While recently checking my plugs I noticed that #1 and #2 looked normal, #3 was a little white and #4 was whiter than I've ever personaly seen in my cars.

Does anyone know why one or two of the cylinders would run lean? Can the ecu cause this or is it mechanical like a clogged or bad injector? Btw the overall air/fuel is very rich. Rich enough to worry about misfires, Could that make a plug look like it is running lean?

 

No, if you are truly running rich, the plug would be "sooty". A light tan is what you should be looking for.

 

I've understood 'biscut' was ideal. That would be off white, short of tan?

 

White is water.
Not good.
Put your hand in front of the exhaust
pipe, after car is warmed up.
Wet = water, maybe a gasket going?
Then check oil dip stick for a foam on it.
Also = water.

 

It's not like it runs rich all the time. It is definitely running rich at full throttle, off the charts sub 10's at some points. But the #4 still looks a little too white.

I'm wondering because at a recent dyno day my numbers were all over the place. The car drives great on the road, I took one of the techs on a test drive between runs just to make sure it was ok. He commented on how quick it was and we went for round two. still didn't seem right on the dyno though.

I was thinking that if one cylinder was lean it might knock and cause the ecu to run every cylinder rich. I'm not sure how it works though.

I guess I'll give it a compression test and start from there.

 

Frisco,

When you say gasket, do you mean the head gasket, the manifold gasket, exhaust gasket??..

Please elaborate, since my exhaust has alot of water coming out of it and the plugs tend to ben tan-brown when pulled out of the car. My car's getting a new head and erverything soon anyway, but I thought that more detail would be useful for me and other users especially :smile:

Henry

 

I think he meant head gasket. That would let coolant in and cause white plugs. Mine are mildly white, but I will check compression later today. If it was severe enough to let water through the exhaust I think you would have obvious drivability and smoke problems. Plus there is always water coming out becuase of the catalytic converter anyway.

 

Thanks for the clarification, I really appreciate it

I guess that the majority of water coming from the exhaust is from the catalytic converter doing it's thing, and so I won't worry about that too much anymore :smile:

Henry