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Thread: Intermittant shudder on 1990 3.9L RRC?

  1. 20th December 2009, 01:54 PM #1
    CSK
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    Intermittant shudder on 1990 3.9L RRC?

    Hi,

    Last week I had my alternator upgraded from 50A to 108A Bosch unit. Yesterday I did a 450KM trip in it all went well except for a occasional shudder, it felt like the engine was cutting out. It happened everytime I accelerated for a while and once while at 100km/hr then stopped doing it.

    Any ideas as to what this could be? ECU on it's way out? an alternator related problem?


    Cheers.
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  2. 20th December 2009, 02:09 PM #2
    PhilipA
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    Well , the 85 amp Bosch alternator often causes a problem with 3.9 s by causing interference in the signal from the amplifier to the coil and apparently then to the ECU. So probably applies to the bigger one.

    The fix is to reroute the signal lead from the dizzy to the coil well away from the alternator eg down the LH head to the firewall then down the guard. Alternatively you could try to replace the wire with a shielded wire with the shielding earthed at both ends.
    The major symptom is that teh engine misses at about 3000RPM and becomes worse with high electrical load eg headlights on.
    Regards Philip A
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  3. 20th December 2009, 02:34 PM #3
    CSK
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    Thanks for the prompt response Philp. If this problem isn't fixed immediatly will I be causing damage to the ECU?
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  4. 20th December 2009, 03:32 PM #4
    PhilipA
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    I do not know, But I think some in the past had the problem for a long time before they tried the fix with no long term ill effects.
    Regards Philip A
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