'70 220D with stock Bosch GP's, replaced 1K miles ago, reamed, months old Bosch group 49 battery.
Was running fine, no issues. Parked it a week ago, and went to start this
past Friday. No glow at the salt shaker. Turns over fine. Pulled plugs look good, continuity checked OK. Disconnected power wire to GP's at cylinder #4,
pulled gorilla knob and voltage measured at 12.4 volts. Continuity ok from one plug to next one.

Any suggestions appreciated.

Thanks,
Warren

When one Plug goes bad all of them stop working because they are in series. That means that the Glow Plugs are not grounded through the Glow Plug body to the Cylinder head.

The front most Glow Plug has a Ground wire likely goes directly to the Cylinder Head. Disconnect the Wire from the Head and connect your Voltmeter in series. Have someone pull the Knob into the Glow Plugs on position and see if you get Voltage. If the Plugs are working you will get Voltage but it will be less then 12 Volts.

If you get no voltage one or more of the Glow Plugs is no good.

In the pic the burned loop is typically what happens. Things not right in the Pre-combustion chamber like worn Injectors or Injection Pump timing off can cause that. But, I would say worn Injectors are the most frequent cause as the spray can often hit the Wire Loop and it cuts right thorug it.

The other common isue is Carbon can build up on the inside and cause a short circuit.

If you want to test the individual Plugs you need to remove the Wires. The Pic shows you were to probe with your Ohm Meter. I don't know what Ohms is good or bad but you are likly facing a burned loop so there would be infinite Ohms.

The official method is in the drawing in post #4 1976 300D Glow plug circuit issues.
The Voltage starts off at X amount at the Fire Wall and as it passes through each Glow Plug each plug uses up about 0.75- 1.25 Volts and that means as you progress frontwards there is a voltage drop after the current goes through each plug.

The individual Glow Plugs cannot take a full 12 Volts; it will quickly burn the loope. If you remove the Wires besure to take a picture or draw where they came from so they get back in the same place.

Someone is likely to say you should convert to the Adapter Type Pencil Glow Plugs. If you do that you cannot use the very front Ground Wire as the Adapter Plugs are grounded through the outer Body and the Cylinder Head. Also there is no zig-zag resistance wires in that setup.
Also try to find a thread on the above that has your year and model and besure you are able to use the Adapter Glow Plugs in your's.

Attached Thumbnails

 

__________________
84 300D, 82 Volvo 244Gl Diesel

Look at your glow plug relay.
Is it a bit warped? replace it.
If that does not help, maybe your glow plug relay is funky.
Make sure that your chassis ground strap is clean.

"Disconnected power wire to GP's at cylinder #4,
pulled gorilla knob and voltage measured at 12.4 volts. Continuity ok from one plug to next one. "

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

There also is a fuse link. Possibly on the engine firewall on your car. Where are you reading the twelve volts at?

There is no relay on the original set-up of the W115-220D.

There is no fuse in the original set-up of the W115-220D.

Before you put it all together, I would recommend you clean all the parts with a wire brush at all the contacts.

My 220d would sometimes lose contact between the jumper wires (the wiggly metal things) and the GPs. I could get a circuit again by simply tightening one of the GPs nuts. But to make the problem go away longer term, I had to take it all apart, wire brush it, and then reinstall. I also used some ox-gard electrical grease at each contact, but that was probably unnecessary.

The GPs heated up a lot faster after the cleaning, so that was a nice side-benefit.

__________________
1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

OK I meant to write "strip fuse" but you don't have one anyway. good luck

w115 glowplug system?

220d glow plug problem

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD