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'79 300SD not starting in 40° weather

Started by citymunky, 29 March 2010, 08:14 PM

citymunky

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.
[COLOR="Red"]http://www.dieselgiant.com/glowplugrepair.htm[/COLOR]

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.

[COLOR="#ff0000"]http://handbook.w116.org/ETM_78_3d.htm[/COLOR]/ 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:


Big_Richard

is the car stored in a garage or outside ?

in cold climates such as yours a diesel would benefit greatly from the installation of a block heater. If your driving the car everyday i would have it connected to a timer so the block is warm and the engine starts instantly when your ready to leave in the morning. Generic ones must be on the shelf in that part of the world.

s class

OK, being from a metric based country, I assumed that 40 deg meant celcius, but I realise now you mean farenheit.

I have never owned a diesel, but my understanding is that for operation, you need :

a) adequate fuel supply
b) adequate air supply
c) adequate cylinder compression
d) adequate cylinder temperature.

If one of these is under spec, the engine will probably still run, but will be difficult to start.

as to a), check fuel delivery rates.  The next possible issue is internal leakage in the injection pump.  Once the engine is running, fuel delivery may be sufficient to overcome any internal leakage.  But when shut off, if there is internal leakage, pressure on the injectors drains away. 

b) Is there a throttle valve in a diesel?  check for obstructions

c) This is an important one, because a diesel engine is a compression-ignition system.  Weak compression is what eventually sidelines high mileage diesels often.  If you haven't recently checked compression, it may be worth while.

d) When the engine is running, the heat produced by combustion is sufficient to sustain the required heat.  At start-up, one relies on the glow plugs to achieve this.  So yes, they need to be fully functional.  As MT correctly points out, a block pre-heater would greatly ease the task of the glow plugs.


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

wbrian63

40deg F should be a walk in the park for a properly configured MB diesel, even an older one with lower compression.

"I think" the glow plug light should stay on for the entire glow cycle. Does it stay on briefly and then go out, or does it stay on for the duration of the glow cycle?

Your debugging indicates you're getting voltage to the glowplugs for 30 seconds, which I think is the right interval.

You might try more than one glow cycle.

I don't know about W116 diesels, but some older MB's used serial connections to power the glow plugs. Voltage fed the first plug, which in turn fed the second plug, which in turn fed the 3rd plug, etc. The draw each plug reduces the voltage available to the next plug down the line and lengthens the amount of time for all the plugs to get up to temp. There's a "kit" available to convert serial plug setups to parallel, where all plugs get full voltage at the same time. As I understand it, this is a far better setup.

Also - folks here are some of the nicest in the world, but many of them are Aussies - and the W116 diesel cars were never available for sale in AU, so their experience may be limited.

I'd suggest posting your issues to PeachParts.com (used to be MercedesShop.com). There's an entire section dedicated to MB diesels, and if those guys can't help you with your problem, your car's not fixable.
W. Brian Fogarty

'12 S550 (W221)
'76 450SEL 6.9 Euro #521
'02 S55 AMG (W220) - sold
'76 450SEL 6.9 Euro #1164 - parted out

"Bond reflected that good Americans were fine people, and most of them seemed to come from Texas..." Casino Royale, Chapter V

citymunky

Quote from: Major Tom on 30 March 2010, 04:29 AM
is the car stored in a garage or outside ?

in cold climates such as yours a diesel would benefit greatly from the installation of a block heater. If your driving the car everyday i would have it connected to a timer so the block is warm and the engine starts instantly when your ready to leave in the morning. Generic ones must be on the shelf in that part of the world.

I park it outside, I live in a apartment complex. I did picking up a coolant heat, but I have yet to install it. I have a OEM block heater, but it doesn't work.


Quote from: s class on 30 March 2010, 05:23 AM


a), check fuel delivery rates.  The next possible issue is internal leakage in the injection pump.  Once the engine is running, fuel delivery may be sufficient to overcome any internal leakage.  But when shut off, if there is internal leakage, pressure on the injectors drains away. 

b) Is there a throttle valve in a diesel?  check for obstructions

c) This is an important one, because a diesel engine is a compression-ignition system.  Weak compression is what eventually sidelines high mileage diesels often.  If you haven't recently checked compression, it may be worth while.

d) When the engine is running, the heat produced by combustion is sufficient to sustain the required heat.  At start-up, one relies on the glow plugs to achieve this.  So yes, they need to be fully functional.

a) fuel delivery rates are fine, I learned that the hard way when I did the fuel system purge.
b)There is no Thottle Body on diesel
c)I never did a compression test on this car yet, so I don't know
d)When the engine is running yes, on cold mornings no.

Quote from: wbrian63 on 30 March 2010, 08:39 AM

"I think" the glow plug light should stay on for the entire glow cycle. Does it stay on briefly and then go out, or does it stay on for the duration of the glow cycle?

You might try more than one glow cycle.

I don't know about W116 diesels, but some older MB's used serial connections to power the glow plugs. Voltage fed the first plug, which in turn fed the second plug, which in turn fed the 3rd plug, etc. The draw each plug reduces the voltage available to the next plug down the line and lengthens the amount of time for all the plugs to get up to temp. There's a "kit" available to convert serial plug setups to parallel, where all plugs get full voltage at the same time. As I understand it, this is a far better setup.

Also - folks here are some of the nicest in the world, but many of them are Aussies - and the W116 diesel cars were never available for sale in AU, so their experience may be limited.

I'd suggest posting your issues to PeachParts.com (used to be MercedesShop.com). There's an entire section dedicated to MB diesels, and if those guys can't help you with your problem, your car's not fixable.

Your are right the glow light light should stay on the whole glow cycle but it doesn't. I do try more than one cycle, but that doesn't help. The older style glow plug system used loop-style glow plugs and they did run in serial.  My 300SD uses the newer style pencil glow plugs that run in parallel.

Also I guess you are right about most people on this broad being from AU, I'll post up on PeachParts

Thanks for all the replies.

citymunky

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.

Everything I check is testing good, but that car don't start in cold weather.

kru0042

Sir,

I have two W123 Diesels, and a W115 diesel. I drive my 85 300D turbo Diesel everyday in Calgary year round, and as you probably know we get some really cold weather here. As mentioned, a good, functioning block heater is indispensible. I actually have this and a magnetic heater which clings on to the oil pan which I put into service for temperatures below -15 Celcius. This gizmo is actually designed to keep cattle troughs from freezing in our arctic conditions.  Any colder than that, and I place a car cover around the entire from third of the car and run a space heater under there. She will start in -35 degrees.

Does the car start when it is warm outside? Also ensure that you have purged the air out of the fuel system. There is a handy plastic purging pump on your engine next to the injection pump. You could also check to ensure that your injection pump is functioning properly. I assume your fuel filters are clear. I also swear by the stuff on Diesel Giant. Russ is the Man!!  Did you do a Lubro Moly purge? This alone can dramatically improve your engine performance. There is excellent diesel specific information on the Benz World forum as well. You might want to check this out.

I know how frustrating it can be to start diesels. You have covered all the most important bases. I bought my daily driver from a professor who loved the car, but gave up on it out of exasperation with it not starting. Failing all these, you might have to break down and take her to  a good diesel engine specialist in your city.

Best of luck!!

Super Einspritz Lang

Jimbo

First off I hope that you are using Bosh GP's in your diesel, other cheap brand's may brake off inside the engine, my 300sd GP light will not turn on if there is 2 or more bad GP's in there,
although if I cycle the glow plugs the light will come on but not as long as it should and the car will not start in weather under about 50 deg.

How old are your GP's ?