I’m also suspicious of the timing adjustment on the GEMS engine. Gervins ideas are definitely worth checking out. I also doubt that Seafoam would do anything. I don’t know, but would the performance cam in the 4.6 (as opposed to the stock 4.0) put your numbers over the edge?

 

Now that you mention it, I recall reading one poster who used one cam for inspections, then another for driving.

 

Well, looks like it may be the cats after all. The state provides free inspections by emissions specialists for those who fail their yearly test - just went in today and they ran some additional tests which found that fuel trim numbers were all perfectly healthy and it doesn't seem to be an air-fuel ratio issue. Apparently the cats are EPA but not CARB compliant.... which is a shame because the cats are brand new.

Interestingly, I called a really well-rated muffler shop in Boulder for a quote and the guy told me that his system wasn't showing any cats available for my year/make/model that meet colorado's standards. He's apparently run into this a few times and said he'd have to call the emissions office and ask them what part number would be acceptable / what they'd pass me for. Seems bizarre for a car that's "only" 25 years old - has anyone heard of anything like this before?

 

LR cats were particularly targeted by thieves because they are so substantial = lots of precious metals, and LR owners like to jack up the trucks so access is easy. Better cats will knock down NOX.

 

I also can't pass CO emissions. The emissions specialist also confirmed my cats are the issue. I figured it was a bad cat since some a-hole tried to steal the driver side cat and damaged it. It's been rattling off and on for a while.

I got a quote last summer from Boulder Muffler for new CARB cats at approx. $2500 installed for the pair. Sheesh! I declined since that's almost three times what I paid for this rig.

I've been looking for a local super cheap D1 with intact cats I can purchase for parts scavenging.

 

The Magnaflow site shows their CARB cats (445004) as out of stock. TLR4.6H8G1EK $554/ea. These are universal fit and must be welded in.
It looks like O'reilly has them in stock for a mere $859.99/ea. Good gawd!

 

Has anyone here ever utilized a Davico cat? Looks like a decent option and it could be self-installed. No welding, which is a huge plus (for me).

https://catalyticconverter.net/i-304...converter.html

CARB legal Direct fit converter
SKU: 102214
POSITION: Center
SKU:102214
Free Ground Shipping - Lower 48 states. Some exclusions may apply
$931.42

 

Boulder Muffler is who I called as well, they quoted me $1980 for the cheapest compatible option that's approved by the state for my D1. I asked for the part number and they're only $278 on RockAuto (link) but since it's illegal to installed used cats now in Colorado no one is willing to weld in parts that I provide myself. I'm contemplating driving an hour and a half up to Cheyenne to get it done - I'm guessing that would bring the cost down to $800-1000. I'll let you know if I go that route and it works. Are you failing for NOx as well?

Regarding putting in a used stock cat from another D1, can anyone explain to me why this would work? I would think that the stock cat on a vehicle manufactured in 1999 would still do a worse job of breaking down pollutants than a "merely" EPA-compliant one from 2023. Were OEM cats made to be CARB compliant even 25 years ago?

 

Did you check with the emissions inspector for approved part numbers for your D1? I'm still trying to understand why Boulder Muffler would say that they weren't seeing any approved options in their system / why they would need to contact the emissions office for a list. I'm kind of inclined to go with the AP / Eastern Catalytic part I linked above just so I have something to point to if it doesn't work out. (Not that I expect the state government to show any semblance of leniency if I replace the cats and still fail...)

 

I just put one of these 2mo ago. They fit like absolute **** out of the box and I had to have a shop rework them and grind them flat. Admittedly mine were EPA vs CARB, but still was exhaust leak hell right off the headers when installed originally. Im also sure its too short because the olive at the back is hilariously leaking as well.