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Discussion Starter · #1 ·
I have a 2016 Challenger RT. I'm at about 30000 miles and decided it'd be a good idea to just check up on the spark plugs (NGK iridium spark plugs LZFR5CI-11), especially since I'm not doing anything else over this quarantine. When I finally took out all the spark plugs, all 16 spark plugs were completely carbon fouled. Just dry, pitch-black soot on the top. These plugs should be good for much longer than 30000 miles, but I went ahead and ordered new ones after seeing how badly carbon fouled they were.

My theory is that because I went catless without a tune and without O2 simulators/spacers (have been running with the CEL on for about 2-3 months) it screwed up the air-fuel ratio from the O2 sensors and caused the engine to run really rich, which ultimately caused the carbon-fouled spark plugs.

Does this sound at all plausible? I don't know a whole lot about cars and I'm still trying to learn as much as I can, but I can't think of any other reason why the spark plugs are this messed up just after 30000 miles (I occasionally have fun with the car and drive it a bit hard, I must admit, but I try not to do it all that often). If this is the reason, would getting O2 simulators/spacers fix the issue and air-fuel ratio?

Any advice or feedback is appreciated. Thank you!
 

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2020 Dodge Challenger Hellraisin Scat Pack
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I have a 2016 Challenger RT. I'm at about 30000 miles and decided it'd be a good idea to just check up on the spark plugs (NGK iridium spark plugs LZFR5CI-11), especially since I'm not doing anything else over this quarantine. When I finally took out all the spark plugs, all 16 spark plugs were completely carbon fouled. Just dry, pitch-black soot on the top. These plugs should be good for much longer than 30000 miles, but I went ahead and ordered new ones after seeing how badly carbon fouled they were.

My theory is that because I went catless without a tune and without O2 simulators/spacers (have been running with the CEL on for about 2-3 months) it screwed up the air-fuel ratio from the O2 sensors and caused the engine to run really rich, which ultimately caused the carbon-fouled spark plugs.

Does this sound at all plausible? I don't know a whole lot about cars and I'm still trying to learn as much as I can, but I can't think of any other reason why the spark plugs are this messed up just after 30000 miles (I occasionally have fun with the car and drive it a bit hard, I must admit, but I try not to do it all that often). If this is the reason, would getting O2 simulators/spacers fix the issue and air-fuel ratio?

Any advice or feedback is appreciated. Thank you!
Possible. The converters are monitored by O2 sensors. The readings from these are used to fine tune the fueling. If the converters are not operating correctly, or have been removed in your case, or if the sensors are not operating correctly the engine controller will attempt to adjust the fueling to get post converter O2 sensor voltage readings it expects. If it doesn't it turns on the CEL and logs one or more error codes. In the meantime the fueling is not optimum and could be rich. The long term fuel trims could provide a clue as to whether the engine controller is adding fuel or subtracting fuel.

Another possible explanation is if the plugs are not factory plugs they are too cold or do not have the right tip to help the plugs run clean in low speed operation.

Added: My advice would be to install the cats, return the exhaust system back to factory. Replace the plugs with factory plugs. Be sure they are gapped correctly.

Hopefully the engine controller will then get the sensor readings it expects and the engine will be fueled correctly and run better for it and plug life will be up to par and the CEL will remain dark.
 

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Ive got no cats and run extensions til i have it tuned. Run the iridium plugs also. Have no issues. The rear 02's primarily read the difference from front 02's to check the efficiency of the cats. You need to scan it and see if you have any other codes. Sounds like either upstream 02 is bad or map sensor is bad. Run the extensions til you can get it tuned, then just turn off the rear 02's altogether.
Is it stock exhaust or Lt's?
 

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Discussion Starter · #6 ·
Ive got no cats and run extensions til i have it tuned. Run the iridium plugs also. Have no issues. The rear 02's primarily read the difference from front 02's to check the efficiency of the cats. You need to scan it and see if you have any other codes. Sounds like either upstream 02 is bad or map sensor is bad. Run the extensions til you can get it tuned, then just turn off the rear 02's altogether.
Is it stock exhaust or Lt's?
I am running a stock exhaust.

Thanks for the info - it sounds like running extensions seems to help a lot, more than I thought they would. I'm going to start looking into some extensions from bigdaddies as I heard a lot of good things about them.
 

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I am running a stock exhaust.

Thanks for the info - it sounds like running extensions seems to help a lot, more than I thought they would. I'm going to start looking into some extensions from bigdaddies as I heard a lot of good things about them.
Just get them off of ebay. Just make sure they have the small hole. Some have a big hole and wont do the job. You only want the 02 to sniff a fraction of the exhaust gas. Shouldnt be over 5.00 each.
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