[cgrey8]

I installed some Autolite copper plugs into the engine a few years ago for diagnostic purposes thinking one of the plugs I had in there might have been bad causing some horrible intermittent misfires. The problem turned out to be something else, so I left the cheapos in the engine anyway just out of laziness not wanting to swap them back since they were working just as well as the ones I pulled.

Well today, a few years later, the cheap Autolites are starting to give me trouble. I'm getting intermittent misfires & partial fires at cruising conditions as well as sluggish and unstable cold takeoff...even with the MSD ignition box. My guess is without that box, they would be performing far worse. Or perhaps because of the ignition box, they are going bad prematurely??? I don't know. Regardless, I'm fairly sure they need to be replaced. After all, they are Autolites and the cheapest plug AutoZone sold for a 97 Explorer 5.0L.

Since I'm replacing them, one of the things I would like to do is replace them with colder plugs since it's a high compression engine. With a 160 degree T-stat and some spark retard, I can actually run 87 octane on the engine, but just barely. I'm thinking a cooler plug would work better particularly as the spring and summer months start returning.

So earlier this week, I went to AutoZone to get some Champion PN 13 (aka RS14YC6) plugs with a heat range of 14, which at the time, I thought made them a cold plug. But looking at the plug, the construction looks far more like a hot plug than a cold plug. Getting suspicious of this, I decided to do some research and sure enough a Champion 14 appears to indicate hot, not cold according to some heat range charts I found on the Internets showing a number of different plug mfgs and their numbers.


So I'm taking them back.

Doing some further Google searching, I found a similar thread from about 2003 on a different forum:
DFW Stangs>Colder Plugs with GT40Ps (supercharged)

From that thread, the guy there is recommending:
Motorcraft AWSF-22C
NGK 4177

The one thing I did learn from that post is that mfgs assign heat ranges differently. Some lower numbers are hotter and others lower numbers are colder. As you can also see from the chart above, there's no consistency thus you shouldn't attempt to compare plug heat range values from different mfgs. This makes AutoZone's declaration of heat range kind of useless and actually misleading when you use the compare feature on their website. Add to this, the Autozone desk guy (a store mgr) didn't seem confident in what the number was either but that didn't stop him from telling me he believed those Champions to be cold despite my pointing out the construction of the insulator being deep...what I'd expect from a hot plug. He just shrugged his shoulders and was like, are you gonna buy them or not?

[Paulie]

I don't know about Champion or NGK but for Autolite and Motorcraft, the lower the number, the colder the plug. The stock Motorcraft plug for a 97 5.0L Explorer would be an AWSF32 and one step colder would be an AWSF22.

[decipha]

NEVER use champion plugs on anything not even a lawnmower

toss a set of autolite 103s in it and be done

[cgrey8]

Thanks to all the responses. I got a set of Autolite 103s. Hopefully they'll be in by the weekend.

[cgrey8]

I got the plugs installed and I found some issues that were likely the real cause of the intermittent missing.

First of all, the plugs all came out looking pretty decent. No major or obvious issues and all looked pretty consistent in appearance. The insulator on all of them were rather dark gray, not brown. But they were not glazed, caked, or charred looking. I'm not 100% sure what that means, but I'm throwing it out there so if someone does know what that's a tell-tale sign of, they can enlighten me (and the other readers that stumble across this post).

The main problem was the #6 plug wire that's been draped right across the steering shaft. The boot is straight and is about an inch from the shaft, so the wire runs right over the top of the shaft. The rotation of the shaft wore a notch in the wire which was getting deep enough it might have been intermittently arching to the steering shaft instead of arching across the plug's electrodes. Although the notch was not down to the inner sheath or core. I fixed that by zip-tieing the wire up a bit and covering the notch with electrical tape so if it does work its way back down onto the shaft, it'll have to wear through a fairly thick wrap of electrical tape. If that doesn't work or causes problems in the future, I've got enough old wires I can replace that 1 with. I think I have a wire that has a 45 degree boot, but it's from a 9mm blue wire kit. The wires on the engine now are 8mm black.

The next problem was some moderate corrosion on the tip of one of the plugs. I doubt it was actually causing any issues. Even with the corrosion, I'm fairly sure the sheer closeness of the plug tip and wire connector were such that the voltage could easily make the jump. To combat that, I put anti-seize on the tips of the plugs so the wires hopefully don't allow corrosion on the new plugs.

