Ali SC3

iTrader: (10)

well yeah cause you dont normally have to replace the cats unless they go bad. when they are glowing that means fuel is entering the exhaust, and its almost always a failed coil, or a worn down cap and rotor.
If you have a sc400 with glowing cats you should inspect the caps and rotors, then test the coils unplug and see if there is a difference, if no difference when you unplug the coil then you have a bad coil.

Lokz

iTrader: (1)

Just read dates and its way too old probably a lot of them owners have fixed it all long before. But i'm still going to let all this stay here so other people can read.

You all can also buy a spark tester its like $5-10 and pull your coil out and hook it up to spark tester and see if the coil is working by cranking the car and looking for spark. This is the harder way, also when you guys killed your cat with raw fuel you might as well check if your spark plugs are not fouled it might be needed to be cleaned or replaced. Check oil and smell it see if it smells like fuel too much gas in oil can spin bearings in your motor. Throwing parts at car without checking/ verifying the problem will not fix a lot of you car issues. I might be late but i thought it would be nice to share the info with you all. There is not really a shortcut for doing it right.
Cheers,
-Lokesh

CELICA XX

I know this thread is very old, but I wanted to thank the contributors who pointed me towards the ignition coil.

I just fixed a 93 LS400 running VERY rough with glowing red cats.

Replacing both ignition coils solved the problem. (QYL brand which sold on Amazon for $35 for both coils)

PERRYinLA

Same here - there's many "loss of power" threads on this forum, some reach the right conclusion, others are inconclusive.
But clearly, ignition coils are the first thing to check, and then less likely, but still possible, a bad rotor, distributor cap, or coil wire.
To put it all in one post, if your V8 suddenly has....
- loss of power, rough idle, vibrating engine
- hesitation in the throttle
- change in exhaust tone and bad, gassy/dieseling smell
- rattling/pinging sound coming from the catalytic converter area when gas pedal is tapped
- and yet the check engine light does not go on

...the first thing to check are those two ignition coils!
As mentioned elsewhere, the original coils tend to go on high-mileage cars, especially the driver's side one (because of the high heat). Mine went after 175K miles (and 30 years!).
After 30 years the plastic locking tab in the connector also broke, but putting a layer or two of electrical tape on the coil connector made the connection tight enough, even without the locking tab.

Along with an extra serpentine belt, it's a good thing to carry a spare coil in your car - even though one failing does not disable the car, you don't want to drive far with a failed coil - you could ruin the catalytic converter!
The OEM coils cost ~$70+, but if you don't need overnight delivery, you can get a generic equivalent for less than $20 online.