i just changed my plugs to denso iridium... and was wondering how long after i changed it will i be able to tell whether i'm running lean or not.

These plugs when they're new they look white as snow (the center part), and i've been runing these plugs for about 2000 miles and the color hasn't changed.

let me know your thoughts...

 

yea chances are you are running lean.......i havent heard many good things about the denso iridiums......everybody is running the ngk-br7es on the evo VIII that I know of....

How is your idle when cold/hot?

 

I use NGKBPR8ES. 45K miles, no issues of running lean.

 

there is many different guides with pictures how to "read" plugs. I dont know about on here but there is some very good ones if you do a search on the internet. If the ceramic looks new and there is a little carbon on the outside ring your probaly good. if there is no carbon anywhere then your too lean.

 

If you're trying to judge your AFR from the plugs, don't. First, unless you've seriously screwed with the fuel maps you're never running lean (lambda > 1) under load. You can be running *leaner* than you should be, but you can't judge that from the plugs. At least not until you've actually damaged something.

If you're worried that changing the plugs can somehow make you run lean, don't. The only thing that affects the air/fuel ratio is, get this, the amount of air and fuel. Timing, spark plugs, phase of the moon can't change that.*

*OK, not completely true. What could happen when bad plugs cause repeated misfire? The front O2 sensor will see the "unused" oxygen and the ECU (in closed-loop) will think the mixture is lean and adjust the fuel trims to add more fuel. Note, a good WB O2 sensor will not be fooled in this situation.

Dave

 

Dave a misfire read by a WB 02 will be displayed as a lean too.
I posted a link to plug reading before, however I doubt you are willing to go through the proceedure. The critical wot reading may be destroyed by driving in cruise for any length of time.

The question is, why do you think you are running lean? Are you adjusting AFR?

 

Thanks all for your replies. Quick question... i don't see any metal specks on the pluggs itself but why do i see some like metallic shaving on the plug wires? I took off the spark plugs wire and saw like dust of metals shaving?

anyone care to explain why there are dust of metalic type of dust on the spark plug wires?

thanks

 

It shouldn't unless you're getting a lot misfiring or the catalyst in the diffusion cell is getting dirty. I guess I should qualify that I'm talking about occasional misfire under load when the mixture is rich.

The diffusion cell in a WB has a catalyst, just like a catalytic converter, that completes the combustion. In a rich mixture the pump current to the WB drives oxygen into the cell. The greater the pump current necessary to reach stoichiometric in the diffusion cell, the richer the mixture. For a lean mixture pump current of opposite polarity drives "excess" O2 out of the cell. For an occasional misfire under load you have a hot exhaust with lots of active species (free radicals and such) and a little free O2 and unburned gas. They'll wind up getting together in the diffusion cell. If you have significant misfiring (but you'd know that was happening anyway) then there's probably too much O2 around to be used up in the cell. A narrow band of course is only sensitive to the level of O2 in the exhaust.

Dave