The other problem I noticed is I never gapped the plugs that were in there, which were Autolite 768. The Autolite 103s were gapped to ~0.50". And that stands to reason given the 768s came out at roughly ~.55". I gapped the 103s down to ~.35". I generally like the idea of a wider gap. But I decided I'd see how a smaller gap works.

So far so good with the 103s, but it's way too early to make any kind of judgement on whether the colder plugs are actually doing anything better or worse. I'll give them a thousand miles or so and pull one to make sure they aren't caking or fouling. If they are, then I'll know despite the high compression and MFA lean burn, the colder plug just isn't working. But my gut feeling is a high compression can benefit from a colder-than-OEM plug particularly given the stock Explorer 302 is a rather LOW compression engine.

The intermittent missing is gone and loaded idle is noticeably smoother (i.e 1st gear, closed throttle, clutch all the way out). Prior to the plug change, I could feel the imbalance in cylinder power production causing the truck to jump or surge. It still does that a little, but not nearly like it did, and always has since I got the 331 installed...but the surging had gotten worse with the 768s.

The cranking stumble is still there, so that's something else. I just need to take the time to figure that out and determine if cranking is too rich, too lean, or if I'm just dropping the ISC closed a little too far at lower ECT cranking conditions. That's a relatively easy fix. I was just hoping it had something to do with the plugs.

[89mustangnotch]

Any update on how the .35 gapped held up I'm thinking of switching to 103s for my 10psi boosted gt40p setup. I was reading something about xp103s how they have a better kernel flame and take less energy to spark. Which sounds a lot better. Anyone have any input on these news xp103 autolite plugs

[decipha]

ive never run the x's

I use the autolite double platinums exclusively and never found a reason to use anything else

let us know how it works out

[cgrey8]

Any update on how the .35 gapped held up I'm thinking of switching to 103s for my 10psi boosted gt40p setup. I was reading something about xp103s how they have a better kernel flame and take less energy to spark. Which sounds a lot better. Anyone have any input on these news xp103 autolite plugs

They are still in the truck and doing well. Although I could probably go back to normal plugs now that I've transitioned back to a 180 degree Tstat. When my 2nd or 3rd 160 died, I said to heck with this and put a 180 in. I never had issues like that with any of the 180s or 195s I ever used in the past. So I've been running with a 180 which did force me back to premium. The 87 octane just couldn't tolerate the high compression AND higher engine temp without pinging. And the cooler plug was intended to further aide 87 octane in working in a 10:1 engine. The Tstat had far greater affect on whether I got ping than I can say the colder plugs did. To be honest, I can't say whether they did anything or not. They certainly didn't make anything worse so I've had no motivation to swap them.

...I use the autolite double platinums exclusively and never found a reason to use anything else...

I thought you ran old school coppers? Also wasn't there some issue people were talking about with Platinums and boosted engines hence the migration of the industry to Iridum?

BTW, the only purpose (that I'm aware of) for the double platinums was to be an easy replacement for people with coil pack EDIS. From the factory, coil pack engines usually had 2 different spark plugs installed (different part numbers). One set had the platinum disc on the electrode. The other had it on the hook. That was because coil packs send power into a plug, then to the block, then from the block (i.e. hook) into the electrode of the corresponding plug, then back to the coil pack. Thus one plug always gets electricity flowing in the "opposite" direction hence why the platinum disc was on the hook. The double-platinums just put a disc on both electrode and hook so it was dummy-proof. But from my understanding, there was no need for them on distributor-based engines OR COPs. And for those that aren't aware, the direction of current flow does matter when it comes to which end of the spark does more "damage."

[decipha]

nope I use the APP which is the double platinum series, I don't think I've ever use any of their copper stuff

I have a full list of plugs I recommend in my pre tune info

[cgrey8]

Old thread followup.

For the past few months, I started noticing that the engine was having a harder time cranking sometimes and wasn't idling, light throttle running, and accelerating as smoothly. And when I say accelerate, I mean typical 1st & 2nd gear take offs, not tire-screeching WOTs. It was really starting to get annoying particularly the "floating" light throttle where the engine couldn't decide if it wanted to run faster or slower than the truck, the result being the engine chattering the gears in the trans & rearend back-n-forth. But it never acted like a misfire...just not smooth. I even tried reducing the spark advance at light-to-mid throttle conditions at the low RPMs where this happened. That actually helped for a few months, but then degraded right back to where it was.

