90 mph highway was pull/slow down light | FerrariChat

90 mph highway was pull/slow down light

Discussion in '308/328' started by Austin Newman, Jan 19, 2020.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, Skimlinks, and others.

  1. Austin Newman

    Austin Newman Karting

    Dec 18, 2019
    229
    Memphis
    Full Name:
    Austin Newman
    #1 Austin Newman, Jan 19, 2020
    Last edited: Jan 19, 2020
    From what i gather this light indicates high CAT temps and i should back off? If so, what causes it to run hot, and how do i fix? 100% stock build


    Sent from my iPhone using FerrariChat.com mobile app
     
  2. 4right

    4right F1 Rookie
    Rossa Subscribed

    It’s caused by unburned fuel in the cats, you have either an ignition or carburation issue. The unburned fuel ignites in the cats causing them to overheat.
     
  3. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,040
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    Unburnt fuel+air mixture entering the exhaust stream and combusting inside the cat -- if real, can be caused by a cylinder, or a whole bank, losing ignition spark. Also if real, the cat would be glowing red hot so best to pull over and have a look in the cat exit area for glowing/smoking. The ECU running this warning light is often flaky so things like the slowdown light coming on immediately after cold start-up or the self-test not working correctly are signs that it is bad. Also, the thermocouple losing continuity (a bad connection to the ECU) will turn the light "on".
     
  4. Austin Newman

    Austin Newman Karting

    Dec 18, 2019
    229
    Memphis
    Full Name:
    Austin Newman
    If real... what is a remedy? Driving around down all day no issue.. get on the highway and give it the mustard at 90 and it throws a light... backed off and it stopped..


    Sent from my iPhone using FerrariChat.com mobile app
     
  5. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,040
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    What does "throws a light" mean? Does it just go from "off" to "on" solid? It really shouldn't as it should flash for a while before it stays "on" solid -- see your OM for a description of how the system operates.

    How is your self-test working? Always perfect at initial start-up? No light at all at initial start-up doesn't look bad, but is really a failure.

    The first thing to do is determine if it is correctly detecting a real overheating condition, or if the ECU is just giving a false signal.
     
  6. Austin Newman

    Austin Newman Karting

    Dec 18, 2019
    229
    Memphis
    Full Name:
    Austin Newman
    I was driving down the highway doing about 90 and i saw it flick on and off.... then i got back on the throttle again and it flicked on and off again. I have not seen a steady light at all. I don’t believe the light comes on during initial startup/warm up


    Sent from my iPhone using FerrariChat.com mobile app
     
  7. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,040
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #7 Steve Magnusson, Jan 19, 2020
    Last edited: Jan 19, 2020
    Both of those behaviors are more consistent with a bad warning light ECU (rather than an actual overheating condition). See page 78 of your 308/84 OM for a description of the system operation, and page 21, item 9 for a description of the self-test -- every time you turn the key "on", the slowdown warning light should light up for a second, or two, and then go out. If the warning light just stays always "off" after turning the key "on" = bad ECU for the self-test function, and that gives no confidence that the ECU's temperature sensing function is working correctly.
     
  8. Austin Newman

    Austin Newman Karting

    Dec 18, 2019
    229
    Memphis
    Full Name:
    Austin Newman
    I stand corrected.. I don't recall seeing the self test indicate however, upon actually checking and looking for it doesn't in fact light up when the aux power it turned on and then stayed on for a second before shutting off. Well let me ask this.. if I removed the CAT and put in a test pipe instead.. I assume this issue would be null as there are no cats to get too hot, correct?
     
  9. Austin Newman

    Austin Newman Karting

    Dec 18, 2019
    229
    Memphis
    Full Name:
    Austin Newman
    Also,

    If the cats were actually getting too hot due to unburnt fuel passing through What would be your first go to issue to correct? Spark plugs, coils?
     
