When the car is cold, I have a clicking sounds coming from the fuel pump relay under the rear seat. Once the car is warm, the clicking stops. Performance is normal when a operating temp. When the clicking is taking place, the engine stammers at the cadence of the clicking. Fuel psi bounces to the same cadence at the fuel rail test port. At operating temp, psi is steady and normal.

I've replaced the pumps and the fuel pump relay and still have the same symptoms.

Suggestion?

92 400e 260k well maintained miles

__________________
Jeff
'87 300E
'92 400E
'06 ML350

...did you ever figure out what the cuase of the relay clicking when cold ?
I have the same issue. Thnaks

It was indeed the LH module in the ECU box. One or more of the capacitors (think that's what you call them) on the board had decayed to the point where the circuit board was damaged. I was able to locate a used replacement that was good.. Everything works! ...NOTE - be extremely careful when replacing the control unit. the plastic carriage that the board plugs into can be very brittle and the sockets can be pushed in such that some pins do not seat properly. In my case, I had a non existent Lambda control circuit so the car ran very rich and air/fuel would not regulate. I had to completely remove the ECU re-secure the plugs in the carriage and careful reinstall. no issues since.. all control functions came on line.

__________________
Jeff
'87 300E
'92 400E
'06 ML350