I rebuilt the motor of a 97 4.0 and put iy in my 2000. I ditched the pre cats and only left the rear. I just put the cat on today and it's glowing red hot. I put the o2 sensors in after the cat. Everything is hooked up but I can't figure out why this cat is over heating. I need help guys

Was it a new cat? Could be clogged if not…

It hapened 2 times now first was a new one this time is with the original

Any idea what the EGT is? Any signs or running lean/rich?

what is EGT? Also it had a code for an o2 sensor and running lean. I have the battery unhooked now to erase any memory

This is it glowing it smells bad too

Code for running lean means PCM is commanding rich. Probably throwing the code because yer out of the 30%ish LTFT limit. Most likely you have the O2 sensors in wrong location or ommitted? You could be washing down the cylinders of your new rebuild. If it's the Rotten egg smell the cat might be irreversibly damaged.

Precat O2 sensor voltage toggles low to high. If installed post cat it won't toggle due to the cat doing its job. The post cat O2 sensors are there to monitor the cat doing it's job. If the precat O2 is removed it won't toggle as well. Narrow band O2 needs to toggle since the PCM monitor has an algorithym to determine average precat A/F. If the sensor ages and toggles slow AKA "sluggish O2 sensor" the algorithym calculates and adjusts A/F incorrectly

Smell your dipstick. If it stinks like gas, problem. Regardless MPG probably wont be good and power will suffer if too rich.

I'm pretty sure my 97 the o2 sensors were before the cat so maybe that could be a problem

my sensors were mix matched

Need the primary o2 sensor before the cat. Like in the header or downpipe. Secondary o2 goes after cat.

Yeah that's my set up. 2 in header and 2 after the cat

It is against federal law to remove a cat, and against forum rules to talk about doing so. Stick to the topic of solving the problem.


OP if your CAT is red hot, one of 2 things is happening...

1) Your CAT is clogged and needs to be replaced. Why is it clogged? Because you're probably burning oil, or see below....
2) One of your injectors is likely stuck open or a cylinder is misfiring, dumping raw unburnt fuel into the exhaust where it gets ignited in the CAT, effectively melting the catalyst inside.

FIX THE ISSUE, stop trying to bypass sensors that are necessary for your engine to run correctly and efficiently.

Fist step to fixing my issue is getting my daily driver street legal again so I can see what fixes fix my issue either way the cat has to be replaced