Actually, when you jumper the 2 pins in the ALDL (diagnostic plug) you put the ECM in "read trouble codes" mode.

To be able to check/adjust the spark advance, you have to disable the Electronic Spark Control (ESC).

To do this, go into the console (likely under the front pop-out tray) and find the wire that has an inline connector. Should be the only one in the console like that. It'll either be a white wire with black stripe, or black wire with white stripe. As I recall, mine was wht/blk.

Normally this wire is connected to enable the ESC. What you'll want to do is unplug the wire from itself.

This will do 2 things: energize the "check engine" light/set a trouble code, and disable ESC.

Then you'll be able to slap a timing light on #1 cylinder and read the scale on the timing cover.

Note that it'll idle a bit doggy with the ESC wire disconnected, but that'll go away when you reconnect.

BTW if you adjust the timing to around 12 deg BTDC or so on a stock 2.8, it'll run just a bit better.

Don't forget to reconnect the ESC-disable wire when you're done! The check engine lite will go off, and the trouble code will persist in the ECM for a set number of start/restart cycles, but will eventually clear.

HTH & let us know how it goes...........ed