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Can anyone tell me why the fuel injectors are shut down after starting?

1986 535i with Motronic Basic.

Any help much appreciated

Thanks

Faulty reference sensor?

Reference sensors check as good. Any other causes for fuel injectors to be turn off by computer after starting?

No airflow indication from the AFM would be another.

The injectors are supposed to have power fed to them from the main relay once the ignition switch is switched to on, after going thru the OBC relay, which has been known to be problematic, but I doubt it since it will start even if it dies.. So first verify that you do have power to the injectors. If not, figure that out. If you do have power to them, the ECU is supposed to turn them on by grounding them.

Main relays are known to be cranky, but it doesn't sound like it this time. A really long shot is a bad ignition switch supplying power to the coil of the main relay while in crank mode, but not in run.

Link to the wiring diagram. http://wedophones.com/BMWManualsLead.htm

ECU also cuts fuel when the TPS signals idle (closed throttle) and RPM are above ~1250.