you should go with double platinum when you replace them is that you don't want to get it mixed up. Besides, the aftermarket single platinums only come in one variety (they have the platinum on the center electrode, I think), so you would have to get 3 double platinums anyway to get any platinum on the opposite electrode.
 
...
By the way, this type of ignition system makes the spark jump one way on the driver's bank and the opposite on the passenger's bank. So, one electrode wears more than the other on each bank. I am not sure about the plugs on the SC, but I know that on the later Windstars with DIS ignitions,
...

SC is waste spark. Two cylinders fire for each spark event. For the plug that is in the cylinder on the compression stroke, the plug fires from center electrode to ground. The other cylinder fires from ground to center electrode. If flips back and forth like that based on which cylinder is on the compression stroke.

Thus the need for double platinum plugs. Both electrodes get a work out.
 
SC is waste spark. Two cylinders fire for each spark event. For the plug that is in the cylinder on the compression stroke, the plug fires from center electrode to ground. The other cylinder fires from ground to center electrode. If flips back and forth like that based on which cylinder is on the compression stroke.

But why would the plugs on the passenger side be worn differently then the ones on the drivers side?? If going by your theory that the spark travels in both direction Dependant on which combustion chamber has the least amount of resistance?? So in theory they should be worn the same..
 
Mike8675309> SC is waste spark. Two cylinders fire for each spark event. For the plug that is in the cylinder on the compression stroke, the plug fires from center electrode to ground. The other cylinder fires from ground to center electrode.

For those that wonder why...

"...the electrons will align themselves favorably with one direction of current flow. While the one plug will receive positive potential (voltage) at the wire side, the piston pair will receive the negative potential. The negative potential is what causes the second plug to fire instead of the voltage just going straight to ground after firing the first one. Vehicles seem to use the conventional theory as opposed to the electron theory of current flow. Even though the spark plugs are manufactured exactly the same, if they are re-installed after there has been some extended use, they should then go back into the cylinder from which they came from."

Which cylinder did you say that used plug came out of that was yanked at the junk yard? :)
 
So the Windstar is not waste spark? Why is Ford using two different single-platinums on those?
 
Ford used single platinum plugs on all DIS motors. Replacements from Ford are all double plat, but the original installation were single plats with opposite plat contacts for each side of the motor. You can't buy them this way, that was something for the assembly line only.

If someone reversed the plug wires then they would fire backwards and wear out pre-maturely. Either that or the plugs might be on the wrong side of the motor on accident. Also, if someone previously replaced the plugs with single plats then that would also explain why one side would have worn electrodes.
 
i was 100% sure the plugs in my '96 (4.6) where original, they were 2 different part numbers for Left and right... Double platinums (Ford) went in on that car..
The '91 SC i'm not 100% sure if they are original.. But being how they seemed pretty worn out, i would expect they are.. Never did look at the part numbers on them thou... I still have them, so i can figure it out... But Double platinums went in... But the ones that came out, the ground electrode was near gone on the passenger side, but in decent shape on the drivers (which was still worn thou)
I know the ones in my '89 XR7 weren't Originals.. (have receipts for least 2 `tune ups' including wires, plugs, Fuel filter, Air filter, oil and filter, ect)

So if one did have double platinums in their car, could swaping spark plug leads at the coil pack be a good thing or bad things?? (Performance wise it'll won't do anything)
 
Ford used single platinum plugs on all DIS motors. Replacements from Ford are all double plat, but the original installation were single plats with opposite plat contacts for each side of the motor. You can't buy them this way, that was something for the assembly line only.

If someone reversed the plug wires then they would fire backwards and wear out pre-maturely. Either that or the plugs might be on the wrong side of the motor on accident. Also, if someone previously replaced the plugs with single plats then that would also explain why one side would have worn electrodes.

I agree. But Mike and KMT are saying that the direction of spark reverses based on what stroke the cylinder is on. To me, that doesn't jive with what Ford did in having two different plugs. I think the compression spark would be higher-energy than the waste spark (because denser air makes greater resistance in the air gap), so that spark should have higher ability to erode the electrodes. If the spark in the compressing cylinder always jumps the same direction (center to ground), then shouldn't both banks have platinum on the same electrode? But they don't ...
 
I agree. But Mike and KMT are saying that the direction of spark reverses based on what stroke the cylinder is on. To me, that doesn't jive with what Ford did in having two different plugs. I think the compression spark would be higher-energy than the waste spark (because denser air makes greater resistance in the air gap), so that spark should have higher ability to erode the electrodes. If the spark in the compressing cylinder always jumps the same direction (center to ground), then shouldn't both banks have platinum on the same electrode? But they don't ...

You aren't following the path of the electricity. One coil fires both banks simultaneously, one on compression, one on exhaust. Both are fired at the same time and the current only flows in one direction. There is no distinguishing between the waste spark and the power spark, the only difference is that one plug fires under no pressure (low resistance) and one fires under high pressure (high resistance). The ignition system doesn't determine which plug fires the mixture, that is purely a function of the resistance of the plug gap.

Therefore one bank fires in "+" and one fires in "-". You can reverse this by switching the sides of the coil that your plug wires attach to.
 
S_Mazza> But Mike and KMT are saying that the direction of spark reverses based on what stroke the cylinder is on

It doesn't 'reverse' (toggle) - both plugs fire in a loop, which means that one cylinder is fired in reverse polarity of the other.
 
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