Can't Start my 300D - PeachParts Mercedes-Benz Forum

frogboy · #1 01-30-2003, 06:43 AM

I don't know what is wrong, but I can't start my 1977 300D for some reason. It is turning over, but the glow plug light does not come one. Well I replaced all of the glow plugs (old filament type), and I replaced the air filter, but my car still won't start. Somebody told me that it is probably going to be something wrong with my fuel system, but I just wanted to get any feedback that anybody might have for me. Thanks

engatwork · #2 01-30-2003, 07:03 AM

Is the glow plug light still not coming on after changing them? If so, it sounds like the glow plug relay. Try "jumping" straight from the battery to one or some of the glow plugs with a piece of heavy wire. If it starts don't forget to remove the wire

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#3 01-30-2003, 08:27 AM

Put a voltmeter on one of the glow plugs to see that there is voltage. If not, check the bar fuse in the little plastic holder on the firewall just behind the engine. Do not think that it is good just because it looks good. Vibration over the years will cause a minute crack at one end that you cannot see. Disconnect the battery ground cable and remove both screws on the fuse to ensure that it is good and solid.

If you have voltage on the glow plugs, then you might need to adjust the valves. You also should crack open an injector line and turn it over. When you turn it over, fuel should dribble from the fitting, if not, you have a fuel delivery problem that you need to track down.

Good luck,

frogboy · #4 01-30-2003, 02:37 PM

My glow plugs do not have a relay because they are the old type with the wierd wire that goes from one to the next all the way from the front to the back, but will try the voltmeter on the glow plugs and the cable connected to the firewall. Also I think that it will probably end up being a fuel delivery thing, so I guess that I will have to check that too. Will report back to this thread with the results. Thanks

#5 01-30-2003, 02:53 PM

Yes, it does have a relay. On yours it is behind the instrument cluster.

If you have voltage to one of the plugs, then the relay or fuse is not the problem. If you don't have voltage, post again and we will start walking you through the troubleshooting steps.

Good luck,

frogboy · #6 01-30-2003, 03:39 PM

Right now I'm off to the parts shop to get some fuel filters. The reason being is that I have a friends 300D, and I looked at the clear filter next to the fuel primer pump, and it was still clear, but mine is completely black, so I think that there might have been a bunch of gunk in the fuel tank that got sucked up into the filters because the car was low on gas when I bought it. Will keep you posted

frogboy · #7 01-30-2003, 06:44 PM

Okay, so here is the update:

I replaced the primary and secondary fuel filters, and I measured the voltage on my glowplugs, my battery, and I checked the cable that is attached from my glow plugs to my firewall. I turned it over a few times, and it worked!!!

But now my question is since I got it started, should I run it down to near empty, and clean out my fuel tank of all the sediment and sludge that is in there?? I feel that to be safe I probably should, but then how would I go about doing that?

All I can say is at least my car started, and I drove it around for a half an hour or so without turning it off. I will go and try to start it later today to see if it still works though.

lrg · #8 01-30-2003, 07:18 PM

Watch your new (clear) filter. If it starts to get black again and/or you see some black chunks floating around then you likely have an algae problem. You will keep plugging filters until you get rid of it. I'd recommend keeping a couple extra prefilters (the clear one) on hand just in case. If you have algae, order some Diesel Doctor or go to a good marine store and get some diesel fuel additive that clears up algae. Unless you drain the tank, plan on changing the filters, all the dead algae will eventually come out to the filter.