Engine began to hesitated then died

[buster1015]

I was engaging in some spirited driving last night with my 1987 911 turbo and it was running great. Then, I began to hear some sort of buzzing or humming but still running fine. I thought it might be the stepper motor for the boost controller which sometimes makes lots of noises which is normal. Since this noise was different than I'm familiar with I began heading home to check it out.

As I was pulling away from a stop the engine hesitated as if a cylinder or more didn't fire. Within a minute the hesitation was significantly worse and engine running very rough requiring a significant amount of throttle input to maintain speed. I shut it off and coasted down the hill to my house and pushed it back into the garage.

Background I recently did a top end rebuild with new rings and a valve job and added a J&S safeguard and a wideband O2 sensor with AFR gauge. Also new spark plug wires, caps were still in good shape so did not replace. About 100 miles since rebuild and it has been great until now.

Applicable Specs/Mods (these were done many years ago)
Twin turbo
Motronic ECU (car was originally a carrera and a turbo motor was swapped in)
Protomotive chip and fuel pressure regulator
Injectors upgraded
Twin plugged with 964 distributor
2 MSD 6AL

My initial guess is the problem might be in the fuel delivery system. I've read through my shop manual and will begin some of the recommended tests but I really don't know where to start.

Any ideas what I should check first?

[fitchn]

Although your car sounds much newer than mine, a sudden loud buzzing is usually the fuel pump dying. No offense intended, but were you rather low on gas at the time??? The reason that I ask is that my pump gets significantly louder as the fuel level drops below 1/4 tank or so.

[buster1015]

Hmm, a dying fuel pump would make sense. I'll check that tonight when I get home.

I was at 3/4 of tank at the time but I understand what you mean about the running low on fuel.