  10. mike996

    mike996 F1 Veteran

    Jun 14, 2008
    6,685
    Full Name:
    Mike 996
    The slow down light system is notorious for failing and there is no replacement for the control unit. Several people here in the past have claimed it would be easy to make a replacement unit, claimed they were going to make one and have all failed to actually do it. ;)

    Since your system is not doing a proper self check, it is clearly not working. Mine started illuminating at random on my first long trip in my 328 - across country two days after I bought it. Scared me the first time but after a quick check, I decided there was no actual overheating issue and I continued to drive normally. When I got home and did some more research, I removed the cat and installed a straight pipe. It still lit up at random on occasion so I electrically disconnected the system completely.

    TBH, I would prefer the Cat to be in place and the system operating correctly but since there is no replacement for the control unit, that's not an option for me. I don't want the Cat there without the system. In one sense the whole thing seems odd...I'm not aware of any other car that has a system warning about a Cat overheating. I ASSUME it has to do with the placement of the cat where an engine oil or fuel leak could be ignited by an overheated cat. But I'm just guessing re that.

    The most likely cause for a slow down light to appear in a properly operating system is an ignition failure of some sort. Could be any of the "usual" suspects when ignition problems occur, secondary wires, plugs, coils, crank triggers, etc.
     
  11. Austin Newman

    Austin Newman Karting

    Dec 18, 2019
    229
    Memphis
    Full Name:
    Austin Newman
    [QUOTE="
    In one sense the whole thing seems odd...I'm not aware of any other car that has a system warning about a Cat overheating. I ASSUME it has to do with the placement of the cat where an engine oil or fuel leak could be ignited by an overheated cat. But I'm just guessing re that..[/QUOTE]

    I thought the same thing.. Like this car is notorious for a failing system that I have never known another car to have and seems just a headache.. to your point. I guess it is a weird way to indicate misfiring. But in my driving at idling, low speed, city driver, and high speed highway pulls I have not noticed any indication of that. Also it was approx. 40 degrees when driving.. not 90 so getting to hot is a stretch too. I may just remove the cat and put it on the shelf to say I have the OEM part but place a test pipe for sound, power and no worries of burning up the cats...
     
    EastMemphis likes this.
  12. moysiuan

    moysiuan F1 Rookie
    Silver Subscribed

    Nov 1, 2005
    3,628
    Canada
    Remove the thermocouple and clean it with a brass wire brush and then some alcohol. Then clean the contact where the thermocouple connects to the control unit, ideally put on some Deoxit to ensure a good electrical contact. Sounds like a minor intermittent connection.
     
  13. mike996

    mike996 F1 Veteran

    Jun 14, 2008
    6,685
    Full Name:
    Mike 996
    Certainly a good idea to clean the thermocouple/connections as described!. Just don't have overly high expectations! ;) I was having random lights even with the straight pipe and the thermocouple connected but wire-tied out of the way in open air. I continued getting them with the T-couple completely disconnected! :(
     
    Austin Newman likes this.
  14. Austin Newman

    Austin Newman Karting

    Dec 18, 2019
    229
    Memphis
    Full Name:
    Austin Newman
    any downsides to running the test pipe?
     
  15. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,040
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #15 Steve Magnusson, Jan 20, 2020
    Last edited: Jan 20, 2020
    Yes, with no hot heat source in the exhaust stream, unburnt fuel+air just passes out the exhaust pipe without igniting. However, as Brian said, this is really no solution to unburnt fuel+air going out the exhaust pipe.

    Verify the ignition system is all OK, and check that the A/F mixture is set correctly (which would include checking that the WUR is working correctly).
     
  16. Rifledriver

    Rifledriver Three Time F1 World Champ

    Apr 29, 2004
    33,736
    Austin TX
    Full Name:
    Brian Crall
    Not from a functional stand point. 2 things to consider.
    1. New cat temp control units are available for the late 328, they are expensive. The late version can be used in early cars with some minor wire connection changes.
    2. If there is any validity to the warning light there is an issue potentially robbing the car of power and preventing proper running. That should be determined no matter how you choose to deal with the situation.
     
