glow plug light and misfire w 124 e300 diesel

[gilesp]

I have starting issues on my w124 E300 diesel. I have replaced the temp sensor and glow plug relay and checked that all glow pugs are working. The glow plug light comes on when the ignition is turned on, it then goes out the engine starts but with a cloud of smoke out the back and a seeming missfire. The glow plug light then comes back on again for anything up to one or two minutes.
The engine once warm runs well apart from occasionally it develops a minor misfire and when you take you foot off of the accelerator and come to a stop , the engine dies and you have to crank it a lot to get it fired up again. This happens in a completely random fashion but usually after travelling at a constant speed for a time. Any ideas??

 

[bolide]

How many miles has the car done and when was it last serviced? Has it been sitting for a while? Are you using comedy fuel (veg oil, etc)? Have you had it long? Has it always been like this? Have you had work done on it recently? Is the person who replaced the glowplug relay an expert on these cars?

It must be suffering from fuel starvation - one running these engines don't tend to stop again and, if they do, it's due to lack of fuel

Look for air bubbles in the fuel pipework. Make sure the fuel shutoff is opening fully. Replace the fuel filter & pre-filter with new MB parts. If it still gives problems look for blockages in the fuel feed pipe and / or a blocked tank strainer

The glowplug light coming back on means there is a faulty glowplug or a fault in the system somewhere

Nick Froome

 

[gilesp]

Thanks for guidance, Nick.
Car has done 204,000 and has been used by me for the last 3 years and travelled 60,000 miles serviced by same garage. The problem with the fuel issue has been evident since the vacuum pump was replaced some 15,000 miles ago. I replaced the glow plug relay but the glow plugs were checked by garage at last service when all filters were changed. Having just gone out and checked there appear to be air bubbles in the two pipes attached to the top of the fuel filter housing.

Giles

 

[SilverSaloon]

one or more glow plugs are dead - simple.

you also need to replace the clear pipe orings to sort the fuel bubbles.

i suggest you try another garage, as it appears they havnt properly checked the glowplugs

 

[bolide]

The fuel issue is probably caused by the fuel pipework being disturbed when the vacuum pump was replaced. I'd do all the O-rings as SilverSaloon suggests

Glow plugs are easy to test with an ohmmeter. Pull the 6-pin plug off the relay and meter each pin to earth. The plugs should be 0.7 Ω each. This way of testing tests the glowplug & continuity of the cabling

If they test OK test the voltages at the relay when the glowplugs are on

Nick Froome

 

[gilesp]

Thanks SilverSaloon and Bolide. I will endeavor to find another garage, in the mean time I will check glow plugs and get o rings for fuel pipes.
Anyone know of a good merc mechanic around Bath or Bristol ??

Giles

 

[gilesp]

I have now changed two of the clear pipes, obtained from local merc garage. I discovered that the third pipe had a different fitting on the bottom, after the parts department had spent 20 mins looking through their computer it transpired that the bottom fitting had been changed for a bolt and banjo in a recall in 1995. Mine still has the original fitting, can't complain if the pipe has lasted 20years and 204,000. Parts dept has bolt on order, they tell me that the existing hole will either be threaded internally or the bolt will be self cutting.
Is this correct if any one knows.