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Andre Loots

No start issues resolved

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For a while I had starting issues with my E39 530d.  I had studied many such cases but could not find a solution.


The story goes like this.  I had to begin cranking the engine longer before she started, and sometimes I had to crank twice before she fired up.


One day I got stuck at a filling station when I wanted to check the tyres.  When I tried to turn her on, she just cranked and did not start.  After having her towed to my house, I began checking everything. 


I checked relays and fuses to make sure the diesel pumps worked.


I did an injector leak off test and found that one injector was leaking off much more than the other 5, so I replaced this with a new injector.

The vehicle started first time afterwards and ran for about a week after this.  Then she began with her nonsense again.  The error code was "low fuel rail pressure on start".

I had the intermediate diesel pump replaced - no success.  I checked the in-tank pump pressure - 1.2 bar, which is sufficient.  I installed a non-return valve on the diesel supply line from the tank - no success.


The fuel rail pressure sensor was giving readings when the diagnostics machine was plugged in, so I ruled this out.  It dawned on me that the unit controlling the pressure was the pressure control valve which is located on the high pressure diesel pump mounted on the engine itself.  I purchased a new pressure control valve and as soon as I had a chance, removed the inlet manifold to access this part.  Upon removal, I found that two little o-ring gaskets had split and wondered whether I could have just purchased two new o-rings.


Anyhow, I replaced the old unit, and before putting everything back together again, prayed a prayer and cranked her up.  She started, first attempt.  End of my 3 month torment of having to drive my expensive F10 M5 for work.


I know the E39 is old and many people no longer drive them, but if anyone is experiencing the same problem, I trust this will assist.


Split o-ring on diesel pressure control valve  


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Failed o-ring on pressure regulator is quite common. The most common reason for low rail pressure if supply pressure is sufficient and leaky injectors are ruled out. Those seals can be bought separately for about £10.

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As above.  I tackled the pressure sensor first, just bought a new one after crudely trying to do a leak-off test only by removing the pipes and seeing diesel go everywhere.  Nothing looked suspect to sensor got changed.  The o-rings were dead so I assumed it was that.  Starting was slightly easier but still no good


Bit the bullet and did a proper leak-off test (the kit is only 20 quid) and one was totally dead.  Replaced and she fires mint now.  Pre-supply pressure should be 4.0 bar.

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