77 300 D glow plug head scratcher
 

Hi everyone,

I am new to this board and i have a few questions. I recently purchased a 77 300 D with 109,000 miles.Here is the problem I am experiencing...

A few days ago we had temps down in the low 20s overnight. The next morning when I attempted to start the car it would'n't fire at all. I checked the resistor wires and found that I was getting heat from the 5th to the 3rd cyl. but nothing after that. The resistor wires between the #1 and #2 GPs were warm but not nearly as hot as the others. I pulled all the GPs and replaced them with new Bosch pin plugs, which were just like the ones I pulled out of it. After reconnecting the resistor wires and hooking everything back up, the wires between cyl. #5-4-3 turned red glowing hot and stll nothing between cyl. 1-2-3. Any suggestions and ideas about what would cause this? I wasn't sure how hot the reisitor wires should get so i was worried when it turned red hot. Any help is greatly appreciated.

If those glow plugs are in series (which I think you imply), you should have the loop type plugs in it (I think). The end should not look like a pencil but a loop of metal. But I don't understand how you could get the heavy wires attached to the pin type plugs. It's possible to upgrade that engine to the pin type, but it that is done, each plug should have a separate wire going to it and it should not be connected to the other plugs.

77 300 D glow plug head scratcher
 

I thought that the plugs were the wrong type as well. i called my friendly neighborhood dealer and gave them the VIN # and they told me that it took the pin type, not the loop type. Plus, the pin type is what was in it when i bought it and it started like a champ. Beats me.

I think the problem is as follows (I may be wrong): The loop type plugs are designed to work at a variety of voltages since the voltage drops as the current goes from plug to plug. So the number 1 plug (nearest the radiator) gets a lot less voltage than the #5.
The pin type are designed to work at 12 volts. So the first few are working because they are at 12 volts or pretty close. The latter ones are not working because the voltage has dropped too low in the series wiring for them to function.

I'd put the loop type plugs in and see what happens, or get the kit that allows you to rewire with the appropriate electronics to put the pin type in.

You have a grounded glow plug at cylinder #3. Remove plug and use a wire brush to get as much carbon out as you can, then crank engine with the glow plug out to blow out the loose carbon.

With series plugs, a ground somewhere it shouldn't be will cause the rest of the plugs to fail to heat, and it will both cause hard starts and burn out the rest of the plugs.

You may also want to pull the #3 injector and check to make sure the ball pin hasn't broken and fallen down in the pre-chamber -- this will both short the glowplug and cause serious injector knock. Requires removal of the pre-chamber to fix.

Peter

Are there pin type series plugs??

I think there are, check on FastLane for the older diesels. They don't list loop type plugs, just pencil. They have the large base and the correct configuration for the wires.

Peter

I only see loop type with the large base for 77's. The pin type listed have the small base and it looks like they have less threads for the electrical connections.

Kerry:

Take a look at the conversion kit -- it has a relay, a new keyswitch, and large base glowplugs.

Peter

The electrical connection end of those plugs looks more like the parallel plugs than the series. I have been assuming that this upgrade involved changing the wiring to a parallel set-up. It doesn;t say anything about it in the description of the conversion kit.

If that is the case, using the wires from the series plugs could result in no current to the front ones from excessive resistance in the links.

Peter

I just picked up the Bosch upgrade kit for my 71 220D, from series to parallel. Each glow plug DOES connect from one to the next with a common wire, not an individual wire going from the relay to each plug. I haven't installed the kit yet (that's for this weekend).

I am dissapointed that they tell you its a kit that includes everything you need, but you also have to get a 6mm line to run from the relay to the battery, a 6mm line to run from the relay to the lead glow plug, and come up with a way to connect these lines to the relay (found some nuts and washers at a hardware store).

The box promises 3-7 second glows and after glowing. Sure beats the 60 second ritual I have with my series plugs every morning.

Eric

Cliff SCCA and everyone else:

Join us on this related thread over in the diesel discussion. We are all (unsuccessfully) trying to make sense of your system. Perhaps you can post a picture of what you have.


http://www.peachparts.com/shopforum/diesel-discussion/81781-kinds-glow-plugs.html#post524714