    Natkingcolebasket69 likes this.
  17. Lawrence Coppari

    Lawrence Coppari Formula 3

    Apr 29, 2002
    2,149
    Kingsport, TN
    Full Name:
    Lawrence A. Coppari
    Quite some time ago my '87 GTS was warning me occasionally with the slow down light illuminating while driving. I replaced the O2 sensor. The problem went away and never returned (knock on wood). However, I must add that my system always (and still does) remains illuminated for a second or two when I first start the engine.
     
  18. Austin Newman

    Austin Newman Karting

    Dec 18, 2019
    229
    Memphis
    Full Name:
    Austin Newman
    how do I check the fuel/air mixture?
     
  19. kcabpilot

    kcabpilot Formula 3

    Apr 17, 2014
    1,527
    California SF bay area
    Full Name:
    Paul
    From what I've read here this seems like it may be legit. Seems as though it's predictable and repeatable - go 90 mph and the light comes on, back off or "Slow Down" as the warning indicates and it stops. To read the A/F ratio at home you need something like the Innovate Motorsports wide band kit, they're like $300-$400. There are some cheaper brands out nowadays but I don't know how well they work. Or you could just take it to a shop and have them check it.

    I guess the first thing to do is just a thorough visual check, make sure all the little hoses and connections are good and nothing is hanging loose. After that it's a matter of troubleshooting to find the culprit. Different people have different methods depending on how stuffed your wallet is. Patience and methodical thought can save you a lot of money at this point. If you have to pull out the shotgun and start shooting from the hip at least shoot the cheap stuff first. You might get lucky.
     
  20. EastMemphis

    EastMemphis Formula 3
    Owner Silver Subscribed

    May 25, 2019
    1,719
    Memphis, TN
    Full Name:
    John
    A low tech way of determining if the mixture is running rich is to sniff the exhaust, or place a cloth over the exhaust for a few seconds and sniff that. The nose is a great detector of unburned hydrocarbons.
     
  21. kcabpilot

    kcabpilot Formula 3

    Apr 17, 2014
    1,527
    California SF bay area
    Full Name:
    Paul
    True but not at 90 mph!
     
    EastMemphis likes this.
  22. Rifledriver

    Rifledriver Three Time F1 World Champ

    Apr 29, 2004
    33,736
    Austin TX
    Full Name:
    Brian Crall
    Air fuel ratio does not cause cats to overheat, unburned hydrocarbons do and many things cause that. Of all the cars I see that have a cat overheat problem the fuel mixture is almost never the cause.
     
  23. Rifledriver

    Rifledriver Three Time F1 World Champ

    Apr 29, 2004
    33,736
    Austin TX
    Full Name:
    Brian Crall
    You really need to have it read by a 4 gas analyzer to know much. The ratios of the gasses tell you a great deal. In fact if in tuning an engine and I could only read one gas it would be CO2, not CO.
     
  24. johnk...

    johnk... F1 World Champ
    Owner

    Jun 11, 2004
    10,629
    CT
    Full Name:
    John Kreskovsky
    And that would be because? (rhetorical question.)

    Image Unavailable, Please Login
     
  25. Rifledriver

    Rifledriver Three Time F1 World Champ

    Apr 29, 2004
    33,736
    Austin TX
    Full Name:
    Brian Crall
    #25 Rifledriver, Jan 20, 2020
    Last edited: Jan 20, 2020
    That chart is great for an engine with no running issues. Introduce a problem outside of simple wrong mixture and the ratios no longer follow what happens when mixture is set outside of correct.

    CO2 is the one gas on its own is a good indicator of combustion efficiency. CO can be set perfect but if ign or cam timing is off or if it has a ring issue it will still run lousy. HC can be adjusted too but if any other factor is bad it will still run like crap. O2...same thing. With the twist of a screw I can make HC, CO or O2 anything I want. Not CO2. If you get good CO2 you have good combustion efficiency. Only way to get it.
     

Share This Page