115 Diesel Question

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115 Diesel Question

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115 Diesel Question - 2/8/2007 8:36:42 PM

phylarch

Posts: 3
Joined: 2/8/2007
Status: offline

I updated my 1976 300D glow plugs to the pencil type wired in parallel. Now my GP indicator light wont come on, but it does light up when I turn the motor over. Go figure!
I didnt connect the ground wire formerly connected to old GP 1, I believe its a ground wire, don't know, its connected to a temp. sensor in the block. It also has no voltage.
I think I might have blown the GP fuse, but I cant find it. Where is it on a 115? The wire formerly conected to old GP 5 is now connected to new GP 5, but It carries no voltage at all, I checked it with a meter.

Has anyone upgraded a 300D to new style glow plugs? Am I missing something?

Any help would be appreciated, thanks,
Ben
1976 MB 300D, 115.114, 617.910

Post #: 1

RE: 115 Diesel Question - 2/9/2007 12:56:44 AM

otm646

Posts: 63
Joined: 11/21/2006
Status: offline

the ground wire you spoke of is not needed as the motor is grounded to the frame via the transmission.
the temp sensor determines if the plugs need to be warmed. it is a thermistor, which is to say that as the sensors temperature changes the resistance of the sensor changes with it.

there is no fuseable link between the plugs and the glow relay on the 75-76 300D

there could be a few ways your are getting an intermittent glow light.
1.you could have a poor transmission to frame ground which only works when the vibration from the cranking motor cause an intermittent connection
2.you could have the same issue with the ground wire for the glow relay

if none of these are to blame you might have a loose ground on the instrument panel which causes the bulb to light. an easy check is tog et a 12volt light and attach the ground to the battery and the positive terminal to the positive wire leading to the glow plugs. if the light operates while you are cranking the engine you know the instrument panel is not you cause.

renew all of your grounds!

76' 300d @460k

(in reply to phylarch)

Post #: 2

RE: 115 Diesel Question - 2/9/2007 11:25:08 AM

phylarch

Posts: 3
Joined: 2/8/2007
Status: offline

Thanks a ton, you've been a great help.
Where does that sensor wire (coming off the thermosensor, formerly connected to glow plug 1) go. Do I need to ground it also? Remove it?

I think your right for another reason, I moved my battery to the trunk, and didn't use the exact same ground location, I moved it about 8 inches. My corroded batt tray wouldnt hold the big batt, so i moved it to trunk with heavy 4gauge welding lead. I'll renew my grounds today.
Thanks again,
Ben
Phylarch@hotmail.com

< Message edited by phylarch -- 2/9/2007 12:27:00 PM >

(in reply to otm646)

Post #: 3

RE: 115 Diesel Question - 2/13/2007 1:35:20 AM

otm646

Posts: 63
Joined: 11/21/2006
Status: offline

i think i may have confusd you a little bit so let me clarify.

the sensor which tells the relay if it needs to turn on is a small black wire with a connector that fits over the connection pin protruding from the sensor. the conection is the same style as the other tempature sensor on the thermostat manifold. there are two of these temp sensors on the block.

now the wire which was connected to plug one (closest to the firewall) needs to get reinstalled to its location on plug one. that wire provides the power to the plugs. now in that connection there are actual two wires. one is power from the relay, the other one with the purple stripe is the lead which provides power to the glow indicator in the dash.

that must be some battery. i have a 1000cranking amp/850 cold cranking amp battery that fits just wonderfully in the stock tray. why did you feel you needed a larger battey?

with that battery i jumpstarted a dodge 3500 no problem. it was hopeless they were trying to start it with a geo in 8 below weather, i should have taken a picture

(in reply to phylarch)

Post #: 4

RE: 115 Diesel Question - 2/17/2007 6:18:50 PM

phylarch

Posts: 3
Joined: 2/8/2007
Status: offline

Thanks again OTM646
I have an Optima Red Top 1000cca/800ca. Its not big at all, but the tray under the hood was very rusty and corroded, so i relocated the batt to the trunk.

The car origianlly had the glow plugs wired in series (factory) Three of the old plugs were bad (infinite ohms) So i decided to upgrade to new pencil type plugs and wire them in parallel as instructed
On the factory wiring (series) Plug 5 (closest to radiator) had a wire going to the sensor between plug 5 and 4. I have no idea were to put this wire now.

I can trick the sensor into feeding the plugs power by diconnecting plug 5. My glow plug sensor light will then come on, then i reattach plug 5. glow plug sensor light stays on, and then the car cranks beautifully.

Oh yeh, I checked comppression today and all 5 cylinders were within 280-300 psi. Is this great, good, average or bad? Im still trying to decide if i want to restore the car and make a daily driver. What do you think?

(in reply to otm646)

Post #: 5