89 SL WILL NOT INITIATE OPERATION

[PhotoFanatic]

- The issue emerged many months ago when I used the accelerator pedal. The frigid engine cranked but failed to ignite. I was informed that I had flooded the engine; after waiting five hours, it began immediately.

- Last week, my wife was in the store; the engine was warm but failed to start. After about one hour, it began without issue.

- The vehicle is parked in a warm and dry garage at home. The engine was cranked many times for up to eight seconds without any indication of starting. Upon opening the trunk, a humming sound was heard when the key was in position #2, but no sound was present with the key in the off position.

- Eliminated gas cap - no pressure release - same outcome, no ignition

Kindly provide guidance. Thank you.

[thinkshooter]

The first picture that arises is a defective fuel pump relay.

The solder connections on the printed circuit board may break, resulting in an open circuit that disrupts the electrical supply to the pumps. This disorder will first manifest intermittently and without discernible pattern.

I experienced this with my 500SEC. The technician removed the lid and indicated the location of the problem on the board.

[thinkshooter]

[thinkshooter]

I resoldered them and have been satisfied for the last five years. I maintain the cheap Chinese replica relay in the vehicle as a contingency measure.

[EcoWarrior]

I previously had a '86 Audi Turbo that exhibited a similar issue, which was quite frustrating. Once initiated, it inexplicably continued to operate. The issue was identified as fractured solder connections in the FPR, similar to the one mentioned above. I deduced that the resistance at the contact site progressively deteriorated owing to pitting, resulting in overheating until the solder oxidized, became brittle, and detached from the PCB. I believed that after the engine was operational, vibration facilitated the temporary connections of the pins. Re-soldering and cleaning the contact points resolved the issue thereafter.

[DigitalNomad]

Generally, the engine starts and operates normally while cold; but, after turning it off briefly when entering a shop, restarting the heated engine proves challenging. This problem is often attributed to a faulty accumulator.
I had this issue with both my 380SL and 560SL, and changing the accumulator resolved it.
I consider the URO component to be equivalent in quality to the Bosch component.

[AutoFanatic]

You state that a cold engine fails to start, indicating that the accumulator is not the typical cause for hot engines not starting. An individual previously proposed a relay. That is my hypothesis as well. Best of luck. Intermittent problems pose significant challenges for diagnosis.

[VirtualVoyager]

FPR