348 1-4/5-8 light on how to tell if it is serious or bad ECU?

Well what the exhaust ecu does is monitor the temperature of the cats. I think if the temperature of the cat gets about 1200 deg F it will shut the bank down so that the cats don't get ruined. I had the experiance of one bank getting shut down. The slow down 1/4 was comming on and off from time to time. Then one day the car lost power big time and you could hear a distinct difference in the exhaust note. What I did to see if is what the ecu or indeed the cat was switch the ecu from one side to the other. Sure enough I was getting the problem now on the 5/8 side. So I just leave it unplugged. . Another thing that is common is the termo couplers have a tendancy to go bad. But I would check the ecu's first. Search the archives, there is loads and loads of info about this subject.

 

would removing the cats help this at all?

 

Uhhhhhh Yeaaaah if there are no cats they can't get hot. But why go to the trouble of removing the cats, unless you don't want them. People have taken the cats off but that is more for performance gain. Even if you did take the cats off you still could have a retarted ecu like I did. My exhaust ecu was so bad that even after the car had been sitting over night when I turned it on the light came on.

 

The thermocouple ECUs are located on the shock tower. One on each side. Follow the lead from the thermocouple (braided stainless wire, 10mm nut attachment) in the catalytic converter, it will lead you to their location. Two connectors, one to the wiring harness and then ultimately to the Motronic, the other connects to the thermocouple.

Highly recommend seaching the archives on this topic, much more information including photos, troubleshooting, costs, and how to know if you have the latest generation thermo ECU.

One last note: The quickest way to know if the Slow Down is genuine is to look at the catalytic converters. It'll be glowing. Otherwise, it's an electrical gremlin.

Best regards,

Rob Schermerhorn