W116.120/OM617


So a problem I had since day one was getting my car started in cold weather. Two months of owning this 300SD, and I'm tried of fighting with the car to get it started. At first I thought is was the used battery, so I replaced it was a Rep-top Optima battery (800CCA). For that first week or too starting the car was not such a problem. Soon afterwards start up got harder and harder. I would turn the key and the glow plug light will turn on than off. I'll crank and crank and crank and after 10 minutes or so the car will start. (One time it took 40 minutes) Than goes all the white smoke and rough idle.

To Date maintenance done by me includes
-Oil Change and filter
-Fuel System Purge
-Replaced both fuel filters
-Valve Adjustment
-Replaced all the old fuses
-Replaced the Battery
-Replaced the Alternator

I fould a DIY on DieselGiant.com for glow plug repair, but I still can't figure out what is wrong with my car because everything I checked was good.
[URL="http://www.dieselgiant.com/glowplugrepair.htm"][COLOR="Red"]http://www.dieselgiant.com/glowplugrepair.htm[/COLOR][/URL]

1)I have 13.09 Volts off the Batt. with the car off.
2)Sockets 1, 2, 3, 5, & 7 read 0.6 Ohms.

3)I have 13.09 Volts coming into the relay.
4)I have 13.09 Volts on both sides of the 80 Amp fuse.
5)When the key is turned I have 13.09 Volts in pins 1, 2, 3, 5, & 7 for 30 seconds.

[URL="http://handbook.w116.org/ETM_78_3d.htm"][COLOR="#ff0000"]http://handbook.w116.org/ETM_78_3d.htm[/COLOR][/URL]/ Click Wiring Diagram--> Than look at Pg 19.

However Socket 6 which goes to the Coolant temp sensor reads 10.07 K Ohms, and socket 8 which goes to the Preglow Ind Temp sensor reads 4.5 K Ohms. Also the coolant temp gauge in the dash never worked as far as I had the car.

I'm loss:confused:


Also Does anybody know which sensor is "A" and whick sensor is "B"?
-"A" is between GlowPlug 1 and GlowPlug 2.
-"B" is between GlowPlug 2 and GLowPlug 3.

Somebody on a different forum suggested I measure the voltage at the glow plugs when the relay is engaged. Positive lead on the glow plug, negative lead grounded to the block, and expect to see something in the neighborhood of 10v-10.5v. If the measure anything near full battery voltage then the plug is not drawing sufficient current to glow properly.

Ok, I did that and here is what I got.

With the Battery voltage at 12.24 Volts, I turn the key and I got 10.4 Volts at each glow plug. I let the relay stay on for full 30 seconds. That should mean the glow plugs are good, but I'll do the test again. This time the battery voltage was drained down to 11.95 Volts. I turned the key and I got 10.16 Volts at each glow plug, so again the glow plugs are testing good.

I start up the car to charge the battery for my next test. (Yes I said started, in the afternoon the temp was 67°F). After I was done charging, I tested all the pins on glow plug time relay again. Battery voltage was 12.7 volts, the glow plug pins 1,2,3,5, and 7 were reading 12.5 volts. The coolant temp sensor Pin 6 was reading 7.41 volts, and the Preglow Ind Temp Sender was reading 4.16 volts. The thing is I don't know if the reading off of pins 6 and 8 are normal. With that being said, I removed the #1 glow plug from the cylinder head to test it using 12 volts direct. What do you know, it was cherry red within 2 seconds, which again means the glowplug is good. Also the glowplug was made by Bosch.

I'm so loss on why the car is so hard to start in the cold.

How much blowby does it have?
A is for the relay and B is for the gauge.

(03-30-2010 10:03 PM)ForcedInduction Wrote:  How much blowby does it have?
A is for the relay and B is for the gauge.

I have a lot of blow-by, but what does that mean? And thanks for the info about the Sensors, that's what I thought but wasn't sure.

Again, starter motor and connection between negative battery terminal.

Sorry, kind of off topic, but what if there is no "A" sensor?

A is for old glowplug relays that use engine coolant to control glow time. Post 1980 the relay uses ambient air temp instead.

i had the same problem it could be similar to this..... i bought monark glowplugs thinking they were the best and when the cold weather hit my car had a very hard time starting and i went crazy replacing things.


remove your glowplugs and test them. get a pair of jumper cables attach them to the battery then put the negative on the glowplug middle section and the postive on the bottom part... if it doesnt glow red the plugs are bad.


ream the holes to get red of carbon depoist with a small wire brush for the holes and only purchase BOSCH plugs.




But since your now parting out the car it doesnt matter... waitng for those regulators and windsheild