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Motronic ECU error code

Discussion in 'Technical Q&A' started by JIMBO, Apr 27, 2020.

  1. JIMBO

    JIMBO Formula 3
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    Oct 31, 2003
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    Jim DeRespino
    OK, new problem. Yesterday I had the car out for about 20 minutes of active driving for the first time since starting the major 7 months ago. I took the motor up to 6500 RPM and kept revs around 3000. The car performed well, no smokes, no leaks. It was idling a bit low at 5000 but smooth.
    Today I vacuumed out the AC system, and while charging, after about 10-15 minutes the car stalled. With the AC on, the idle picked up to 1000, the vent temp came down to 60, the ac condensor and radiator fans came on as they should and all seemed well until it died. No fuel, no spark. I guess the ECU's did not like something?
    Checked all fuses - OK
    Unplugged and replugged all connectors on the relay board - NADA
    I checked the Motronic diagnostic and I got the usual code for the "catalyzer" on the 7-12 bank, and then just rapid, steady short flashes with no pause. On the 1-6 bank I got the catalyzer code and then the RPM sensor code and then no more codes.
    I unplugged and replugged the RPM sensors - no change.
    I also noticed that the cabin AC fan was not working.
    Any ideas on where to go next? I will check for 12 v on ECU pin 27 tomorrow.
     
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  3. EastMemphis

    EastMemphis Formula Junior
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    This may be totally wrong and I don't even know what car you have, but I would hazard a guess that idling for 10-15 minutes with the A/C running ran down your battery enough to cause the voltage to get in the crazy range for the ECU. How old is your battery? How long had it sat without being used before this test?
     
  4. Qavion

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  5. JIMBO

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    Battery is a few years old but was fully charged before driving car two days ago. It still spins the motor rapidly.
     
  6. JIMBO

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    OK, problem solved.
    I was on the phone talking to Tim Fulmer and something clicked. The car stalled just after the radiator cooling fans kicked in. Also running were the ac condensor fans, the ac cabin blower and the fuel pumps. These are the exact circuits taken out of the fuse box in the Dave Helms conversion and all have a separate, common power lead from the battery. Tracing the power lead from the battery led me to an electrical junction block that I had installed. I very scientifically jiggled the wires and tried to start the car again and she roared to life (and NO CEL's) ! Upon closer inspection the set screw on one side of the junction was loose and I was able to pull both the red and white wires out with minimal tension. It was actually pretty lucky that this happened with the car in the garage rather than on a long cruise. Should I have tinned the ends of the large wires before putting them in the junction?
    How would a real automotive electrical professional join all 3 wires together? A large crimp connector? I don't want this to ever happen again. I initially spliced in the junction to bring 12V to the white wire.
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  8. RedNeck

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    Remembering back to my IPC Certification classes, you do NOT tin the ends of the stranded wires prior to inserting them in any kind of junction of that nature, nor should they be twisted. Sounds like it may not have been tight enough to begin with if it backed out, or it was a cheap block that failed.
     
  9. Steve Magnusson

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    #7 Steve Magnusson, Apr 29, 2020
    Last edited: Apr 29, 2020
    The trouble with a large, high-quality crimp terminal is the tool to do the crimping might be $500+. Running those rather small screws into such a large bundle of fine strands won't clamp very well (looks like most of the strands just got pushed to the sides). If you're going to use a screw clamp, you really need something between the clamp screw end and the wire strands (to gather the strands together and put the clamp load onto all of the strands) -- something like this style IMO:
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    (Would've been a lot better to not cut that wire and add a terminal to the existing male stud on the positive battery terminal -- JMO.)
     
  10. flash32

    flash32 Formula 3

    Aug 22, 2008
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    Wouldn't you be better off using a piece that has the same amount of "holes" as leads .. so not to double tap one screw just like on a electric panel in home

    Sent from my moto g(7) using Tapatalk
     
  11. JIMBO

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    You won't get any argument from me. In retrospect, I have no idea why I cut that wire in the first place. Maybe I will look into just running a new wire to the battery cable. I have to look at the other end and see how that mates to the Dave Helms conversion.
     
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  13. JIMBO

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    That makes sense, too flash. I have this three hole terminal block in my box of electrical components, but the set scerws will still tend to just push the wires to the side. Surely someone makes the correct junction for this type of application.
     
  14. JIMBO

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    Another suggestion by Tim Fulmer would be to crimp two large ring terminals on the ends of the 8 gauge wire and then connect those via some junction block with studs and nuts (similar to the 512TR engine junction of the battery cable, alternator and starter wires. But where do you find such a thing? And remember it has to have a cover because the whole metal part is hot (12V).
     
  15. JIMBO

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  16. EastMemphis

    EastMemphis Formula Junior
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    The reason you don't solder stranded wire, especially in a vibration rich environment is that the vibrational stresses will cause the small strands to break, eventually setting the connection to a situation where the wire can break or can be subject to excessive amperage which can cause overheating. So just crimp the wire and leave it at that.
     

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