What your Spark Plugs can tell you

What your Spark Plugs can tell you

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1979 CJ-7 with a fiberglass body and 1982 wide track axles, 258 I-6 with a 1995 4.0 head, HEI distributor, Motorcraft 2100 Carb, T-18 wide ratio tranny, Super Lift Springs and 33s, a 1997 BMW 328i, and a 2010 REDLINE CONQUEST TEAM Cyclocross Bike. :)
For those that don't know about this, you can tell a lot about how your engine is tuned by reading your spark plugs. The obvious one is black oil fouled from worn out rings, valve seals or valve guides, but you can also tell if your carb is jetted too rich or too lean, if your ignition timing has too much or too little advance, and if you need to run a hotter or colder plug.

I found this great web site that shows a variety of pictures with captions telling what they mean.

Have a nice day!

Spark Plugs
 
Thanks for the post. A lot more detail here than in most manuals.

Tommy
 
Yes that is a good picture guide of spark plug read plugs by colors...
I have been using the same one in tech use for 3 yrs or so.


The spark plug ground strap can be used for temp range indication. I think I posted this a few days ago on this forum.. The above link does not cover it... but cool thing to know. The ground strap will have a "color change" about 1/2 way along the length of strap... If the color moves twords the electrode its cold and if moves twords the threads its too hot. Middle third of length is where it should be.

This if FINE TUNE type stuff when looking at the ground strap unless its at the very ends. I use it when looking at engine advance and time.....

Too Much time will allow the combustion gas to be in cylinder longer..... Chamber...gets hotter and strap mark will move twords the threads.

Too little advance and you may let the combustion gas go before its done all its work and little too soon and will be cooler combustion / cylinder temps and the strap color mark moves twords the electrode....

TWO things to note....
HEI fans here usually have lots and most likely toooooo much advance... Look at your gound strap it most likely shows kinda hot. More fuel can cool it off up to a point... to much fuel and it keeps buriing and can make stuff too hot and more hot.

I would not and most jeepers will never change spark plug heat range. This is more advance stuff and if stock engine USER / Forum Member feels plug heat range change is necessary.... somthing else is wrong and needs to be corrected....

The spark plug is a MAJOR HEAT SINK for the combustion chamber. Nitros, blowers, not having a normal aspirated engine, change of fuels are the reasons heat ranges are changed. If we run a normal engine the stock plug, I & My Teachers recommend normal autolite copper plug for the AMC Jeep Engines... they run the best and past tests out of new box the most often. Lots of plugs are bad out of box so after a tune up take a look in a few days... could have a bad plug in there and the color may tell you so.

Always look at your plugs... its also how I tuned my carb.

Can search..... "reading spark plugs"
This search will show you many links on web.
 
Yes that is a good picture guide of spark plug read plugs by colors...
I have been using the same one in tech use for 3 yrs or so.


The spark plug ground strap can be used for temp range indication. I think I posted this a few days ago on this forum.. The above link does not cover it... but cool thing to know. The ground strap will have a "color change" about 1/2 way along the length of strap... If the color moves twords the electrode its cold and if moves twords the threads its too hot. Middle third of length is where it should be.

This if FINE TUNE type stuff when looking at the ground strap unless its at the very ends. I use it when looking at engine advance and time.....

Too Much time will allow the combustion gas to be in cylinder longer..... Chamber...gets hotter and strap mark will move twords the threads.

Too little advance and you may let the combustion gas go before its done all its work and little too soon and will be cooler combustion / cylinder temps and the strap color mark moves twords the electrode....

TWO things to note....
HEI fans here usually have lots and most likely toooooo much advance... Look at your gound strap it most likely shows kinda hot. More fuel can cool it off up to a point... to much fuel and it keeps buriing and can make stuff too hot and more hot.

I would not and most jeepers will never change spark plug heat range. This is more advance stuff and if stock engine USER / Forum Member feels plug heat range change is necessary.... somthing else is wrong and needs to be corrected....

