Hi i have a 300d with om603 original#14 head it was starting pretty good till one day i changed all the glow plugs i used bosch ones. Now it is harder to start. I changed them onl because they were burning out 1 by 1 and i just got sick of replacing them with used ones. Anyone got any ideas. And they all do work

How's your compression? Have the delivery valve seals been changed recently?

Not sure on compression but it runs perfect as soon as it fires. And the problem only started after i changed all 6 glow plugs. I threw out the packaging and wondered could i have gotten the wrong part number maybe like a similar one and didnt realise.

Ehhhh the glow plugs aren't your problem probably. If you put new ones, it's pretty rare if you got a reputable brand that they're bad out of the box. If they were, you would know as well and get a 24/7 glow plug light. If they fit, they're right too... If you had a compression issue, you'd be seeing smoke at cold starts and start losing some power over 50mph. I'm sure you probably have a fuel leak at the delivery valves or on the injection pump elsewhere causing these cold starts.. Look for leaks at the delivery valves, lift pump and fuel warmer (directly below the lift pump).

I hate to say the obvious too but... With this cold weather how good is your battery? Diesels require a lot of cold cranking AMPs and these cars also need a group 49 battery (it's a truck battery) to start in the cold easily..

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

The glow light comes on for 5-10 seconds on cold start? How about letting it glow for 30 seconds or until the glow relay clicks off (ignore the glow light) before starting? Check the resistance of each glow plug between the socket at the glow relay connector and a solid engine block ground. Anything less than 0.7 ohms or more than 1.0 ohm is suspect.

Sixto
83 300SD
98 E320 wagon

I will try letting it glow longer and see i can check resistance but i think all glow plugs work since ot doesnt miss when it starts. All the insulation rotted off the wires going to the glow plugs at the relay so they are all touching but i doubt it matters.

Sounds like you found the source of your problem.
Time for a new/used/bebuilt harness.
You can use the heavier gauge stock wires from earlier glowplug harness to rebuild yours, or buy a new or used harness instead.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

Will the wires touching cause trouble since they all come on at the same time.

If they were all supposed to be on the same wire, Mercedes would have built it that way.

It may be a good idea to check the strip fuse in your glow plug relay for cracks or broken areas. If you have bare wires, it's possible you've grounded against something in the engine bay and blown the fuse.

For further thought - bare wires cause fires.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

Yes it will cause trouble, when the wires touch - two or more of the glowplugs will be wired in series (like the old style loop plugs).
Not a good state of affairs...glowplugs will not operate as intended, and like Diseasel300 said, there is the possiblity of an underhood fire

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

Get the battery checked it could be weak.

GP wiring harnesses on these cars do fail, ask me how I know. After replacing GPs I accidentally pinched one of the GP wire terminals between the head and intake manifold as I was installing it. Didn't notice it, turned the key to glow, lots of smoke from the harness and, quickly turned it off but the damage was already done. You would think the 80a fuse on the GP relay would protect against this kind of accident but NOPE.

So I built a new GP wiring harness with 10awg wire.

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Thanks guys i will make a new harnes and see how it works

Fixed all the wiring and no differance as one guy stated let it glow longer after light goes out i did that and yes it starts a bit better. Once it gets to - 10 it wont stsrt at all is that normal.

Did you get your battery checked?

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The prechambers might need some reaming.

Do these things start at -10*F without an external heat source?

Sixto
83 300SD
98 E320 wagon
Hi