Can worn out plain copper spark plugs cause a slight rich condition?

[IUP99snake]

Will a worn set of copper plugs affect the air fuel ratio?

Over the course of a month or two, I noticed that the average air fuel ratio during idle and part throttle driving has become slightly more rich than it used to be.

According to my AEM Wideband Failsafe gauge the air fuel ratio used to show between 14.0 and 15.0 (closer to 14.6-14.7 most of the time) during idle and part-throttle cruising on the highway. Now, it averages about 1 point lower, 13.0-14.0 (closer to 13.6 to 14.6 most of the time) under the same driving conditions.

Since installing the procharger a long time ago, I've always run plain copper plugs and changed them about every 10K miles or so because they wear out much sooner than platinum tipped plugs, even if they aren't actually "fouled".

I know I'm due to change my plugs, it's been a good 11,000 miles at least since I last changed them.

Although the power and driveability haven't deteriorated, I'm wondering if old worn copper plugs can cause the type of condition I'm experiencing.

My wideband gauge is newer than my current set of plugs so I have no idea how the air fuel ratio may be affected over the lifespan of copper plugs. Since I didn't have the wideband before, I would have never noticed if it was running slightly richer when my plugs near the end of their lifespan.

 

[IUP99snake]

Here's some additional info about my troubleshooting process so far:

I haven't noticed a significant change in my fuel economy despite the slightly richer AFR. I recently made a 250 mile trip to Tallahassee that I've made many times before. I got about the same mileage and had the same amount of gas left over in my tank after the trip.

I haven't made any changes or modifications to the engine during that time period. However, to try and remedy the issue, I tried washing out the air filter, cleaning the MAF using the specific cleaning spray, and checking for vacuum leaks.

I know that bad 02 sensors can cause a rich condition. While I do have old upstream 02 sensors, I don't think they are bad. The upstream sensors are performing normally according to my OBDII datalogger which shows the voltage data plotted on a graph to show the normal fluctuations in voltage.

But I may be wrong about the 02 sensors.. I don't know if they can cause a rich condition even if they display the right data. (If someone thinks it may be the 02 sensors, I'll post a picture of the graph and other data so we can examine it in greater detail).

My wideband sensor is mounted in an existing bung after the X in my off-road X pipe where one of the old downstream senors used to be until they were turned off. Since I used an existing bung, the AEM sensor is mounted at the proper angle such as to not allow water to collect in it. I haven't changed the location... But perhaps there might be a slight degradation in the sensor? (it's less than a year old)

I'm pretty sure I don't have any vacuum leaks, my analog boost/vac gauge reads 22 in/hg at idle, which is the same as before.

But I can use my AEM Wideband failsafe gauge (which also reads boost/vac and RPM) to compare some really detailed datalog files from before and after to see if there are any changes in vacuum which might be causing this. I'll post an update later tonight about this...

Hell, copper plugs are so cheap, I might as well just pick up a set on my way home from work and change them...

 

[01Jes]

Having the same issue with a buddies cobra however it's 2 points more rich than yours. His AFR idles around 12.0. I found a pinched line behind the whipple but only yielded a small change. Could be a faulty AFR gauge, so we are going to datalog STFT's at idle and if they are off 1.0 the car is truly reading rich. Gonna change his plugs Tom also. Also curious if bad 1st stream 02's could cause this problem.

I also have my AFR sensor 02 in the 2nd stream bung. No cats for me and she idles 14.6.