Sunday, September 22, 2013

Bleeding Diesel Injectors

The fuel system is self-bleeding during starting. This is due to the increased delivery rate of the fuel pump, the restrictors in the filter upper part (73), and the injection pump.

Air in the injectors as the engine will not start. To bleed air loosen the outlet banjo bolt on the filter and cranked the engine until fuel came out, but apparently air has gotten beyond the filter into the injection pump/injectors.

The basic procedure which helped is :---
Just wanted to say I loosened the banjo bolt after changing the fuel filter on my S350 TurboDiesel. After cranking a few times, the air was purged from the line and the engine had started.
Fuel was splattering everywhere, but I quickly ran to the front of the car and tightened the bolt until no more diesel was leaking.

After a few minutes of cleaning up, the car started without any problems.

DO not crank the engine it will screw up the high pressure pump.Remove the pipe which goes from the filter head to the high pressure pump.Then you need a suction pump or priming bulb to pull diesel up from the tank and fill the new filter.Pump till diesel comes out of the filter head reconnect the pipe to the filter and start the engine.

The three lobe high pressure pump will not lift air and if you spin it over with no fuel in the lines it will score the pumping element bores and pistons.

they are self bleeding, usually if you just carry on cranking the air will be pushed through & the engine will start. try this first (really needs cranking for 20-30 secs I would say)

however, occasionally they are more problematic. If the fuel is drained out of the filter, then fill this first.

you can also slacken off the union for the feed from the high pressure fuel pump to the fuel rail & crank over until fuel comes out. tighten up union again & the engine should now start.

there are 2 pumps on the front of your engine - 1 is the low pressure pump (see attached picture), this draws fuel from the tank through the fuel filter & supplies the high pressure pump - the high pressure pump is the larger one that sits below this. the high pressure pump is the one more prone to failure, but it would appear that the low pressure on in your case is not delivering the fuel.

you need to see if the low pressure pump is working.

you can disconnect the inlet side to the fuel filter & connect a hose & place this into a container of fuel. refill the fuel filter again. disconnect the outlet pipe from the low pressure pump that goes down to the high pressure pump & crank to see if fuel flows out. If not then the fault could be the low pressure pump, but im my experience this is fairly rare.
If fuel flows out then connect the line back to the high pressure pump & see if fuel come out of the high pressure line.

it may be the system is pulling in air from a poor seal on one of the hoses - this is more common than the low pressure pump failing.

bleeding fuel system on mercedes

that sorted it out & the car has started. I fed fuel to the filter with a hose and a small funnel, when I cranked, air moved up from the HP pump to the LP and right back up through the funnel. As soon as the system filled, the engine started.

the fuel leak near the low pressure pump is usually just the seals on the fuel lines. the seals are available as a separate part & are just a few pence (or cents!). care must be taken when removing the lines as they have clips on that can go brittle with age.

This will help.

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