W123 Non-Start

What would cause a W123 1979 300D diesel to NOT FIRE at all, after changing glow plugs?
Glow plugs are reinstalled and the electrical series correct according
to glow plug wiring diagram.
Other factors are that the glow plug light stays on about a minute too long, causing the serial connector wires to turn red hot. Also, after the glow cycle, the light goes off, and then about 30-45 seconds later, the relay terminates power and the wires stop glowing red. When the ignition switch is turned over to "start" the glow plug light comes back on again, but the engine does not start.
While the engine would at least fire before the glow plug change, now it just cranks and no ignition at all.
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Since your valves are adjusted... glow plugs are new and assumed to be working properly. I would say the next step is the fuel.
Using your handpump on the injection pump, pump it and make sure there is no bubble in the sxternal filter unit (the one will clear plastic casing and tiny filter inside attached to the fuel hoses.
Are there any fuel leak anywhere on engine?
I would try cranking the engine over with gas pedal depressed... how much? Full throttle to see if it come alive... if engine starts and yet very rough even under full throttle... hold it at 3/4 throttle until it smooths out. This is symptom of air in the fuel line.
Did you change fuel filter before you had starting problem?
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This sounds plausible, despite there having been no problem prior to the change of the glow plugs.
Fuel filters are new, but the car has been sitting for about three weeks, and was beginning to have starting problems due to colder weather, thus the glow plug change project.
The thing that baffles me is this glowing red conductor wire problem, coupled with the glow plug light remaining on a lot longer and then the light coming back on when the switch is turned all the way over to "start".
I will immediately use the manual pump and then attempt another start. As of awhile ago when I tried it again, it showed no sign of wanting to fire at all.
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Randall, from all these info that I got... this is what I would do first...
Glow plug, disconnect one glow plug wire... hook up one of the good old glow plug to that link and make sure you ground the glow plug to the engine... a battery booster cable will do. Turn on ignition and see if the glow plug glows... if yes, then go to the next glow plug and do it there. Make sure they all glows.
If all the glow plugs are determined to be good and working, then I would verify the fuel problem... .. if no bubbles... and fuel flow to the injectors are good, then I'd suspect valve job.
I know you had it 'professionally' done, but heck, professional doesn't mean a thing to me at all. Is that mechanic only specialize in MB? Does he work on older MB or newer one? I have ran into alot of new MB mechanic who has no idea what to do with the old one.
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I will start in on this immediately, as I am determined to exhaust all possibilities before sending the car out to the M-B shop, which is the only resource close by here.
There is only one flexible glow plug wire at the fuse/relay end of this (#1 cyl) system, and everything else is connected by the rigid serial connectors between the glow plugs. Still, I will check them again, although I have tested all new glow plugs and found them good.
The valves were set less than 1,500 miles ago by an old pro from Germany whom I've been having work on my Benzs for more than ten years and who definitely knows what he's doing, but nevertheless, at this point I wouldn't rule anything out.
Many thanks again, and I will report back any findings.
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Then have all the glow plug removed from the engine and hooke them all up... Make sure you don't short any of the wire to ground... a piece of wood will do. and with all of them hooked up, use jumper cable to ground two fo them at a time... one jumper jaw to each glow plug and the other end to a good ground point on engine and/or battery ground.
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OK, will do.
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snipped-for-privacy@mac.com ha scritto:

I'm just thinking aloud... Is it possibile that you're using old (i.e. resistive) lines between the glow plugs, instead of using the new (i.e. not-resistive) lines between them? AFAIK the modified 'fast' glow plugs need a new, isolated, flexible, cabling, instead of the old rigid one: check carefully the instructions contained in the kit. With some kits you also need to change the glow plug delay relais. Again, check instructions. Another point is that it's extremely easy to short glow plugs (this could be the explanation of the red wire phenomenon that you describe) by pulling too tightly the nuts. Carefully check the status of your new glow plugs: are they ok, or in short circuit? VERY CAREFULLY CHECK each single glow plug and each single connection (and insulator).

The only question mark here is if he has the right tools. To set valves it's better to use a special tool (a sort of fork key but with a deformated handle). And (it happens to pro's, too) sometimes a small carbon piece goes in between the valve and the seat. Thus, the valve seems correctly set, but it's not. Very common, with these engines...
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He bought the old type loop glow plugs rather than the new pencil type.
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I think I may give up today and get the new pin-type plugs. It doesn't look that difficult to wire those, and I have spent too many days on a simple problem. I should have done this when you first suggested it.
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Yeah I know... but ya know... some people have their own way that has to run their course for them to learn some thing.
Buy the kit... it is easier that way.
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Is there anything in the kit other than the plugs and the connector wires? I am now in a hurry to get this done and was thinking of just making the wires up here in the shop.
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Yeah, it also comes with new relay. The complete package.
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Tiger ha scritto:

Oh... ok. :-)
So: the torque should be: 20 Nm for the glow plug 3.5 Nm for the contact.
It's extremely easy to screw up the plug in the insulator, shorting it. So, it's a good idea to use a torque-controlled key. Maybe that's what happened. Randall doesn't need this info, now (his glow pugs are probably already damaged, now) but this is for future reference, whoever will be reading us in the future.
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