weird issue, need a little help
 

Hello, I picked up a '79 924 that had sat for about six years. I replace the water pump, the external fuel pump, fuel filter, hoses, belts, starter, alternator, fuel injector gaskets and a bunch of other stuff like brakes, etc. The issue I'm having now is car runs real sluggish, it's slow to rap up but it seems to idle fine. After the car has been running for a while it dies and sometimes back fires a few times. I've noticed that when it dies the fuel pump is not making it's normal whining the electric fuel pumps make and you can't start the car again for 15-30 min. Before I started the car for the first time I drained the old gas out of the tank and put in 5 gal. of new gas with a full does of fuel injector cleaner. I hooked up a fused power line from the battery to the fuel pump and ran the new gas with fuel injector cleaner through the system several times. The injectors were spraying nicely and the system was cycling 4 gal. of fuel about every ten minutes.

While looking in the Haynes manual I noticed the power to the fuel pump is routed through the cold start system but I have no idea where or how to start testing to see if the issue lies in there.

Please help

I am not real familiar with your car, but it sounds like you are having issues with the DME relay. It also controls the fuel pump and the contacts may be getting hot and disconnecting. After they cool, the car starts again. I would start with that.

Early 924's don't have DME's. Different injection system.

Might find the answer at 924.org.