Here's my problem.

'87 Camaro 383 TPI MSD Distributor with stock external coil.

The car usually starts. On those days it doesn't here are the symptoms.

Cranks, oil pressure builds (as expected). No spark. If the scanner is attached to the ALDL, or some pressure exerted on the ALDL it starts.

I am baffled that a bad connection at the ALDL can prevent a spark. I even disconnected the computer from under the hood, and it wouldn't start.

I have no trouble codes at all.
Disconnecting the battery and waiting a minute or two doesnt do anything either. I replaced the cap/rotor and the external coil. nothing...

anybody have an idea? would appreciate it. its a fun car when it works.

Check the computer ground and power supply.

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70 camaro 307 (350soon) /350th

If you've got a key with a chip on it, it may be something in the theft deterrent system wiring. That's just a stab but may be worth a thought. I'm not sure if the theft deterrent kills the spark or kills everything.

The 'vats'system which is the key with the resistor in it only shuts off the fuel injectors.I've worked on tons of fuel injected vehicles and have never seen what your describing?Not doubting it mind you just never heard of the data link connector causing a no spark condition.I guess I don't have an answer with out actually 'seeing' this in person.Sorry