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  #1  
Old 03-06-2007, 02:37 PM
Sam
 
Join Date: Nov 2005
Location: North Georgia
Posts: 86
Need Help with Glow Plug retrofit on '76 300D "W115"

I bought this kit from Russell at Deisel Giant. It included five pencil style glow plugs, connecting wires, and a bar fuse. Being that this is a w115 chassis 300D, a number of things are different than the much more common w123 chassis 300D. Most notable is the grounding method. The 115 cars do not have the braided strap grounding the series. The sensor that is threaded into the block has, of course, the sensor wire plugged into it that I assume terminates at the relay under the steering column. It also has a thicker black wire that was originnaly attached to the front-most glow plug. I guess that this was the original ground for the system.

The problem I have is this. The plugs get no voltage when the key is turned to the run position. If I jump the 5 and 6 pin at the relay, they get hot immediately. Russell has told me that the thick black wire at the sensor needs to see 12V in order for the system to function. I tried this once and got a fireworks show. I fused the jumper wire so no damage was done but obviously this is not correct. Russell has not worked with the W115 300D so he does not know for sure what to do.

I know this has been done before and I've searched until my eyes hurt but the exact answer still eludes me. I could just wire a switch at the relay plug between 5 and 6 but I want a more elegant solution......I want it done right.

Can some wise soul point me in the right direction? I need this thing buttoned up very quickly.

Thanks,

Sam

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  #2  
Old 03-06-2007, 02:59 PM
rrgrassi's Avatar
mmmmmm Diesel...
 
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Check all of your fuses again. Also do you know which wire from the ignition switch activates the relay?
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70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K
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  #3  
Old 03-06-2007, 03:32 PM
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Does your car have the older pull starter/ glow plug switch on the dash? I'm assuming you're going from the older loop style setup in which case they do have a ground strap on the front most plug as they are wired in series. The black wire coming off the firewall is for power, almost sounds like you have it backwards. I just did this conversion to a '75 240D and it should be pretty painless, unless you short something out in the process.
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  #4  
Old 03-06-2007, 04:15 PM
KylePavao's Avatar
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Join Date: Jan 2005
Location: Tiverton Rhode Island/University of Rhode Island
Posts: 400
Same problem

I had the same problem. I don't believe the relay in the W115 can handle the voltage of the bosch duraterm plugs...I had 3 plugs working in the block, but number 4 would always draw too much voltage. My father had an EE work the circuit out, and I really don't think the relay can support that amount of voltage reliably.

Regards,
Kyle
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1976 300D
190,000 Miles
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  #5  
Old 03-06-2007, 04:34 PM
rrgrassi's Avatar
mmmmmm Diesel...
 
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Your kit should have included a new relay as well.
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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K
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  #6  
Old 03-06-2007, 04:40 PM
Sam
 
Join Date: Nov 2005
Location: North Georgia
Posts: 86
No Gorilla knob on a 300D w115

The 240D still had them I seem to recall but the 300 had a regular key setup.

There is no dedicated glow plug fuse and all the others are in fine shape. Any one of them with even a hint of discoloration has been replaced in the last two days.

jfields. You are correct. The black wire coming from the firewall is to power the plugs. I'm not too concerned with this one because I can make it hot by jumping pins 5 & 6 at the relay (per manual). I have no doubt in the fact that this wire is properly connected. There is no braided ground strap, however. Erase all that wonderful w123 knowledge. This system uses about a ten gauge, black wire that runs directly from the sensor threaded into the block. I can only assume it serves as a ground but it also must trip something in the sensor to allow the plugs to see 12v.

If I bypass the sensor by jumping pins 5 & 6 it works perfectly.

rrgrassi. I have not traced the wire that runs from the ignition switch to the relay. I can hear/feel it energize and I've switched it out with a known good one and nothing changes.

This thicker black wire running from the sensor was originally bolted to the front-most glow plug on the old series setup. I imagine that this sensor lead needs to see something in order for the system to work properly. I've tried grounding it with no effect. I've even tried Russell's advice by introducing 12 fused volts. This had an effect but not a desirable one.

I'm stuck. If I just knew the complete function of this errant wire, I'm sure a solution would be close behind. Could be wrong here, though.

Thanks for the replies and keep 'em coming. I've got to get this done one way or the other by Friday.

Sam
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  #7  
Old 03-06-2007, 04:52 PM
Sam
 
Join Date: Nov 2005
Location: North Georgia
Posts: 86
More replies so fast? I'm a slow typer.

The kit did not come with a new relay. The seller claims that it is not necessary. If the relay was not capable of sustaining the required current, I still think I would see some voltage spill out to the plugs for as long as the relay could stand it. There is not even an instantaneous voltage spike when the relay is energized. I know just enough about circuitry to get myself fried so what do I know, though?

Kyle. This new relay....is it plug and play or is wiring modification necessary? Is there a part number I can reference? I don't mind spending the cash to get one but I need it in about a day.

Any more ideas before I try a new relay?

Thanks,

Sam
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  #8  
Old 03-06-2007, 05:06 PM
rrgrassi's Avatar
mmmmmm Diesel...
 
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I believe brown wires lead to ground on the MB. Black and other colors should supply current. Have you tested for voltage one the errant black wire, or do a continuty check to ground?

It's difficult to erase 123 knowledge when that is all I have.
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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K
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  #9  
Old 03-06-2007, 05:07 PM
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My kit did come with a new relay but I found no need to use it on a 77 123.
Doesn't that sensor determine the amount of time the glow plugs stay energized based on the temperature of the block? Can you test the resistance through the sensor?
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1984 300SD 315k--daughter's car
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  #10  
Old 03-06-2007, 08:26 PM
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Quote:
Originally Posted by samdon View Post
Most notable is the grounding method. The 115 cars do not have the braided strap grounding the series.
They must have had a ground return. Use a DMM to measure the resistance to GND (Chassis) on the black wire that was connected to the front glow plug. This would never see 12V (as you were told) in the series style system unless you had an open plug (there is a voltage drop across each plug and resistive wire). I can't understand why the final plug in series would be connected to a temp sensor...

You should have 12V on pins 3 (when cranking) and 4 (ignition on) at the relay. Pin 1 should be GND (check resistance to GND w/DMM). Pin 2 should be the 'temp sensor'. Pin 5 = B+, pin 6 = GP output, and pin 7 = Lamp control.
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  #11  
Old 03-07-2007, 11:23 AM
Sam
 
Join Date: Nov 2005
Location: North Georgia
Posts: 86
Will check resistance this afternoon.

rrgrassi. The "w123 knowledge" comment was a veiled joke probably lost on everyone but myself. There is such a huge base of info on the 123 and almost nothing on the late 115 300D's. I've never owned a 123 diesel but I've been dealt enough emphatic advice pertaining to those cars that I'd bet I know more about them than about my own Miss Margret (Sorry. Wife named the car)

Thanks for the pin designations, pdxwaker. I will check ground resistance at the mystery wire as well as pin 1 at the relay plug this afternoon.

I'm going to throw out a WAG. Don't confuse this with an EWAG. I'm simply not capable when dealing with electrical issues. If the relay itself is not timed -and I'm not sure it is looking at the diagram - this wire must offer some bit of info to the the sensor/switch rather than simply serving as a ground. Does it possibly deliver voltage flux to the sensor which in turn de-energizes the relay based on prescribed values? I remember with the old series setup, the glow time was never constant. If it was relatively warm outside it would glow for a much shorter period of time - On a cold morning it might go for a good long period. What is the difference in voltage drop between the last plug in the old series and any one of the new parallel plugs? Should the wire possibly be connected as it was? I can't see this being the case as I know for a fact that it is not looking for battery voltage but how about the slightly lower, but climbing voltage seen at the plugs?

Thanks for all the ideas. Keep them flowing as it's obvious even to me, by reading the above, that I don't have a clue.

Sam
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  #12  
Old 03-07-2007, 11:34 AM
rrgrassi's Avatar
mmmmmm Diesel...
 
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My parallel system on my 123 does the same thing, the warmer the temp, the shorter the GP light is on.

Do you have the new GP's connected in parallel or in series? The pencil type plugs should not have a resistance wire running between them. I do know that on the newer relay types, each GP has it's own power wire and is grounded throught the block.

Forgive my ignorance, but what does WAG and EWAG stand for?

Miss Margaret is not a bad name for a car. Could be much worse.
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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K
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  #13  
Old 03-07-2007, 12:00 PM
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Quote:
Originally Posted by samdon View Post
I remember with the old series setup, the glow time was never constant. If it was relatively warm outside it would glow for a much shorter period of time - On a cold morning it might go for a good long period. What is the difference in voltage drop between the last plug in the old series and any one of the new parallel plugs? Should the wire possibly be connected as it was? I can't see this being the case as I know for a fact that it is not looking for battery voltage but how about the slightly lower, but climbing voltage seen at the plugs?
There should be an internal timer in the relay that prevents the plugs from cycling more than ~110 sec. I'm assuming this is used in conjunction with the temp sensor in the block (though I'm not certain because the online service manuals are down). If the temp sensor was truly connected to the last plug in series (toward the front of the car), it must have had some serious current flowing through it (~50A).

My guess is that the temp sensor is used only for the GP indicator light. For W123s, the glow plug light will go out but the plugs are still cycling. The GP light can be used as a 'ready to start' indicator. I know this isn't a W123 but your GP relay system was the predecesor to the W123...

Do you know if your replacement plugs are Bosch Duratherm? If so there shouldn't be a problem with forcing the 110 second max cycle time. Note that this cycle time can be shortened by just cranking the engine earlier (this is why there is a 'cranking' input on the relay... glow plug power is cut off when cranking). I would suggest grounding the temp sensor input to the relay and just forcing the max glow plug cycle time. Use your DMM and a stop watch to verify that the max cycle time is ~110 sec. It would also be good the verify that plug power is cut off when cranking starts.

Don't let this change worry you... all the older style W115 systems (non-relay) were completely manual... glow plug cycling time controlled by how long you pull the start knob. Essentially you'll be taking the 'auto temp' shutoff out of the control loop and creating more of a manual style control.

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Last edited by pdxwaker; 03-07-2007 at 12:13 PM.
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