The spark plug is a MAJOR HEAT SINK for the combustion chamber. Nitros, blowers, not having a normal aspirated engine, change of fuels are the reasons heat ranges are changed. If we run a normal engine the stock plug, I & My Teachers recommend normal autolite copper plug for the AMC Jeep Engines... they run the best and past tests out of new box the most often. Lots of plugs are bad out of box so after a tune up take a look in a few days... could have a bad plug in there and the color may tell you so.

Always look at your plugs... its also how I tuned my carb.

Can search..... "reading spark plugs"
This search will show you many links on web.

Good info. I'd never read that coloration at certain points along the ground strap can teach us things. I was running stock Autolites in my old configuration, but when I swapped heads and had the increase in compression that goes with the smaller chambers, I switched to a cooler heat range as is recommended. I also switched to Champion because I've always had good luck with them. Personal preference. On my Vette when I was running nitrous oxide I also ran a cooler plug and I indexed them so the gap and therefore the spark kernel was facing the valves. This can add a few horse power to performance engines by more easily igniting the charge for a more complete burn. I saw a consistent gain of almost 2/10ths of a second and 2 mph extra in the traps in the quarter mile when I indexed the plugs. :D
 
this is a great post thank you. My plugs look just fine. One question, the "Rich" plugs are described as resulting from mixtures of 10 to 1 and a EFI will work at maintaining a 14.7: 1 ratio. Kind of makes you want to say Hmmmmmm.:cool:
 
Yey 14.7 gets uses a lot....

Not sure if the EFI maintains that A/F ratio or not.

Will take a guess that at hyw cruise it gets much leaner, and with that the temps go way down too. I am not sure if EFI does this or not.... I would guess to get the HIGH hwy mpg, this does happen and many may not know. I have never dug into this to find out.

I now there are some very good carb tuners, some of the weber guys I have found in the few years of reading everthing I could find on the subject.... The carbs it is very well accepted to lean out the hwy cruise.... power is not needed, the cylinder temps go way down, and with the mech adv way in, the vac levels usually high so the vac adv is pretty high.

This is a very hard concept to understand. The airplane engine charts for small planes is a good ref. The pilots of small planes
 
I need to poor coffee in the other ear. 14.7:1 is much leaner that 10:1.
 
I need to poor coffee in the other ear. 14.7:1 is much leaner that 10:1.
There's an easy way to tell exactly what it's doing. Do you know anyone that owns a wide band? If so, you can have an exhaust shop weld in a spare bung after the manifold and with a spare O2 sensor and a wide band, you can drive it around and read what mixture your running in all the different conditions. I plan to do just that one of these days since my buddy Jimmy just happens to still have a good wide band sitting around. Reading plugs will get you in the ball park, a wide band will tell you exactly what your mixture is doing.
 
I need to poor coffee in the other ear. 14.7:1 is much leaner that 10:1.

Question? going thru emails and read again... this is a coffee question?
YES, it take more air volume to explode a small amount of fuel. 10:1 would be the richer mix.... one side will stay 1 so we can compaire with a look and not do the math. 1/4 teaspoon of fuel has lots of energy

Right??...


What I said above is the HWY CRUSE can be pretty lean... and will be above the 14.7:1 . The 14.7 number will be bigger and a opposite thing happens too... the temps of cylinder drop too. If remember right it can get to the 16:1 range.... Usually we think 14.7 is the ratio we want.... get leaner it get hotter, get toooooo rich it gets hotter too.... HYw Cruise is the odd ball... this is one of the things WEBERs do well.

these are big pot of coffee items....

also a reason I stayed stock engine ... AMC gave me the curve. Change cam, valve train, compression, and the advance curve is now a custom and will take more than I have to get it right. The guys I know that can do are 1100 miles away.. so I stayed stock and used the AMC advance.
 
Question? going thru emails and read again... this is a coffee question?
YES, it take more air volume to explode a small amount of fuel. 10:1 would be the richer mix.... one side will stay 1 so we can compaire with a look and not do the math. 1/4 teaspoon of fuel has lots of energy

Right??...


