Spark Plug Analysis

[Lutrova]

For at least half a year now I've had a slightly rough idle. More recently I've noticed less power on acceleration, especially at lower speeds when I'd typically expect a bit more. On top of that there's been a jerk when letting off the accelerator pedal after mild acceleration. All of these things may be related, or separate issues. I've got a KOEO and CM code 34 "EVP circuit above the closed limit of 0.67 volts" as well on my less-than-1-year EGR valve and EGR position sensor.

Anyway, the main point of this thread is that I checked all the spark plugs yesterday, but I realized I don't have a lot of personal experience in analyzing them. They're Motorcraft AGSF44FM platinum plugs with around 15,000 miles currently on them. (I understand copper plugs may be better on these engines, but at the time I wasn't doing my own work and this is what my mechanic went with.) Pictures are here.

Cylinders 1, 6, and 7 looked like this. I believe this is normal wear.



Cylinder 3 had a lot of what smelled like oil on the threads and some carbon on the electrodes, but I don't believe there's enough buildup yet to cause issues?



Cylinder 8, as I've been warned, was the worst. Threads were completely covered and the electrodes and insulators have the beginnings of a crusty buildup. Is this what fouling looks like?



Cylinders 2,4, and 5 looked somewhere in between the first and second pictures. All plugs gapped at around .045", which I believe is stock. Insulators all looked fine.

My uneducated guess is that the valve stem seals are going bad on a couple cylinders, which is fouling some of the plugs and probably causing some other performance issues. I've seen plenty of search results for fouled plugs that look pretty bad. What I don't have a good understanding of is whether my worst plugs fall far enough on that spectrum to begin acting up, or maybe they've still got more time.

[Arquemann]

The first pic looks almost burnt, but the pics might just be a bit overexposed.
The plugs don't really look too black, those look more like just worn plugs. The deposit don't look particularly worrysome.

Oil on the threads means the oil came from the outside

[jaywish]

Did it run better after new plugs?

Also on #8 perhaps going up just one heat range on that individual plug range will keep it clean.

A coil with a slightly higher voltage output will supposedly handle the plats with no problem. Just a small upgrade.

[friskyfrankie]

When I got my '93 GM the previous owner had Autolite Plats installed but I am thinking about replacing them with the OEM ones from Motorcraft. There is some detonation so perhaps that might help. Going up in octane did not. Not a big fan of Autolites especially the more recent ones. I am thinking there is somewhat of a heat range mismatch with these plugs the OEM's might correct.

P.S. They did spark plug wires, at the same time, but I think they are Parts Master or some such nonsense so I have OEM wires that I would swap at the same time.

[Lutrova]

The cylinder heads are covered in decades of dirt, so I can't get a good look at what the plugs thread into. Is there some sort of o-ring or gasket that's supposed to help keep oil from seeping through? The threads on 8 are completely saturated, but where there's oil on the others it's mostly toward the end, which made me think the source was from inside.

When the plugs were changed they also did wires, cap, and rotor, but the coil was left. I've since replaced it anyway, but I wasn't aware there are differences in output or some sort of pairing between plug metals and coil.

[jaywish]

No gasket around the plugs in SBF. A bit more spark for the platinums.

[gadget73]

#8 is probably huffing oil, either from the PCV system or tired valve seals. One range hotter may or may not help. The rest look pretty normal honestly. Oil on the threads is probably leaky valve cover gasket. The very white look is pretty typical with EFI engines.

I've never been impressed with how platinum plugs run in these but that and a couple bucks might get you a coffee. I run copper on my stuff though.

[friskyfrankie]

#8 is probably huffing oil, either from the PCV system or tired valve seals. One range hotter may or may not help. The rest look pretty normal honestly. Oil on the threads is probably leaky valve cover gasket. The very white look is pretty typical with EFI engines.

I've never been impressed with how platinum plugs run in these but that and a couple bucks might get you a coffee. I run copper on my stuff though.

I think I tend to agree about running copper as opposed to the plats. So many projects - home and auto so I will get to it - eventually!

[Lutrova]

Good to hear most of the plugs look fine. Is there a chart somewhere that shows these levels of coils and spark plugs? Or a breakdown on the Motorcraft plug nomenclature? I'm willing to try something else on cylinder 8 given how cheap a single plug is. Hopefully it's the source of my rough idle and other little issues.

I've run it once before, but is the EEC-IV cylinder balance test precise enough to pick up on small misfires? Or is it intended for other things?

[Tiggie]

I spent a bit looking into the spark plug heat range question. AWSF44C is the stock plug, I think your closest Motorcraft in a hotter range is the AWSF54C, aka SP429. Spec'd for an 84-86 Ford LTD with a 3.8L.

http://jimsprojectgarage.weebly.com/motorcraft-spark-plug-information.html

[Lutrova]

That's a great chart, thank you. It looks like hotter plugs exist for coppers but may not for platinums. AGSF 54FM doesn't turn up any results.

I'm thinking switching to copper might be the way to go if the engine likes them better anyway and it lets me run a hotter plug on #8.

[jaywish]

Maybe you want to try it also on #3.

[jaywish]

Autolite ap2546