Can spark plugs that look healthy be sick?

I pose this question in my ongoing quest to improve performance on my 87 Dakota without spending unnecessarily.
Actually, it's not the spending that bothers me. I just don't feel like
changing my plugs. Condemn me for a lazy good-for-nothing if you will, but that's just the way it is today.
The reason I know that they look healthy is that every once in a while I pull one to see how it's doing.
Hello, plug How ya doin'? I come to watch your changing huin'
(huin' - slangy contraction of 'hueing', from 'hue', a gradation or variety of a color; tint)
The plugs have nice, unworn, square electrodes and are properly gapped and, over all, have a nice healthy appearance, albeit the ceramic insulators are a bit on the white side. Can I assume that they are in good shape? Or is there some internal condition, unseen by mortal eye, that can develop, that causes plug performance to deteriorate?
The truck idles a bit rough, nothing at all severe, but something that I think could be improved. I am ruling out the fuel delivery for the moment and concentrating on the ignition. The cap and rotor appear to be in good condition. The ignition wires all measure a bit below the low end of the resistance range as specified in the service manual, 250 to 600 ohms per inch. Mine are about 200 to 220 ohms per inch and are not that old.
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i would say if they look good, then they are good. and furthur more if it walks like a duck and quacks like a duck then....
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snipped-for-privacy@sasktel.net wrote:

Well, they don't walk and they don't quack, but I have seen them getting screwed. I don't know if it was like a duck. I've never seen ducks do it but, I'm sure it's on the internet somewhere.
--

Chuck Norris can fool all of the people all of the time and Chuck Norris
supports McCain.
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snipped-for-privacy@sasktel.net wrote in article

What does a bad spark plug resistor "look" like?
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* wrote:

Sometimes the insulator is quacked.
--
One meter, to within 0.0125% accuracy (off by just under .005 inches):
Three feet
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Like an open on the ohmmeter.
It's something that sure doesn't happen very often, though. Especially today when people just replace their plugs every once in a while rather than cleaning and regapping them. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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Simpson wrote:

Let's see an 87 V-6 no balance shaft with a crankshaft that wasn't the best design for smooth running. And it idles a bit rough. YUP sounds 100% normal to me. Think of the way that engine runs. The power pulses are not evenly spaced. Kind of like if you built a set of stairs, with every third step 15" tall. Think it might affect the way you run up them?
Oh and did I read that you have a MSD ignition on this truck? That isn't going to do much on a stock engine.
--
Steve W.
Near Cooperstown, New York
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Steve W. wrote:

This doesn't apply but I'll send it anyway.
Forgot the neon fuel line magnets. Cornering chrome. Blue dot tail lights. Aftermarket HID. "Turbo" cat backs. 21" rubber bands. Triple Platinums.
I guess we're all kids.
MOMMY!
No replacement for displacement, 4 valves and turbo chargers. Really, 4:11 gears. -- wws
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wstiefer wrote:

The MSD units do a great job IF you have an engine that needs them. A stock engine just won't need one. Now take an engine being force fed by a blower or a large turbo, one that develops enough cylinder pressure to almost pre-ignite the charge and you need the MSD to light it off and keep it lit because the mix will be dense enough that it will be hard to light with the single spark from a stock system. Of course you could always switch over to a Vertex nag and create a spark large enough to light up a small city!!!
--
Steve W.
Near Cooperstown, New York
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Steve W. wrote:

Just my luck, The one I bought used and resoldered some wires on stranded me. Soooo, sent it to MSD for repair. They redid my solder job(was perfectly ok) , tested it and sent it back. Same sh-t. '73 Mustang, 351 Cleveland, 3 angle valve job, gapless rings, Offy dual plane, Carter 750, Electronic distributor, port plates,etc. etc. I built the C-6 with torringtons and modified perf valve body, built the 9" with Richmond 411s and Detoit Locker. Don't have the time off the top of my head, but won a trophy first time out.
Just kids...........
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Usually a sick one will show in it's colour, like you describe your's showing a lean mix with their white ceramics.
With a modified carb and rough idle I also think lean miss. How did you set up your idle mix screws?
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos: http://mikeromainjeeptrips.shutterfly.com
Simpson wrote:

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Mike Romain wrote:

Hi, Mike... I use the Lean Best Idle method described here:
http://www.redlineweber.com/html/Tech/carburetor_set_up_and_lean_best_.htm
But even if I fatten up the idle mixture considerable, I still get a rough idle. I have read that a rough idle is common to this particular version of the Dodge/Chrysler 3.9L V6.
Steve W's first reply in this thread speaks to the nature of this engine that causes it to idle roughly:
"Let's see an 87 V-6 no balance shaft with a crankshaft that wasn't the best design for smooth running. And it idles a bit rough. YUP sounds 100% normal to me. Think of the way that engine runs. The power pulses are not evenly spaced. Kind of like if you built a set of stairs, with every third step 15" tall. Think it might affect the way you run up them?"
Aside from that, I had one instance recently where I was getting a comparatively stable idle as read by the tachometer function on a digital meter. I prepared the vehicle up for setting the idle speed as per the service manual. I used a digital meter and it fluctuated only between 70 and 71. You have to multiply the display times 10. Usually, it fluctuates between about 66 and 74.
For the life of me, I haven't been able to recreate that stability, but it was not that long ago so the ignition parts are probable not the reason. All indications point to the air/fuel condition.
I recently removed all vacuum hoses from the manifold vacuum and plugged up all ports. This would be for the air switch relief valve, the heater vent doors, purge solenoid bleed, vacuum kicker bleed for idle, electronic spark advance and the rough idle seemed to continue. To be sure, I should do it again and check with the tach meter.

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Simpson wrote:

Yup, sometimes there is just so much you can do to the old beasties...
The emissions sniffer gives me better readings by a 'whole bunch' with only 1/4 turn lean on both idle mix screws. Once is was a fail/pass difference, I got the retest on the spot. That gives the engine a little rumble at idle.
A little on the carbs can do a lot when you are right at the cusp of a perfect mix.
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos: http://mikeromainjeeptrips.shutterfly.com
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Sounds like it's lean to me. *Just barely* lean.
A.
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Unless you are using leaded gasoline or burning lube oil there is no color change, as there is no more ash. The lead in gas created lead bromide ash which lubricated the valves and valve seats. That ash appeared as a light tan deposit on the plugs. Eroded electrodes and anodes indicates over heated plugs, so if you are using the correct heat range, no or very low erosion will occur. So, the answer to your question is, yes, you can have a bad plug due to ceramic cracking, carbon tracking or resister failure and have it not be visible. Steve

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Steve Lusardi wrote:

That's interesting about the tan coloring no longer being an indicator of a healthy engine and a correct air fuel mixture. Someone needs to tell the writers of shop manuals. Leaded fuel began being phased out in the US in 1973 and have been totally banned for on-road vehicles for 12 years now.

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I know that and I agree with your observation of shop manuals. I build a lot of motors and now have to use a 4 gas analyzer to tune, as there are no visible indicators anymore on the plugs. You only see ash now with racing fuel. Steve

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Steve Lusardi wrote:

And all this time I have been sweating my pearly white insulators.
Damn... time to find something else to sweat over.

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