2003 ML270 CDI cranks but won't start

[Axcontrols]

This morning it started and ran for 2 seconds but cut out immediately. Now it just cranks but won't start.

It's diesel. Does it have an electric or mechanical fuel pump? Fuse/relay etc? Emergency fuel shut off or whatever it's called?

What should I look for?

Thanks
Ian

 

[Axcontrols]

Update

Ok. Went out and cranked it again. Cranked for much longer than I felt comfortable with. Maybe 10 15 seconds and it started.

Seems to run ok now. But I'm obviously nervous.

Was it just a temporary 'glitch' ? Anything 'on its way out' that needs replacing before it fails completely? In my experience that amount of cranking is what would be needed if there was no fuel in the system (mechanical cam driven pump?) and the cranking was needed to pull fuel up from the tank.

Any comments really appreciated.

Thanks.

 

[carnut13]

Possible crankshaft sensor on its way out? People who know diesels better than I will no doubt suggest the answer soon

 

[whitenemesis]

Could be air in the fuel lines, quite common. Olives eventually harden and let air in.

Crank sensor is usually from a hot start.

 

[Cole@MBS]

As Pete above or a injector leaking off too much fuel!!

 

[Axcontrols]

Car was stood all last week. Not used at all Monday to thursday. But started immediately on Friday and drove fine all day Friday.

If air was leaking in, fuel leaking out, wouldn't that be more likely to have happened during that 4 days, monday-thursday and prevented starting on Friday?

But as I said, it started fine on Friday - and didn't want to play this morning, Saturday.

I'm still thinking it's fuel related though. Fuel draining out of the system back to the tank so had to be cranked for a while to prime the system. Although strange that it didn't occur during that long stand last week.

Once again, thank you for any comments.

 

[WG M-B]

It sounds like fuel leaking back to me too. Try and park it forward facing down an incline to prove the point

 

[rony2rip]

Hi, I've just read your post and would agree that it sounds like you are suffering from fuel starvation. I inflicted the same illness on my own car last weekend after changing the fuel filter. Exact same symptoms as you, start for 2 seconds then dead, crank for a long while then start eventually. After a lot of head scratching and looking I could see aerated fuel in the fuel pipe from the lift pump that goes to the high pressure pump. When the car was turned off the fuel then syphoned back to the filter. I got a set of "O" rings from the local MB service dept 90p each, full system needs 7 but I only changed the first 3 from the fuel filter to the lift pump and the one leading from the lift pump. I then opened the bleed valve, thing that looks like a "syringe" on the pipe that comes from the lift pump located on top of the engine, cranked the engine when fuel arrived out of the valve closed it and continued to crank, car started after 5-10 secs max and has never looked back. Now starts better than ever and no aerated fuel in the pipe. So before you go checking sensors and injectors and all sorts of expensive stuff do the £2.70 repair and see if it works it could be a really satisfying cheap fix. You could also change the fuel filter at the same time but be sure to manually fill it totally full before reconnecting to assist with bleeding the system.
Just a note on the "O" rings, when I took the first one off at the fuel filter the old one looked very like the new one, easy change. The next two old ones were very flat and tight on the fitting they were fitted to. The new ones were slightly bigger and as a result appeared to be too big. I called the garage to check that I had been given the correct part and was assured they were and just needed to be coaxed. I applied a light coat of vaseline and with gentle firm force they eventually fitted in and locked in place.
The other original rings were difficult to get at and without disturbing them I reckoned it was unlikely that they were faulty on my car.
I hope this is all you need to do, give it a go before you go to any major expense.

 

[Axcontrols]

rony2rip. You mentioned "Lift Pump". Where would I find that ?

 

[rony2rip]

Hi Axcontrols

Sorry for the delay inreply I've been off line for a few days. The lift pump is the first component the pipe bringing fuel from the filter is joined to after it has left the filter, moving towards the front of the engine. there are two identical plastic unions on the rhs of the pump as you look at the front of the engine. The unions on the pipes are plastic and push down into the centre of the filter and into the lift pump. you need to be careful disconnecting the connections, there is a "U"shaped clip on each that needs to be pushed to enable the union to be disconnected you may need to gently pry it up/out with a flat blade screwdriver as you carefully pull it away. You will see the "O" rings on the plastic fitting that goes into the filter or pump. I replaced all three of these and then bled the system before starting her up. I wish I'd taken some photos but was too keen just to get the car going again.

I'm gonna try and get some photos on the internet or take some if I have to although the covers are all on again and it will be saturday before I can do this. Hopefully you will be able to establish where and what I mean by what I have written above. let me know how you get on
regards
Ronan