What I said above is the HWY CRUSE can be pretty lean... and will be above the 14.7:1 . The 14.7 number will be bigger and a opposite thing happens too... the temps of cylinder drop too. If remember right it can get to the 16:1 range.... Usually we think 14.7 is the ratio we want.... get leaner it get hotter, get toooooo rich it gets hotter too.... HYw Cruise is the odd ball... this is one of the things WEBERs do well.

these are big pot of coffee items....

also a reason I stayed stock engine ... AMC gave me the curve. Change cam, valve train, compression, and the advance curve is now a custom and will take more than I have to get it right. The guys I know that can do are 1100 miles away.. so I stayed stock and used the AMC advance.
There's always tuning on the dyno. We have MC Racing locally that can hook you up and put a sniffer in the exhaust and help you get it exactly right. Pretty much all they do is tune heavily modified engines and install pro charger blowers. It would cost a couple hundred for the dyno time, but it might be worth it.
 
We have the dyno boys here too. Might laugh when I pull up with a 110 HP CJ with a tractor engine that maxes out at 4400 rpms. Many of us here have hard time getting to 3500 rpms. Some of us do not have tacs and may not know they at what level they rev to.

Dyno....Not sure they will help you with getting the advance curve set right... the tech are into FI and computer curves. I kinda doubt.

Dyno..If the valve train is not right.. dyno going to do some damage maybe or likely.

I may do it/dyno someday to see where I am... guess stock is 110 HP and I might have 140 but its not a lot.

For now... I kinda understand how the webers work. I have mine tune pretty well, no flats, roars, great economy. Can also rent widebands and see how close... I know its close.

Fred




Neighbor has nice 69 camaro with marine FI engine. Solid race and street drive and just tighten up bolts every few wks. Camaro shakes my home and air from 250 ft. He wanted more... put big blower and has been farting around with widebands, laptops, dynos, strip for 1.5 yrs now... This will be 3rd summer and he may get it just right this summer.
 
We have the dyno boys here too. Might laugh when I pull up with a 110 HP CJ with a tractor engine that maxes out at 4400 rpms. Many of us here have hard time getting to 3500 rpms. Some of us do not have tacs and may not know they at what level they rev to.

Dyno....Not sure they will help you with getting the advance curve set right... the tech are into FI and computer curves. I kinda doubt.

Dyno..If the valve train is not right.. dyno going to do some damage maybe or likely.

I may do it/dyno someday to see where I am... guess stock is 110 HP and I might have 140 but its not a lot.

For now... I kinda understand how the webers work. I have mine tune pretty well, no flats, roars, great economy. Can also rent widebands and see how close... I know its close.

Fred
I never thought about trying to rent a wide band. If it can be done cheap, I'd suggest that to anyone on here that's changed carbs, They sell O2 sensor bungs in the help section at a lot of parts stores, and any muffler shop will weld it in for only a few bucks. Then you just have to worry about getting hold of a working 2 wire O2 sensor because I would be surprised if they supply that with the rental wide band.

I'm lucky to have a good friend that owns an auto repair shop that has one.
 
The wide band does not make it that easy... Still need to have skills and the cruve/results on the A/F you want. How do you adj carb to get the results. Widebands can be rented, they come with the correct O2 sensor. The process still takes skill and understanding

update and fix ignition and /or advanc curve... Need the wide band again and will most likely be lean again....

I had to rejet and tune after adding the MSD.... made me too lean.

We have pretty simple stuff, most of us, fix the ignition curve, fix the weak grounds, add the manifold heaters if not hooked up, do the TeamRush so you can get the better spark energy to the cylinder and the right one.......get back to the correct base line. These CJs have been / seen the same carbs so if HEALTHY the jets some suggest will be close.
 
P.S. I use to be just like your neighbor with my 1969 Corvette. :D
 
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The wide band does not make it that easy... Still need to have skills and the cruve/results on the A/F you want. How do you adj carb to get the results. Widebands can be rented, they come with the correct O2 sensor. The process still takes skill and understanding

update and fix ignition and /or advanc curve... Need the wide band again and will most likely be lean again....

I had to rejet and tune after adding the MSD.... made me too lean.

We have pretty simple stuff, most of us, fix the ignition curve, fix the weak grounds, add the manifold heaters if not hooked up, do the TeamRush so you can get the better spark energy to the cylinder and the right one.......get back to the correct base line. These CJs have been / seen the same carbs so if HEALTHY the jets some suggest will be close.
Jets and power valve. It's that simple.
 

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