Thanks for the feedback on your car. Apparently I was not the only one not familiar with the letters and a B21 in an '85.

Iam not home with my Bentley book or my 78's green books but 50 psi control presure does seem to me to be too high.

As I remember the injectors run in the neighborhood 32+ psi in order to open. There is a maximum but I forget that one. Each injector is feed by perimeter pistons slots of the fuel distributor that pretty much regulates volume along with the frequency valve per orders of the ECU and the O2 sensor.
The whole setup is like a mechanical AMM thas on the LH system.

The contol pressure regulator controls the flap hold down pressure during cold to hot operation so it should vary in pressure from its own internal electric heater.

I would think the control pressure is probably only a few psi more that the controlled injector pressure. Someone might be able to find you that exact range of specific psi tolerance.

On the pressure testing hose setup you should have three separate readings. Line from the pumps, the flap control pressure and the injector pressure.

I found it interesting that you know someone who recalibrates these regulators too.

I have read that in most cases its a little wear around the heater fulcrum or a dirty filter screen or two that gives them hee bee jee bee's! Their so reliable its got to be a minor repair if you have parts or skills.

Probably the same with the LH's AMM's. Isn't that always the case?

I have seen where dealers try to get hundreds of dollars for new ones. I doubt Volvo paid out great amounts of money for them in quantity or we would not have even able to afford the car at their low production levels. Bosch probably put them on many makes or systems at the time.

I would like to add that if this does lead to any resolution, you might try changing the spark plug gap a little tighter by a few thousandths of an inch.
I have found that on some lean burning cylinders or oil fouling cylinders the decrease helps. Just in case there is a blowing out of the spark or fouling to ground under either condition.

Good luck tomorrow.

Phil