91 TR No spark 7-12 | FerrariChat

91 TR No spark 7-12

Discussion in 'Boxers/TR/M' started by JohnMH, Mar 23, 2019.

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  1. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
    1,625
    Dubai / Bologna
    Car ran well yesterday afternoon. Parked it for 10 minutes, then it started on on 6. I limped it a short distance home.

    Checked ignition with timing light. No spark on 7-12.

    Checked igntion cap and rotor, in perfect condition (both were replaced in last 6 months).

    Any dignostic suggestions? Will swap coils left to right next.

    Car is a Swiss spec 91 model, F113B, KE Jet.

    Thanks for any suggestions.
     
  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,035
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    This is a little unusual as the 7-12 coil primary must be working to keep the tachometric relay closed which keeps the fuel pump relays closed. You could have a problem in the 7-12 coil secondary (so no harm in trying the swap) or in the coil wire going from 7-12 coil secondary to the dist rotor -- like the coil wire fell out of the coil ;). Good hunting, and please do let us know your eventual result as your symptom is rare (usually, the 7-12 coil power module pukes, but it won't run on 6 if that happens).
     
    turbo-joe and MOSS like this.
  3. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
    1,625
    Dubai / Bologna
    Thanks, I suspected you might chime in. I will swap modules, coils, wires, and see what I learn. What is a 'coil primary'? So you think the 7-12 ignition module (that sits on top of the coil) may be ok?
     
  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,035
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #4 Steve Magnusson, Mar 23, 2019
    Last edited: Mar 23, 2019
    The coil primary is the winding inside the coil connected to the low voltage wires of the coil that the ignition module sends a switching low voltage high current signal thru (this then causes a high voltage low current signal to occur in the coil secondary winding that fires the spark plugs).

    Yes. The low voltage high current signal that the ignition module sends thru the coil primary is also used as a signal to close the tachometric relay (which closes the fuel pump relays). Since you report that the engine continues to run with no spark in the 7-12 secondary side, that indicates that the signal in the 7-12 primary side is still present (i.e., the 7-12 ignition module is working). Might be possible that enough of a flawed 7-12 primary side signal is still there enough to keep the tachometric relay closed but not sufficient to fire the 7-12 secondary, but this has never been reported yet -- usually, the ignition module works or is just completely dead.

    Since you report that everything inside the 7-12 dist cap looks OKish, I would do two things before doing the coil+ignition module swap:
    1. Just unplug/inspect/replug the 7-12 coil secondary wire at the coil (the wire that goes from the coil to the distributor center terminal).

    If still no joy:
    2. Unplug that wire again at the coil and remove the distributor cap. Measure the resistance from the metal terminal on the end of the unplugged coil wire to the metal terminal holding the carbon button inside the distributor cap = should be something like 800~1K Ohms. If it's a significantly higher resistance = re-pierce the wire at the dist cap end and remeasure.

    If OK and still no joy -- then try the coil+ignition module swap.
     
    turbo-joe likes this.
  5. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
    1,625
    Dubai / Bologna
    Thanks. Sometimes I think the TR's least appreciated feature is its ability to educate.
     
  6. tommydogs

    tommydogs Karting

    Nov 9, 2016
    137
    Los Angeles, CA
    Full Name:
    Tommy Robinson
    I would of course do what Steve suggests first.

    And then inspect the round connectors for each ECU that sit on top of the passenger side rear wheel. Each one has a 9-pin and 24-pin connector. The 9-pin on mine had the smallest hairline fracture that was allowing a wire (or wires) to pull out and "depower" the ECU for the 7-12 bank from time to time, whether the car was moving or just sitting there idling. I would get no fire on that bank, or something silly like firing once a second. I had just had a full engine out service, and then replaced both ignition coils and modules -- this wasn't supposed to happen to me.

    In the end, for good measure, I replaced both round connectors for both ECUs with new units and haven't had a problem since. Plastics are great until they break.
     
    turbo-joe likes this.
  7. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
    1,625
    Dubai / Bologna
    A good point. I know the ring connectors are somewhat worn, it is not beyond the realm of possibility that the fault lies there. Tomorrow I will find the time to investigate.
     
  8. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
    1,625
    Dubai / Bologna
    Update time. The 7-12 coil is bad (intermittent - basically off 90% of the time). HT leads were fine. So now off to find a coil (modules were good). By being equipped with 2 inline 6 engines, the TR is well equipped for effective diagnostic work.

    Thanks to all for the advice.
     
    turbo-joe likes this.
  9. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
    1,625
    Dubai / Bologna
    Alas, that one will not plug directly into my car’s wiring harness. My coil has one large oval wiring plug, not two small twin plugs. I understand Eurospares can provide the oem part. Order sent. Joy.

    What is more strange is the difference in coil between different markets and cat and non-cat cars. Curious as to the reason.
     
  10. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,035
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    I believe that it's just related to the coil primary connector difference that you noted -- and they mangled the description about what version gets what in the 1990 TR SPC (i.e., the 1987 TR SPC shows only 124273 being used on everything so that would be used on early US TR, but my 1991 US TR uses 143413 - but the 1990 TR SPC shows no information for early vs late US TR):
    124273
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    143413:
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