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miatawelder

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  2. overheating IC ?

    in Link G1

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    Problem : car (1994 Miata with 1999 engine with aftermarket turbo) runs fine on city streets and freeway (location Texas USA) .  On hard race track use, typically 8 to 10 minutes, engine has massive stumble when under boost / full throttle.  Data logs show fuel injectors are "skipping" (inj% at 0) during the high boost conditions, but only after 10 minutes of hard running.  This has been a problem for many months.

    Previously (last month) found cracked solder joints at IC7 (5V voltage regulator) that caused a "no start" condition.  Re-soldered and back to running condition but still with stumble under boost.  Found connector pin lead for injector circuit (connector 2Z) with cracked solder joint.  Re-soldered but still have stumble under boost.

    Based on the visual appearance, IC7 has probably been replaced previously.  The re-solder repair of the pin leads to IC7 last month are already showing heavy oxidation of the solder surface.  Only those solder joints exhibit this appearance.

    1) Since I believe IC7 has been replaced previously, is it possible to verify that LM2940CT 5V is the correct IC for IC7 (rather than the LM2940CT 12 V version used for IC8) ?

    2) Is there a possible cause of excessive current at IC7 that would be causing overheating of these solder joints ?

     

    Tom D

     

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