95 355 SLOW DOWN 1-4 Light

Purchase a cheap laser thermometer (~~ $20 @ Harbor Freight) to see if the right side cat is over 700 degrees.

An extremely overheated cat (in danger of catching the car on fire) can glow a dim red in the dark.

 

Either your cats are WAY too hot because of something messed up upstream (less likely), or your cat ECU's are cracked and failing (more likely).

http://www.ricambiamerica.com/product_info.php?products_id=208023

 

I had the same problem on my '95 F355. It was intermittant, and caused by corrosion in a connector.

Eventually the light would come on and stay on. Cat ECUs were replaced under the 8 year emissions warranty on my car, along with a lot of other emissions related items like the cats themselves.

 

It's just two bolts to swap each exhaust ECU. If the SLOW DOWN light switches sides, that usually means a faulty exhaust ecu.

...but, don't do that test if a cat is glowing red. A glowing cat is a real problem...a bad exhaust ecu is not.

 

I got a slow down light yesterday too, but it was my own doing (fairly sure). Messing with my exhaust valve it seemed like it wasn't opening, so I wired it open to see what it should sound like. Since I was expecting to be tinkering a bit I didn't put the heat shield back on so I could get to it. So last night it came on when driving slow in stop and go traffic; once I got some speed it went off. Put the shield back on, didn't come back on today. I'm thinking the inlet air temp tripped it...

Today was fine, with outside temps around 87F. And I just can't bear to take that wire off the valve, it sounds too good!

 

I had that slow down light thing going off in my 348.
It would flash, stay on, go off, shut down a bank of cylinders, etc.
made no sense when it did it. just random, intermitant crap.
turned out to be the exhaust ecu.
found it be swaping sides.
new one from ricambi fixed the problem.

Oh, the old one had a black epoxy on it, the new ones have
green. the one that failed was black. it had separated from the
plastic. the first time it failed was after the car was in heavy rain.

 

Bingo.

 

Be careful with that.... If wired open the cats never get full flow of exhaust gas during closed loop operation and same for the O2 sensors. Result is that the engine will run rich. Very rich. Potentially this can cause damage to the cylinder liners via washdown.

 

I'd suggest treating it as a real problem with overtemp, since that cat ecu is there to help prevent you from being burned alive in your car.

Did you spend $20 for a laser thermometer? Shoot the laser at the right side cat. If it's cold, then you can play around with ecu connections, new exhaust ecus, etc.

But if the cat is getting raw fuel dumped into it to heat it up wildly, then you are treading at the very edge of where driving turns from safety into a nightmare.

 

Thanks David, never saw that reasoning before in my searches. Good enough for me, no sound is worth any risk of engine damage.