240D Glow Plugs Mystery
 

I have a 1980 Mercedes 240D. About two months ago the glow plug light went out. I knew there had been a problem since the glow plug light would flash every time the car started. I've replaced the glow plugs, the relay, and the car battery (which was really old and needed to be replaced anyway). No change. When I turn the key in the ignition, it wants to start up, but I can't get it to turn over without the glow plugs. I've tried starting it in neutral as well, but the response is the same- no glow plug light at the dash. I'm stumped. Can anyone give me some pointers on what to check next? I'm trying to avoid a costly trip to the mechanic if it's possible.

Thanks

RE: 240D Glow Plugs Mystery
 

It sounds to me like the relay is bad. Are you certain it's pluged in correctly. Also follow the "hot" wire feeding the relay and check for power.

There is a procedure for testing the relay, don't have it here but can check for you tomorrow. You will need a multi-meter.

RE: 240D Glow Plugs Mystery
 

I've already replaced the relay with a new one- could the wiring harness itself go bad? Do harnesses do that? Is there way I could test the tempature sender? I think there's two of those in the engine- I wondered what they were- I noticed them when I changed the glow plugs, but had no idea they were temp senders. Do those go bad after 28 years ? Thanks

RE: 240D Glow Plugs Mystery
 

To test the temperature senders all you have to do is remove them, measure the starting resistance, heat a pot of water and check the temperature with an appropriate thermometer. When the temperature hits 175-190F set the probe end of the sensor in the water with the ohmmeter attached. You should get a resistance change. If not, the sensor is bad.

RE: 240D Glow Plugs Mystery
 

This may be redundant, but I re-read the origional thread again.

"When I turn the key in the ignition, it wants to start up, but I can't get it to turn over without the glow plugs. I've tried starting it in neutral as well, but the response is the same- no glow plug light at the dash."

Does the engine turn over at all, ie/ is the starter motor working? Somewhat confusing in discription...Perhaps an all together different problem lost in translation?

RE: 240D Glow Plugs Mystery
 

The starter motor is working. If I try to start the engine even though the glow plug light never comes on, the starter cranks, but the engine will not "turn over". I followed the glow plug diagnostics on DieselGiant's website and everything passes. I also jumped the battery while attempting to start, in case the new battery had been drained by the testing- no glow plug light, but I could crank the starter all day long.

I guess the compression in my car is not good enough to start without hot glow plugs. I've contemplated (besides putting the car on eBay) either getting a relay bypass kit or bundling a bunch of wire together and attaching directly from the battery to the glow plugs just to heat them up, to see if the car will start. The relay's new and passes the voltage tests, and the wiring harness passes the resistance tests. The only thing I have yet to check is the temp sensors since I have to drain the radiator to do get them out. Do the temp sensors really affect the glow plug relay? I don't understand the role they play in getting the car to start. Thanks for the advice.

RE: 240D Glow Plugs Mystery
 

if the engine is not turning over then new battery will cure it

I managed to start my 200D when it was -5 with no glow plugs! (it took 10 minuts and lots of smoke.
once it is turning hot wire the glow plugs direct to the battery be carefull 60 amps then it will start

RE: 240D Glow Plugs Mystery
 

I also found that every two years the Valves needed re adjusting it is only a 1 hour job

or the compression would fall
i had my old 200d for17 years and it always got me home