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Thread: 355 slow down light

  1. #1
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    Default 355 slow down light

    Anyone care to offer an opinion on a strange fault I had at the weekend. (1999 car)
    Car not been out for 3-4 weeks so thought best take it out for a quick 10-20 mile trip to keep things in order.

    About 2 miles from home coming up a slight hill I suddenly lost all power, almost coasting it was still running but totally gutless. Thought it might have been out of fuel for a second but I had just put about 30L in.

    I dropped into neutral and pulled over, tried to rev a little but did not want to rev. Turned off and waited a minute and then turned on again and running fine.

    200 yards from home the slow down light came on for about 5 seconds then went off. As I came to a stop at a junction just before my street it lost all power again but then came back about 3 seconds later. Drove the rest of the way home ok.

    I looked over the leads and everything looks ok. I guess could be coil pack? If it dropped an entire bank would it cause this issue? It was not just dropping a cylinder as I have had that before and coil packs were replaced about 2 years ago. How long do they last? It gets rather hot in there!

    Cheers!

  2. #2
    A348W's Avatar
    A348W is offline I have a dodgy moustache - the Ferrari 308 Club Member
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    Sounds like it could be exhaust temp sensors / ecus.

    A few threads on fchat about this.

    I currently have a similar intermittent problem on my 348. Disconnected the exhaust ecus and now no problems, I donít have cats so donít need to worry about cooking them. Iím just trouble shooting at the moment to see if I can fix it. I think the 355 is similar ish!

    Iím sure that know more will be along in a bit.

  3. #3
    F355GTS's Avatar
    F355GTS is offline Shocking waste of good kevlar - The Ferrari Enzo Club Member
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    Default

    I don't think the Exhaust ECU's will cut all power least not until it get's really bad and the slowdown light would be on or flashing

    I'd look to fuel supply, sounds like the engine is being starved then running lean hence the slow down light.

    I think (might be wrong) that a '99 car has one fuel pump whereas earlier cars have two.

    ps I still have the spare coils if you want to borrow them again

  4. #4
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    Nice one mark. The car had new plugs in March so I think I can rule those out.
    Fuel pump, very possible I guess its probably the factory item. Don't suppose there is any way of logging fuel pressure?
    Coil packs, also possible.

    I have never had SDL on before and had only been driving quite gentle so doubt it was a "true" reading IYSWIM.

    Will try and get out one night this week and see how it goes.

  5. #5
    ronrob's Avatar
    ronrob is offline Rear lights like a farm gate - The Ferrari 348 Club Member
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    As Adrian said, take the time to read all about CAT ecu failures on Fchat. There was talk about improvements to the design of these small, potted modules, but they still fail often. Could be due to something else, but you have classic symptoms of CAT ecu failure when the the main system shuts down the bank where it thinks that the CAT is overheating (safety measure). Since there are separate ECU's for each side, if you can identify which side is shutting down, you swap the ECU's over to see if the other side shuts down. There are hundreds of posts on the subject.

  6. #6
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    Sounds like possible cat ECU or thermocouple.

  7. #7
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    Carper Mike
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    Quote Originally Posted by Pangea View Post
    Sounds like possible cat ECU or thermocouple.
    +1

    Classic symptom of ECU throwing a (probably) false alarm.

    I had exactly the same end of 2016 in my 355. The bill was £ 373 made up as follows :-

    "Investigate, diagnose & fit 1 x R/H CAT ECU = £ 150 + VAT"
    "Exhaust heat probe ECU p/n 179278 = £ 161 + VAT"

    So not too painful at all .... not had the problem return since ... yet !

    I know some / many 355's run with the ECU's disconnected and the SDL bulb removed from the dash due to the repetitiveness of this false fault showing up.

  8. #8
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    Regular issue on 355ís

    The ecuís get very hot. They crack on top. Water gets in. ďSlow downĒ light comes on and you lose a bank.

    Had it on both sides of mine. Changed the bits myself, very easy job!

  9. #9
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    Have to say, it does not sound like a cat temp ECU to me, nor an issue with the cats or thermocouples. If the cat temp monitoring system triggered the loss of a bank, whether by sensing a genuine overheating cat, or through a fault in one of the ECUs or thermocouples, the power loss associated with a dropped bank would be accompanied by a flashing Slow Down light (assuming the bulb(s) are in the dash, which they seem to be).

    I have had a bad cat ECU on my car, so I know the fault well. In my case, a couple of days in the airing cupboard followed by siliconing up the cracks in the potting resolved it. But I think this is something else.

  10. #10
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    My thoughts would be something common to both banks such as petrol supply.
    Even with a SDL on and the ecu dropping a bank, the engine would still have some power and would rev on 4 cylinders, just sound rough.

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