Pressure regulator valve in fuel distributor. Non return/one way valve at fuel pump. Fuel pressure accumulator. Other miscellaneous leaks at injectors etc that your test hasn't covered.
Does the Mercedes fuel pump relay run a prime cycle when the key is turned? My Audi does not, making loss of pressure turn into hard start problems in a hurry!
Why would pressure loss over time affect starting? There is full pressure when trying to start the engine. Perhaps a crankshaft position sensor problem.
My M102 (same injection but 2 cyl less) takes 4ever to cranc cold as well, the colder it is, the longer it takes. With engine heater on for an hour, I just have to look at the key it starts. (North sweden) New injectors, but the rest is old. Something is leakin' by or isn't opening properly. The cold start valve should start working below +7°C or +45°F, managed by a coolant temp sensor. My valve gets voltage but doesn't seem to open.
Pressure regulator valve in fuel distributor.
Non return/one way valve at fuel pump.
Fuel pressure accumulator.
Other miscellaneous leaks at injectors etc that your test hasn't covered.
I would guess the fuel accumulator which is next to the pump and filter!
Accumulator! I should add to test, see if it leaks out the small hose. I bet it does.
Accumulator and/or check-valve I guess
Pinch fuel pump hose to see if pressure gauge is holding pressure. If it doesn't -need fuel pump check valve
Good troubleshooting tip
Does the Mercedes fuel pump relay run a prime cycle when the key is turned?
My Audi does not, making loss of pressure turn into hard start problems in a hurry!
Test fuel pressure regulator, fuel pump check valves, fuel accumulator, leaky fuel injectors
Fuel Accumulator
Why would pressure loss over time affect starting? There is full pressure when trying to start the engine. Perhaps a crankshaft position sensor problem.
check valve or possible leaking accumulator. I would check the check valve first
Injectors are probably not sealing so there is some bleed through. Does the car smell after starting? Any smoke?
My M102 (same injection but 2 cyl less) takes 4ever to cranc cold as well, the colder it is, the longer it takes. With engine heater on for an hour, I just have to look at the key it starts. (North sweden)
New injectors, but the rest is old. Something is leakin' by or isn't opening properly. The cold start valve should start working below +7°C or +45°F, managed by a coolant temp sensor. My valve gets voltage but doesn't seem to open.
Accumulator valve or weak diaphragm
Injectors leaking, accumolator failure, or both.
Accumulator check valve
check valve maybe faulty
LS swap😇
Came here for this. Or put in a modern fuel injection system. Some work required, lol!