Is this fuel pressure normal ???
 

I hooked up my fuel press gauge on my w124 to the main line comming from the tank where it hooks to the fuel distributor and the pressure was off the chart !The gauge only goes up to 150psi and it went all the way around to the zero pin! when the eng is shut down it goes down to 55psi. Then after 15 min it goes down to 45psi.
Did I connect the gauge to the wrong place? Should I connect it to the other side of the fuel distributor where it goes to the fuel press regulator?

I am pretty sure the fuel feed pressure from the pumps to the distributor should be around 90-100psi tops. And when turned off it should hold 60+psi for hours. If it leaks down the accumulator at the pumps is probably bad...or the fuel pressure regulator leaks....or the injectors are leaking down. Is it hard to start? especially when warm?

My 126 car has a fuel pressure regulator right at the fuel distributor - I measure fuel pressure at the fuel distributor which would be past the regulator and thus lower pressure! Don't know if your car is similar?

All MB gas engines if this era have a fuel pressure regulator right before the fuel distributor.

I did some research and looked at WIS and found I had the gauge system connected the wrong way! I was reading full unregulated pressure at the pumps. There is a port on the lower half of the fuel dist you hook up to and the other hose goes to the upper chamber by removing the line for the cold start valve and hooking up to that port. Readings were normal when I did it the right way. upper chamber reads 80psi lower is 69psi It holds pressure for many hours but goes to zero after about 14 hours. Sometimes it starts good cold sometimes not same when its hot sometimes it fires right up and the other times you have to crank it a whole lot