Really need help understanding why these plugs look so bad after 400 miles. #6 only has 40 miles. Thanks!

 

Bad upstream O2 sensors maybe? Is she throwing codes and running like crap?

 

Threw a code when #7 crapped out and then again when #6 fouled. Other than that nothing.

 

Did you happen to capture which codes they were?

If you have original O2 sensors it could be they are shot and causing this. Bad O2's have been known to cause this with plugs and not throw codes for some in the C5.

I've not had this occur with any of my C5's but I did have this occur with my BMW 645 and it was the upstream O2's causing it.

 

Looks like it's running a little rich...are the fouled ones all on one bank or is those pictures your #6 ??...need help determining who's who...if you have a scan tool look at that upstream O2...if it's not switching normally between 200-800mv but stuck below 450mv it will run rich like that...a few months ago my bank 1 was stuck at 100mv and my garage really stunk from that rich mixture.

 

Those are my current plugs...the #6 fouled last week and what you see is one weeks worth of driving. The rest of the plugs have less than. 500 miles

 

Are those the cylinders written down behind each picture ??…best if you have a scan tool to see what your O2 sensors and fuel trims look like….do the plugs smell more like gas or oil ??…oil fouled plugs look shinier.

 

yes those numbers correspond with the plugs. Only #6 smells like gas to me.

 

I recommend get a wideband and learn how to read the wideband sensor so you can diagnose the a/f ratio consistently while you drive and for the lifespan of the vehicle and all future vehicles.

Generally you will need to diagnose the closed loop feature of the narrowband. Determine whether the O2 sensors are switching while you drive.
This is how they work


Here is another one. Note they are not exact or very accurate.




That is why we use wideband sensors for performance vehicles. A wideband has a narrowband inside it, just superior control exterior electronics to detect a range of a/f ratio instead of just 1 specific a/f ratio.

The narrowbands need to switch from "LOW" to "HIGH" as they are intended to operate as digital devices. "LOW" is anywhere say 0.005v to 0.155volts~. "HIGH" is say .885v to 1.005v. All narrowbands during closed loop switch from "HIGH" to "LOW" and back to "HIGH" constantly, never ending, this centers a/f ratio around 14.7 in theory. But the sensors are averaging all cylinders, so for example if 1 injector is leaking fuel, that one cylinder will read rich, causing the O2 sensor to read rich, which will lean out all other cylinders to compensate. You will wind up with 1 rich and 3 lean on that side. And visca versa if a injector is clogged, all cylinders will enrich on that side. So if you found 1 rich plug and 3 white plugs this is probably the issue. If all plugs on a side are rich/dark/black/carbon coated then possible the O2 sensor is stuck "LOW" which tells the ECU to enrichment those cylinders for idle/cruise to a maximum value.

 

Do you have a scan tool and/or a 12 volt test light or maybe a fuel pressure gauge ??

 

You can have the guy at AutoZone, or whatever, plug in and scan for codes and translate it for you. It’s a free starting point.

Or, spend $100 for a local shop to hook it up for a full diagnosis.

 

Here's a log with just me idling until it warmed up. Anything look out of whack?

 

Can't open the file with that file extension...like I had mentioned see what your fuel trims look like and if you can "graph" your O2 sensors...other than guessing what part or parts to change that is the best I can do for you...and I don't like to guess...LOL !!

 

I do appreciate all of the help!