The datalogs didn't reveal anything telling with the fuel mix. So I thought I'd start with the simple stuff...like the cheap Autolite 103 copper plugs I installed back in 2017. I kept the Autolite Platinum plugs (AP764) they replaced since they seemed to be in excellent shape when I removed them. And add to that, the colder 103s were just an experiment to see if they would burn lower octane fuel any easier. And as it turns out, they never really made any difference I could tell at all. And because of that, there was no reason for me to bother pulling them back out.

But now, I had a reason to think maybe they were the cause OR at the very least, pulling them might be able to tell me something about the condition of the engine that might explain the rougher engine running condition I was experiencing. So this weekend they got pulled. And looking at them, they revealed nothing unusual or of concern. They all had a fairly similar look. No plug stood out as being noticeably different than the others. They all had tinted brown porcelain near the tips with a hint of sandy char on the hooks indicating the engine burns a little oil which most likely is from oil in the PCV air. The gaps were all pretty large, but not overly so...plenty of tip still showing although rounded as you'd expect from a copper plug. I believe brand new, they were .055", so the gaps weren't exactly narrow to start with.

Plugs1-4

MI_03112021_132628.jpg (39.1 KiB) Viewed 5898 times

Plugs1-4, view2

MI_03112021_132559.jpg (31.22 KiB) Viewed 5898 times

Plugs 5-8

MI_03112021_132529.jpg (26.96 KiB) Viewed 5898 times

Plugs 5-8, view2

MI_03112021_132412.jpg (32.62 KiB) Viewed 5898 times

Otherwise, they don't really look bad...just a bit used (~41kmiles).

Being the engine isn't boosted and has a CD ignition box (SUM‑850610), jumping a large gap shouldn't have been a problem which is probably why I never experienced misfires. Although I guess the larger gap could add more randomness to where the spark jumps on each fire and that MIGHT account for rough engine running? For those experienced, how likely is that? Or is there something else that's more likely? I don't see nearly enough coating/glazing to cause the spark to travel to the side or up the porcelain.

Anyway, I put the Platinums back in which were in great shape and didn't have 1/2 the browning the copper plugs are showing. But like the 103s, they still were gapped for Stock Explorer 302 specs of .055". Being this is a high compression 331 stroker, I closed the gap down to .040" on all 8 before installing them and actually measured each using a gap gauge. The engine is back to running noticeably smoother. I've only driven it a few times, but so far, the plug replacement seems to have improved driveability...no difference in hard-accel that I can tell. Based on the pics, does anybody have any words of wisdom they can share about what these plugs might've been doing and why?

On a slight tangent, notice how the brown spots are not on the same place of the porcelain relative to the hook. I'm assuming the location of the brown spot is relative to where the intake valve was when the plug was installed.
Do the plug mfgs make any effort to locate the hook electrode relative to the threads?
Do the car/head mfgs do anything to ensure plug landings and threads are consistent cylinder-to-cylinder and head-to-head?

Obviously NOT to one or both in the case of this set of plugs & my 90s era GT40p heads. But the need for precision & consistency in modern engines is much higher than it used to be. I thought perhaps somebody might know if modern engine components consider details like where the hook will be in the combustion chamber.

[LeadHead]

I looked at a bunch of different pictures of spark plugs, and it appears that the thread starts are pretty random.

I know it used to be (or still is?) an old racer's trick to have different thickness washers to put under a spark plug to get the electrode in an optimal position.

[cgrey8]

I looked at a bunch of different pictures of spark plugs, and it appears that the thread starts are pretty random...

That's kinda what I was suspecting, at least as it relates to plugs intended for my generation of head.

...I know it used to be (or still is?) an old racer's trick to have different thickness washers to put under a spark plug to get the electrode in an optimal position.

Back when I had the heads off the engine, I took my plugs and test-fit them into various cylinders to see where each one put the hook. I tried to find a combination that would locate the hook closest to the top of the cylinder in an effort to keep it out of the incoming airflow as much as possible. Is that what the strategy was for the old racers using the washers? If not, what was the intention/strategy they were trying to accomplish with the washers?

[LeadHead]

No idea. I think maybe to have the open end point into the chamber?

[jamie from oz]

hi.
on the E-tec outboard motors the spark plugs are indexed to a particular angle to help the ignition flame propagation and for the direct injection fuel spray pattern from memory .
the plugs have a line marked on them and if the line doesn't fall into a particular zone you try another plug from the carton .
I have used 10 plugs to get the 6 plugs into the specified index zone .
my conclusion to this is yes it dose matter in hi performance for that last 0.1% but for street cars/trucks it would not make any difference.

Jamie