Spark plug #4, For Art Options

[Defgeph]

This is spark plug 4

[lagos]

Those plugs do look very good, John.

I remember a magazine I read a while back had a great article on reading plugs, setting gap, and what temp plugs to use for what sort of applications. Pretty good article.


I know its not a FI motor, but after changing spark plugs on my 5SFE you could see the white on the old ones indicating either a hot/lean motor condition. I put fresh new plugs in, and the condition looks identical.
I'm quite confident that this is due to me driving 60+ miles on the highway every day last year at about 80 MPH....at those engine speeds (~4,000 RPMS) and not delivering much fuel due to a low throttle position, my best instincts told me that this causes a plug to appear relatively lean even though I'm sure the factory tune is A-OK on the motor.

Unless the injectors or fuel filter are pretty clogged or theres a vacuum leak that causes a lean off-throttle condition to the fuel system, I would think that my plugs aren't a great indicator of my engine condition, no?

Jeff, maybe your vacuum leak could be causing the "lean plug" appearance both at idle and at while cruising on the highway at high RPMS where fuel consumption depends more on the vacuum present at the fuel rail??

reading plugs IS very tricky because certain parts of the plug tell you different things. so maybe the white you saw, was just fine. it could also just be a problem with the brand of plug or heat range that you used.

when you are cruising on the highway, you are at 14.7 afr (aka stoich). when u lift off the throttle, the car goes VERY lean. this is totally normal, and shouldn't show up on the plugs.

here are some good sites for plug reading

http://www.dragstuff.com/techarticles/how-to-read-plugs.html

http://www.maxracesoftware.com/spark_plugs.htm

This post has been edited by lagos: Oct 9, 2006 - 10:29 PM