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.
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?
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
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.
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.
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.
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.
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...
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
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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