I have been through this several times over the years, weather cools off a little, the diesel won't start.

This one is pin type glow plugs, and I've always been able to fix them by screwing in a complete new set of glow plugs. It didn't work this time.

Back when I was having other problems, about 5,000 miles ago or less, I checked the compression. It was 300 pounds within about 5% on all five.

It is trying to hit on a cylinder or two, but won't start. I checked the voltage at all five plugs, it was about 9.75 to 10.5 volts at each one. The relay leaves them on for awhile then turns them off, seemingly normally.

I have not checked the fuel system in detail, but I can tell by the smell and the smoke that there is fuel going in the cylinders.

Any ideas? I'm on new ground here, because I've always been able to screw in new plugs, and as long as they're getting voltage, the dude will start. The exception, of course, is the old 240D with the worn out interim engine. It won't make enough compression to start. I understand what gives with that one. This one has me a bit stumped.

I have not checked the vacuum to the diaphragm on the pump yet. Since it takes vacuum to kill it, I assume that I can remove the vac line to determine if this is the problem, which I doubt that it is.

Thanks for any help that anyone may be able to offer. I will be able to get back to it tomorrow night. If I don't get any other suggestions, I may do another compression check.

Thanks in advance,

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Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

Say Larry, How cold is it getting where you are at in Texas? Is it cold enough to plug in the block heater? And if it is, why not plug it in and see if that helps any? This one has the little enrichening knob, doesn't it? No dice there though, 'cause I am sure you've tried that. And I am sure that you tried glowing it several times too. Let us know what else you observe, I am sure someone will have an idea.
-Larry

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03/83 300D 184k
07/73 280 (sold)
'88 other 168k

Larry,

Did you check the valve clearance?

David

Larry, my friend has your same car. '81 300d.
Same problem but not symptomatic with cols weather, just did not start
but glo plugs o.k. Did the fuel filter basics etc. no problemo.
Ended up changing the fuel
pump for the heck of it cuz he got discount at dealer parts.
Bingo. Unexplainable to him because
he saw that fuel came out of the line o.k. prior
to replacement. Says it has better pick up now also.
Good Luck

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1979 300D
133K miles
1989 300SE
1995 C280

Larry,

It isn't very cold, it was in the 40's the morning she had trouble and I've tried it when it was much warmer.

be459,

The valve clearances were adjusted just a few thousand miles ago when replacing the valve seals.

unkl300D,

I will keep the lift pump in mind, in case I need to get that deep. Since I smell the burned fuel from the exhaust I don't think this is the problem, but I'm not ruling anything out yet except the glow system.

Everyone,

It dawned on me when driving in this morning that I noticed the fuel guage was pegged out FULL. She must have topped it off and driven straight home. Then it would not start. I expect that she either got a bad tank of fuel(which I doubt because I've driven well over a half million miles in Benz diesels and have never gotten a bad tankful) or she filled it with gasoline.

Thanks to everyone, and I will let you know what I find. In the interim, please don't hesitate to post any other suggestions/thoughts.

Have a great day,

------------------
Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

If the valves are properly adjuted (the book says 10mm intake and 30mm exhaust; I set 15 and 35, repectively) is ok and the compression checks out, then be sure your chain is not too badly stretched. Aside from other dangers, a too-stretched timing chain can make starting difficult. Is your timing chain tensioner good? Finally, have you reamed out the glow plug holes when you installed the new glow plugs? Too much carbon there could also cause the problem you describe. How potent is your battery? There is not much margin on these diesels, so an aging battery can cause problems starting. How about timing of delivery of fuel (dreaded drip tube)? The book says one second/drop, but in fact between 10-19 seconds per fuel drop is optimum.

Forgot to mention one more item: plugged fuel filters. Sometimes the one in the fuel tank gets plugged and only passes fuel intermittently.

Douglas,

Thanks for the respones.

As I mentioned the engine has been gone over thoroughly very recently. The timing chain has ZERO stretch, valve seals replaced and valves adjusted, timing checked, last night replaced glow plugs and checked each one individually for voltage and they seem to stay on long enough.

I've glow plugged it several times for as long as the relay will stay on, barely tries to fire.

As I said earlier, it dawned on me this morning that the fuel guage was pegged on full. I think my daughter filled it, drove it home and it would not restart. I expect that she got a bad tank of fuel (unlikely) or she filled it with gasoline.

Thanks again to everyone for suggestions, help and concern. Life will go on, including the life of her old car.

Thanks and have a great day,
Larry

Check how long the glow plugs stay on. Should be about 35 seconds even though the light may go out sooner. If they do not stay on enough they won't get hot enough to start in cold weather.

I would also check the fuel pressure going into the injection pump. When starting the fuel pump is going very slow and a weak fuel pump may not create enough pressure to make enough fuel flow into the injection pump. It also could be bad valves in the fuel pump. I am having this trouble with mine now. Try pumping on the hand pump while someone turns the key to crank the engine. If it starts, your trouble is the fuel pump.
P E H

What about the fuel return line? You mentioned the tank is full, maybe it can't properly retunn the fuel.