512 TR hot start problem, not white wire related | FerrariChat
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512 TR hot start problem, not white wire related

Discussion in 'Boxers/TR/M' started by mmorgan, Jun 8, 2022.

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  1. mmorgan

    mmorgan Rookie

    Dec 16, 2003
    46
    San Diego CA
    Full Name:
    Michael Morgan
    #1 mmorgan, Jun 8, 2022
    I have a 1994 512 TR.

    I installed the white wire bypass solution and now my car starts up when cold every single time, problem fixed.

    But now, after the engine warms up fully, it will not start up again when hot. The starter motor spins the engine just fine, just will not fire up. When the engine is hot, the car runs perfect, good idle,etc. After the hot car sits for an hour or so, the engine will start reluctantly with a very loopy idle, oscillating between 1000 and 2000 rpm or so. After a complete cool down, it is back to starting and running/idleing just perfect.

    It is just the hot start that is the issue. I can try to put my timing light on the spark plug wires and see if I have spark. Could it be a flaky crankshaft position sensor? Can I get error codes from self diagnosis buttons/LED's ?

    Fuel injection system is Motronic M2.7. I am hoping maybe Steve has some answers....
     
  2. flash32

    flash32 F1 Veteran

    Aug 22, 2008
    6,897
    Central NJ
    Full Name:
    Dominick
    #2 flash32, Jun 8, 2022
    Could be the fuel regulators ..common issue with hot start issues in the 512tr .. mine were changed when had hard hot start problems ....mine was hard not a no start condition so maybe not

    Sent from my moto g power using Tapatalk
     
  3. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,779
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #3 Steve Magnusson, Jun 8, 2022
    Well, the starter motor always correctly spinning the engine when cold or warm is a bit of a victory ;).

    Unfortunately, Motronic isn't so easy to debug as everything is mixed together in one giant ECU for each bank doing everything, and it's a very "smart" ECU, I believe, which decides whether it's happy, or unhappy, before doing the next events (and I'm unsure if, that if one ECU is unhappy, it communicates its unhappiness to the other ECU so even the "good" bank won't run -- i.e., it intentionally won't run on a single bank). I think it would certainly be OK to try to read the flashing light error codes, but some may get "lost" after some correct running (i.e., maybe the best time to do it would be immediately after some no restart warm cranking). I do think that your issue sounds more like some missing/bad input signal to the Motronic ECUs is causing Motronic unhappiness (so it intentionally does nothing), but you could try using a spark tester, or timing light, to see if you have ignition present during cranking (but no spark may be the Motronic ECUs intentionally not creating spark for some other reason). The waveforms for the RPM and cam (phase) sensors are shown on page C74 of the 512TR WSM and at the start of Chapter C, but I have no special information beyond what's in Chapter C of the 512TR WSM (but, without the specialized F tester, confirming/denying the RPM and cam sensor waveforms during the no start warm cranking is where I'd begin the diagnosis). Good Hunting!
     
  4. mmorgan

    mmorgan Rookie

    Dec 16, 2003
    46
    San Diego CA
    Full Name:
    Michael Morgan
    #4 mmorgan, Jun 8, 2022
    Thanks Steve!

    I forgot I had the workshop manual, I will take a look. I read about the Motronic M2.7 used in some other cars and indeed it is quite complex, many input sensors going into the control module. At the end of the day I believe I will be taking it to the dealer. I have fixed most of my issues with this car in the past by myself, probably not this one though. Being a retired electronic engineer, my earlier electrical issues were fairly easy to fix, once I figured out the car's bloody schematic and figured out where the connectors were, etc.

    Unfortunately my oscilloscope is not a storage scope, may have to drag my wife into helping me troubleshoot if I decide to dig deeper. Steve, can you read the WSM OK? I am using an old version of acrobat for some strange reason and the printing is pretty broken up.
     
  5. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,779
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #5 Steve Magnusson, Jun 8, 2022
    Last edited: Jun 8, 2022
    A-frickin'-men! The 512TR schematics are, literally, terrible and painful to use! My 512TR WSM pdf copy was/is also missing page L31 with the item descriptions (I got a copy of page L31 from Mel, but it's too big to upload).

    My pdf copy seems to read OK on the screen (but I've never tried printing any it).
     

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