the_zogs

Has anyone had this problem? Could it be the O2 sensors? there are two seperate converters, is there any way to tell which one is bad or both maybe?

I had a muffler guy tell me he could remove the converters and put glass packs in but that would cause a O2 sensor problem wouldn't it? The check engine light would stay on right?

Bronco2

If you take the cats off you will have problem with the SES lite.The way the system works the ECM monitors the O2 sensors before and after the cat. When the cats are cold the ECM will see both before and after cat O2 sensors reading about the same-after the cats warm up the after cat O2 sensor should read "flat" voltage output. This is how the system monitors efficiency. A scan tool to watch the sensor output is probably the best way to see where your problem is. If you can't do this yourself take the truck to a shop-dealer may be your best bet for diagnosis. Then let the muffler guy replace the bad cat. This is a quick and dirty explanation,hope it helps

fletch1024

I own a 98 with 112K, and last week had the following code come up on the SES, "Catalyst System Efficiency Below Threshold (Bank 1)".

After talking to a buddy at the dealership he suggested running a "quality" fuel injector cleaner through the system. He thought it would clear in 3-5 driving cycles. I used a $5 bottle of injector cleaner from autozone, instead of the $.99 cheap stuff and sure enough after about 40 miles the light cleared on it's own.

Don't know if it's a similar issue, but thought I would mention it. Good luck.