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W124 300TDT Diesel wont start 1991
Mercedes-Benz Mercedes-Benz Cars Discussions (alt.auto.mercedes)
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#11
 
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Re: W124 300TDT Diesel wont start 1991 -
03-26-2007
, 10:08 PM
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On Mar 23, 11:44 am, "-->> T.G. Lambach <<--" <"T.G. Lambach at NoHamorSpamcomcast.net"> wrote: Air bubbles.... That's the problem. Your fuel system has an air leak - at a filter, hose clamp or just a deteriorated fuel hose. Once air creeps in, usually overnight, starting is difficult. That's because air can be compressed (fluid cannot be compressed) so when the injection pump pushes 2,000 psi pressure to the injectors the air absorbs the pressure and the injectors don't open -- until the air has been expelled from the high pressure lines by your expensive cranking with the starter. If you changed a filter check that it's really tight, then check if all the fuel hose clamps are tight and wipe the fuel hoses with a medium dark, not black, rag so any leaks or weeping really show up on the dark rag. You should know the the new ultra low sulfur diesel #2 affects some old, dried out hoses and sealing "O" rings and so, causes leaks. -- © 2007 T.G.Lambach. Publication in any form requires prior written permission. I have been having the same problem with my 1982 300 TDT. Air appears in the in-line filter that is before the priming pump. The air appears to be getting in somewhere between the tank and the engine compartment. I have replaced all the hoses under the hood and checked the hoses between the tank and the metal lines from the tank to the engine compartment, but the air continues to get into the system. It appears that I am going to have to remove the tank from the vehicle and replace all the hoses between the tank and the expansion tank. Does anyone know if bad hoses between the big tank and the expansion tank would put air into the fuel lines that run between the tank and the priming pump? Sounds like we are similarly afflicted. I am going to replace the fuel |
#12
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#13
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To both of you, I suggest you first check the highest fuel line / filters because the air enters the system when the fuel flow stops after shut down. That's because the fuel wants to be at the lowest level so a slight vacuum is created at the high points of the fuel lines like the spin on filter for instance. Think of a siphon - it works so long as it's intact. A bubble inside the small clear plastic filter is OK for it stays there. I'd start at the fuel input to the injection pump and work backwards because the air is probably getting into the IP while the engine is shut down - that's why starting is the problem. -- © 2007 T.G.Lambach. Publication in any form requires prior written permission. |
and the filters. If I park the car facing downhill it seems to help
with the starting problem. The other day I checked the in-line
transparent filter when I started the car and there were a couple of
tiny bubbles caught in the two high spots. Then I drove 40 miles and
opened the hood and looked at the filter and it had large air bubbles
in it.
Does that seem to be saying the leak is back by the tank someplace?
Paul
#14
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#15
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To both of you, I suggest you first check the highest fuel line / filters because the air enters the system when the fuel flow stops after shut down. That's because the fuel wants to be at the lowest level so a slight vacuum is created at the high points of the fuel lines like the spin on filter for instance. Think of a siphon - it works so long as it's intact. A bubble inside the small clear plastic filter is OK for it stays there. I'd start at the fuel input to the injection pump and work backwards because the air is probably getting into the IP while the engine is shut down - that's why starting is the problem. Sounds logical, thanks! |
#16
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Possibly, but don't forget that air expands with temperature so a small cold bubble will be larger when it's warm, but I'd check the hose clamps near that filter. If the ONLY problem is during starting the problem is very close to (or at) the injection pump but if there's sputtering DURING driving the air leak could be back at the tank's hoses. -- © 2007 T.G.Lambach. Publication in any form requires prior written permission. |
Once the car is running the engine runs perfectly with good power and
no misfiring. I have replaced all the hoses except the semi opaque
plastic ones and have replaced and tightened all the clamps and
installed a new priming pump. Those things were all done some time
ago, and I have stopped getting air bubbles in the semi opaque lines
that run between the big spin on filter housing and the injection
pump.
Are there seals in the pump itself that may have begun to fail?
Paul
#17
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