F355 Slow Down 5-8 Blinking Light and Rattling

I have a '97 355 Spider that had the exhaust failure. I replaced the manifolds with the QV repair and replaced the CATs with Hyperflows. Shortly after the repair, but not right after, On cold start-up after the car had cooled for an hour the slow down light blinked. I headed for the Ferrari Dealer and it went out half way there in cooler weather and I have driven the car trouble free for two months until yesterday after an hour cool down from a 20 mile run I started it in my driveway to put it away and the slow down light started blinking again. It has blinked on each cold start-up since, including an overnight cold soak.

the Cats are brand new, I believe I have some sort of fault. How can I trouble shoot this one?

 

I bought a ECU for the Temp probe and swapped it in all three locations cost with WA sales tax is $280 from FoS - still slow down light is blinking on during cold start up. I checked continuity across the temperature probes each read 1.8 OHMs. I know these are bi-metalic strips that generate milivolt signals when heated but I was looking for something obvious. The only thing I noticed was the OHMS on one of the strips measured 1.3 installed in the CAT but when I removed it it read essentially normal at 1.7 to 1.8 OHM. The others I had measured installed. I ran the car with the temp probe out after I obtain the 1.8 OHM reading with the new ECU and still slow down light flashes. I checked the Air pump fuse and the OXY fuse with no fault found.

Any other comments or ideas?

 

Since you only have 2 cats where is the third ECU location? Or are you saying that with the new ECU you now have three ECUs total and have tried all combinations in the 2 ECU slots?

Do you only have 1 "slow-down" warning light? (that would make debugging more difficult)

 

I thought there were only two also - but there are 3 temp probes and 3 ECUs. There are the two ECUs behind the right Wheel well they service the right CAT and The Bypass valve location Thermocouples and the other ECU and Thermocouple for the left CAT is on the left side under the shock absorber metal cover. I put new batteries in my volt tester and am now reading 2.8 OHMs on the TCs. I have a milivolt meter so I hooked up 1875 watt hair dryer to heat it up and measured 0.28MV when the thing was too hot to touch. It read zero at room temp and -.03 when I touched it to ice, but that wasn't stabilized.

 

Is the thermocouple a resistive element, or is it more complex? If it has other elements at the terminal you will not be able to make an accurate measurements, i.e. caps and/or inductors...

 

All there is seems to be a bi-metallic shielded probe with two wires coming out. Unfortunately I only have one slow down light for feedback. I have just completed a thermal test of all three probes - they all respond very consistently to elevated temperature and climb from 0 to a max at .28 millivolts when I apply my hair dryer. I would say they must have continuity or they couldn't be so consistent. There are no other components to it. I have now swapped the NEW ECU I purchased across all three locations shutting off all power to the car and performing a restart. Upon restart my security system beeps 4 times - very unusual. Then I must push the button again to get the proper two beeps.

Since I have swapped out the NEW ECU twice in each of 3 locations and have 3 consistent T/C readings from room temp to hot, checked fuses for the Air pump and the Oxygen sensor and confirmed the Relay for the Injection Air pump - all with no fault found - I'm totally at a loss for a solution.

Help!!

 

I just checked the 1176/97 OM (page C15), and you actually have 4 catalytic converters (with the two small ones in the exhaust bypass pipes sharing a common thermocouple).

If you unplug one of the ECUs on the main cats does it also "shut down" that sides injection system or automatically turn on the "slow-down" warning light? If not, maybe you could try putting only one ECU in place at a time on one of the main cats and see which ECU(s) give you the erroneous warning light at cold start-up symptom (and confirm that your "new" ECU doesn't) -- just a thought (if it can work that way)...

 

I don't think I have the understanding of what shutting down the injection system does to my engine if done on one side. Wouldn't independently replacing each ECU with my new one discover the problem the same way unless the new one I have is faulty?

 

My 355 does not run the Left T/C lead across the muffler to the lower ECU on the right side. My left T/C lead terminates with a left hand ECU mounted on a left hand frame member near the Oxygen Sensor terminals on the left side. The lower ECU on the right side oriented vertically services the Right hand T/C from the right hand CAT. The Horizontally oriented ECU is NOT properly depicted (It does not service the right hand CAT) and is used for the the bypass T/C on my 355 (the diagram shows the lead going to the Motronic which is false at least for my car).

 

Yes, that OM figure is obviously not quite right, but at least it showed the three thermocouples and four cats

It was more an idea as a way to provide a direct 1:1 testing relationship -- it's a long shot, but what if you had 2 flaky ECUs? (Having a warning light for each ecu is seeming like a much better idea right now.) IME, if you go in and just root around a bit with these type of ecus, the mechanical flexing/vibrating is enough to sometimes seem like a temporary cure.

The thing about unplugging the warning light ecu and the bank shutting down is that (if it did that) you really don't want to run with 4 dead cyl for a long time. Don't know if your 355 is that smart (i.e., can detect the "unpluggedness"), but it's the modern trend (but I'm surprised that you're not reporting a power loss when the false warning light signal does occur because I thought that 355s do detect the same "signal" that turns on the warning light and shuts off the injection system for that bank if present).

Has your self-test been well-behaved at every start?

 

The mode I get is a blinking slow down mode, which doesn't alter the engine operation. In a real problem when the CATs are melting and the system senses it, the light comes on solid bright, and the motronic computer shuts the fuel off to all injectors. The manual implies that the stages of a real failure are that first the slow down light blinks where you are advised to slow down and get to a service center fast and if you don't then it will come on solid and shut you down.

 

Light is solid untill engine starts then starts blinking when engine is running

 

Understood on both counts (sometimes people don't notice when the self-test is completely dead -- and your report matches the OM description).

Have you tried starting it with only 1 of the warning light ECUs plugged in at a time? Don't know if that would give you some other strange fault, but since you're getting an immediate (erroneous) flashing condition if there's an effect you'll know right away.

 

I did as you suggested. I unplugged the left hand ECU, then all three got the same result with the light blinking on each try. Engine runs normally with the light blinking.

 

If you've unplugged all three warning light ecus simultaneously from their main harness connections (not the thermocouple connections), yet the warning light still "flashes" inappropriately, you must have another ecu (or control gizmo) involved in the system somewhere. Any useful OBDII codes or do they just repeat the false indication?

 

I'm taking it to Ferrari of Seattle to have them fix it.

 

After all this fooling around, I made an appointment with the Seattle Ferrari dealer to fix it a week from now. I drove 10 miles to the golf practice range with the slow down light blinking. When I finished hitting the balls about 45 minutes later I started the car to go home and NO blinking slow down light. Drove 10 mi home. No problem. Its hard to fix an intermittent failure.

I think honestly threatening to take the car to the dealer is what fixed it.

 

The blinking "Slow Down 5-8" light has started up again. Looks like we will be off to the Ferrari dealer next Wednesday.

 

Final chapter in this story.... it turned out to be a bad spark plug. The Ferrari dealer replaced it and the problem has disappeared.