[AspiringCarGuy]

Just curious if anyone has had to replace their stock catalytic converters. I've got an '18 ZL1, completely stock, 50k+ miles. It's my daily driver and I do about 10 two-day track events a year. Late in the 2020 season at Watkins Glen, I was way down on power. Foot to the floor, could not go over about 4K RPM in 3rd. As I was bringing it in, the check stabilitrak message came on, there was a service rear axle message, a CEL, and codes P0420 (catalyst system efficiency below threshold), P0455 (evap system), and P0302 (misfire cylinder 2). It was running rough and sounded, for lack of a better description, like it was congested. Revving the engine in the paddock, it was real slow to climb through the RPM range. Long story short, after 4+ months at the dealer, two return trips to the dealer, new lifters, new O2 sensors, new head gaskets, new ECM, new fuel injector on #2 cylinder, it was finally determined that I had melted the cats and the increased exhaust back pressure was causing the engine-related issues. They finally relented and replaced the primary and secondary cats on bank 2, and the secondary on bank 1. Total bill for all of that was north of $10k- fortunately all covered under warranty. The primary CAT alone has a list price of $8350, sale price of $5000. I also had the oil pump issue (see https://www.camaro6.com/forums/showthread.php?t=532023). Total warranty work is $15k+.

Questions: am I just unlucky with this cat problem, or have others seen this? Will these cats hold up to years of track driving, or am I looking at $10K worth of cats every 3-4 years? that's one heck of a consumable...

Post Script: public service announcement. In researching all this, I learned that the Clean Air Act as amended in 1990 requires auto manufacturers to warranty emissions equipment: "major emission control components are covered for the first 8 years or 80,000 miles (whichever first occurs). The specified major emission control components only include the catalytic converters, the electronic emissions control unit or computer (ECU), and the onboard emissions diagnostic (OBD) device or computer." [see https://www.epa.gov/transportation-a...%20as%20well.] However, you must live in an area that requires emissions testing compliant to the federal standards. Living in Maryland, that is most definitely the case. Florida residents- with no required emissions or safety inspections, you may not be covered. As always, YMMV.

[m6-lt1]

First off, cats are NOT 5k dollars. Idk why your dealer listed it at that cost but that is not what they cost. Below is a link that shows each side cat for your car is a little over 500 bucks. I do believe you just got unlucky.

https://www.gmpartsdirect.com/v-2018...ust-components

[Blueclyde]

Whatever caused the misfire is what caused the catalyst to fail. A misfire can send unturned fuel into the exhaust system where it will burn in the catalyst in an uncontrolled manner. This will drive catalyst temperatures up and melt the cordierite material that the monolith is made from. The catalyst was the victim and not the cause.

[GRUF78]

Sir,

Sounds similar to my car:

2018 ZL1 1LE bought for track/DE events for wife. Oil pump failure at 6300 miles. GM replaced the short block. With new " engine", car uses 50% more fuel in a 20 minute track session (~9 gallons) than previously. At 6500 miles, left main cat fails and is replaced by GM. At 8500 miles, left main cat fails again-replaced by GM. At 9400 miles, left main cat fails again- replaced by GM. The engine has never been tuned. The car has an AWE track exhaust and a Rotofab intake and has since right after purchase..I.E,..the original engine ran with both of these mods for ~5K miles with no issues.

Additionally, after the new engine , the exhaust heat from the car has exponentially increased to the point of MELTING 3 sets of rear valance reflectors, the license plate illumination lamp and warping both rear tail light assemblies. Also, 2 sets of left bank exhaust bolts and studs have fallen out during this time. The black exhaust tips on the AWE exhaust have turned blue from the heat.

Dealer has run numerous diagnostics and all of the system and according to them, have checked good. They are trying to blame the aftermarket exhaust for the heat damage....


I believe the car is is over fueling a cylinder in the left bank somehow. However, the O2 sensors are good and no codes.

Thoughts? Thank you,

JM

[AspiringCarGuy]

Thanks all for the input. Very helpful. GRUF78- that sounds like quite the saga. Good luck to you sir. The only data point I can offer is that I typically go through between 9-11 gallons of gas for a 20 minute track session. Sounds like your new engine is burning about as much fuel as mine. No idea why that would be 50% more than original engine.

m6-lt1- I went back and looked at the dealer invoice. I do see where it lists the cat, part number 022956560, for $752. Sounds about right given dealer markup. The $5000 item was listed as part number J-44175-A. The description is "no match". Odd. I can't find any part with that number. I have no idea what it is. I suppose it could be labor. There is a separate section of the invoice for labor. It says the tech was number 174, but there were 0.0 units (hours). So maybe labor for a warranty repair is recorded differently? Dunno. The invoice total was $6284.10, so it was something. But I do feel much better knowing that if this happens out of warranty, the cat is ~$500, and not $5k.