Hi guys, so after a year ownership of my 355, finally I also experienced the SDL problem. Today I have taken my car from the workshop after a clutch replacement and on the way home, when the engine has reached its working temperature, the Slow Down 5-8 light has started to blink and maybe a minute after that it stayed. The car lost 4 cylinders for several seconds, then they have fired up again... actually the bank of cylinders has stopped and started again about 100 times untill I got home. For that time the light has dissapeared and showed also 100 times... Now I don't believe in coincidences and I think that's related to the clutch replacement and to the exhaust removal in particular. It doesn't act like the cat is really the problem. The guys in the workshop said, that they have only removed the muffler and they haven't touched the cats, but as far as I know, there is a termocouple on the muffler too and maybe the problem is somewhere in that direction. Unfortunately until I got home it was already dark, so the only thing that I have saw is that the little black hose has not been attached to the exhaust valve. My question actually is if it is possible that the SD 5-8 light will blink if the exhaust termocouple is not working?
Also, who knows what they bumped into or touched while they were in there. Stuff happens. You should check any and all electrical fittings for insurance. Check the bypass stuff too. It would be easy for them to forget to reattach something.
The behaviour you describe does sound like an actual cat overheat situation - cat heats up, fuel is cut, cat cools down, fuelling is restored, repeat. If it was a failure of the thermocouple or one of the cat ECUs, I wouldn't expect such a cyclical pattern. Still, it's trivial to swap over the thermocouple and cat ECUs and see if your problem moves to the other bank. Is the car running OK? I had exactly the same behaviour when an ignition coil packed up and sent lots of unburnt fuel through the cat, which overheated and caused the slow down light to (correctly) light up. Funnily enough, this also happened right after I'd had the car serviced but was unrelated.
Out of curiosity, what is your coolant temperature when the car has been running for a while? It should be in the 90°C range. If it is running too cool, 80°C and below, the engine management will keep the fuel mapping in secondary enrichment, adding extra fuel. So check your coolant temperature the next time you are driving it, and especially if you get another slow down light. The other thing that you can do is buy an inexpensive pyrometer and check the temperature of the catalytic converters, and headers, to see if they are overly hot. This would also indicate a rich condition. If the temperatures come back okay, they you may want to try swapping the thermocouples from side to side, and see if the problem jumps banks, from 5/8 to 1/4.
Well nothing wrong with the cats actually. They are new, by the way (aftermarket ones). Today I have switched the thermocouple computers to see if the problem is not there. But before installing them, I have cleaned all the connectors with contact spray and then I have pushed them good in their places. Then I've placed the little black hose on the exhaust valve where it belongs and taken the car for a drive. And then - OH, MIRACLE! No slow down light at all. I have tortured the car in traffic jams for about an hour, then I have taken her out of the city for a speedy drive and I have actually been out for 3 hours - no lights at all. So maybe some of the connectors was not pushed hard enough after reassemble... Because it just made no sence - yesterday at the traffic lights car switched and cut the bank several times on a 20 sec. idle... So for now the problem is solved and I really hope it will be for long... Ernie - about the water temperature - in town it stays stable on 90°C, but on the highway with more than 200 km/h, it can never go more than 70°C-75°C. Is that normal?
No. It should stay in the 90°C range, even on the highway, maybe dipping down to the 82-85°C area, but not all the way down the 70-75°C that is way too cool. I suggest you put in a new 82°C thermostat. Have a read of this thread http://www.ferrarichat.com/forum/348-355/377706-355-owners-only-more-data-samples-needed-anonymous-poll.html
Thanks, I already have that in my list. First I wanted to buy an OEM one from Eurospares, but I have read somewhere in the forum, that this here: WAHLER 4255.92D THERMOSTAT INKL.DICHTUNG OPEL | eBay is a perfect replacement and it will do the same job. Not sure how correct that info is though...
My slow down light has been coming on intermittenly.. It was diagnosed as the Cat temp ECU.. Left side rear of the car, there are two ECUs.. The one that is horiztonal is the Cat Temp ECU, and is literally two plugs and two bolts.. I bought one and swapped it myself (i am NOT mechanically inclined) in probably 90 mins.. Be sure to go up front to the hood and shut off the battery/electical system using the black dial. *The electrical system shut off knob is also a fix that worked for me for a few months.. Or just dropping it into neutrial (if underway) allow revs to bottom out then slip it back into gear. Hope that helps some
I had the same issue on my 355, turned out to be the Temp ECU. The ones with the black potting material seem to be the ones I've seen/had go bad. The green ones seem to last the longest. When they start to go bad they get intermittent, they are also kind of pricey.
