Slow Down Light

THANKS FOR EVERYONES HELP SO FAR. I HAVE A 1999 550 THAT MY UNCLE LEFT TO ME WHEN HE PASSED AWAY. THE 30,000MI CHECK WAS COMPLETED ABOUT 6 MONTHS AGO. RETURNING FROM DINNER I SUDDENLY RECEIVED A SLOW DOWN ON THE MULTI FUNCTION DISPLAY. MY FIRST THOUGHT WAS WOW HOW DID THE LOCAL POLICE MANAGE TO DO THAT. AFTER STOPPING AND LOOKING IN THE OWNERS MANUEL I REALIZED THAT IT WAS ENZO NOT THE COPS THAT DID IT. LOOKS LIKE THIS IS RELATED TO THE EMISSIONS CONTROL SYSTEM. ANY THOUGHTS ON WHERE TO START, CANNISTERS, VACUUM LINES, CHECK VALVE ETC?

THANKS FOR YOUR HELP
JOHN BENNETT

 

I experienced the same problem with my 04 this summer. After running for approximately an hour at 90 mph the message kicked in and fuel flow was automatically reduced. I pulled over and waited a few minutes and was back on my way. I called FNA the following day and was advised that it is related to the temp of the cats. The problem has only surfaced once again two months later. MY car has a tubi with 19k on the odo. No troubles since.

 

My 456 experienced the same thing. The trouble turned out to be the computers that interpret the temp signals from the cats. There are two, one per bank. These are apparently a trouble spot on 456s, perhaps the 550 suffers the same malady? Anyway, I (eventually) replaced both computers, and this solved the problem. Price on the computers runs about $300 each.

 

Thanks for your responses. I thought about what I had changed prior to encountering this light. I added a bottle of NOS injection cleaner to the fuel system. I filled the tank up the rest of the way and decided to run it as much as possible to put more fuel thru the system. Light went out.