No fuel pressure

[Elizabeth96]

Good day

We have a C270 cdi.
We rebuild the engine and wont start as there is no feul pressure. We did replaced the hp feul pump and the low pressure pump. What can it be?

 

[mersum1es]

Which engine it is, OM612 or OM647? Fuel systems are different, different problems... but injector tank line leaks are one thing which is possible culprit for both, you can measure it pretty easily.

 

[Elizabeth96]

Om612, how do i measure it?

 

[mersum1es]

Om612, how do i measure it?

In that case, first check your fuel lines on hp pump are in right order. Most common rebuilt fuel lines - non starter fail. Frontmost hole connects to rail.

Then check is there air bubbles running in clear low pressure fuel lines when cranking.

 

[Elizabeth96]

Thank you will check

 

[Elizabeth96]

The mechanic that works on the car tested it and still the car doesnt want to work. Can you perhaps send me the fuel supply diagram. Or can there be another problem.

 

[mersum1es]

What has been tested?
What is rail pressure reading during the crank?
If below 150bar, Is ther air bubbles?
If no, what are Injector leaks?
If ok, is there fuel coming from aux pump to hp pump (hose between them can be removed, and then tried to crank - beware some fuel will spill out)
does system have shut down valve in hp pump motor side hole, if yes, check wirings of the valve and check valve inside pump is not jammed.

 

[Elizabeth96]

All fuel lines has been tested for blockages and damages. Rail pressure reading during the crank is 5 bar with no air bubbles.
Injectors was replaced. Yes there does come fuel from the aux pump to the hp pump. Fuel supply to the hp pump is sufficient but fuel does not exit the hp Pump at all. There is no shut down valve.

 

[mersum1es]

Was hp pump removed during rebuild? Pump connected right to cam (key slotted adapter in place)?

HP pump was not opened?

Replacing injector does not tell anything, unless they are brand new. Measure tank line leak.

Pressure relief valve checked (there is also o-ring on valve body, which rarely has been broken), see if fuel is coming valve return line.

 

[Elizabeth96]

Do you know of anybody in SA that is a good Merc mechanic?

 

[mersum1es]

See my location

sorry no idea

 

[Taffy7hfa]

If they have been stripped down the fuel systems on these engines can be really difficult to bleed, try a little easy start, might help draw the fuel.

 

[mersum1es]

If OM612 is spilling fuel from aux pump, its not bleeding issue... ( AND no air bubbles...)