BMW E24 633Csi Start Stall Problem; High Fuel Pressure?

[Bullit71]

Hi — I got a couple of questions regarding a start-stall problem I’m having with my ‘83 633CSi (2/83). The car will start on 6 cylinders run for 1-2 minutes and stall out. Restart takes a couple of tries with the same result.

When one of the fuel injectors is disconnected the car will run for an extended period of time on 5 cylinders. As soon as the 6th injector is connected the engine stalls immediately (does this regardless of which injector is disconnected). Connected test light to 6th injector connector and it lights/pulses when running on 5 cylinders.

Initially the problem with the car started with no start problem that seemed to be resolved by replacing the cold start valve.

This problem started shortly after that. In-line pump started making a straining noise shortly before stalling and also when running on 5 cylinders so we replaced in-line fuel pump and filter to no effect.

Replaced main relay, fuel pump relay, and Motronic unit. Car seems to be easier to restart but stall problem continues. Checked the fuel pressure and we noticed that initially while idling the fuel pressure is around 40psi but then spikes to over 100psi just before the engine cuts out. Couple of times when testing the fuel pressure the pressure was so high it blew off the hose off the tester right after engine stalls.

We are looking to replace the Fuel Pressure Regulator this week to see if that might help. Has anyone else experienced this? Why would the pressure spike with 6 injectors connected and not with 5 fuel injectors connected? Will the replacing the fuel pressure regulator fix this? Any advice is greatly appreciated —

[m6dave]

Check the return to tank line from the fuel pressure regulator is not blocked or obstructed before you replace the fpr.