'79 300SD not starting in 40° weather - PeachParts Mercedes-Benz Forum

citymunky · #1 03-30-2010, 03:35 PM

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.
http://www.dieselgiant.com/glowplugrepair.htm

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.

http://handbook.w116.org/ETM_78_3d.htm/ 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

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.

barry123400 · #2 03-30-2010, 04:33 PM

Well either you have no fuel at the time of attempted startup or the glow plugs are not really functional. Try the glow plugs first. They are the more usual culprit.

Read the voltage actually present at one of the glow plugs during the dash light glow plug interval . Under proper load the voltage should sag down to about 11 volts if the plugs are drawing some current. This may take two bodies to accomplish. There may be little or no voltage present is going to be a possibility as well.

In otherwords it is a process of one thing at a time. None of them really hard to do. Also check each plug separatly for continuity. . It is quite possible you have low or no voltage at the plugs during the active cycle. Or you have some bad glow plugs. Either can usually be easily established by fairly easy testing. Members on site will give you guidance at interpreting what you report back with.

BoiseBenz · #3 03-30-2010, 04:42 PM

You may have a weak starter, too. Do you have access to other 617A engines to hear what "normal" cranking speed sounds like?

Ether · #4 03-30-2010, 08:10 PM

I offered this response to your post on Benzworld :

Your description of the starting troubles would seems to indicate a case of non functioning glow plugs. You need to measure the voltage at the glow plugs when the relay is engaged. Positive lead on the glow plug, negative lead grounded to the block.

You should expect to see something in the neighborhood of 10v-10.5v. If you measure anything near full battery voltage then the plug is not drawing sufficient current to glow properly

This is essentially the same direction Barry123400 is giving you above. From your description I'm not convinced you've eliminated the GP's as culprit. Check those voltages while the relay is engaged and report your findings.

citymunky · #5 03-30-2010, 08:23 PM

Ok, I did what you suggested, 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.

Quote:

Originally Posted by BoiseBenz

You may have a weak starter, too. Do you have access to other 617A engines to hear what "normal" cranking speed sounds like?

I'm not 100% sure, but I think the starter in fine. Also I don't know a other soul who owns a 300SD.

Ether · #6 03-30-2010, 08:50 PM

Well, your glow plugs are certainly drawing current and those numbers seem about right. Are the other 4 plugs Bosch? Any chance you have some of the crappy Autolites in there?
Have you done a compression test?

Also, post your location. You may find a forum member nearby that can assist with your troubleshooting.

citymunky · #7 03-30-2010, 09:30 PM

Quote:

Originally Posted by Ether

Are the other 4 plugs Bosch? Any chance you have some of the crappy Autolites in there?
Have you done a compression test?

Also, post your location. You may find a forum member nearby that can assist with your troubleshooting.

I'll have to check tomorrow, and no on the compression test, I haven't had the time yet.

barry123400 · #8 03-30-2010, 10:33 PM

Okay this has been very frustrating for you. Glow plugs can still indicate as yours do and be tired. But lets forget about that for a awhile.. Lets do some general things instead. Have the valve clearances been checked to your knowledge? They can cause starting issues if far too tight. But other than that they should be checked for having reasonably accurate clearances every 15k.

Many of these old diesels have never had them checked in a dogs age. some probably because some owners never knew they did not have hydralic self adjusting lifters. Most though took the position if not broke do not fix. It is required periotic maintenance.

After that I would put a piece of clear hose on the return valve of the injection pump and submerge the end in a container. I would want to verify fuel is being pressurized enough to flow. If it appears to be so without a large air component in the observed clear fuel line when cranking. It passes the fuel availability test. There will be one last component to that test later.

Right now some general information is needed. At sixty five degrees does the engine catch and run smoothly after only rotating a time or two. Or is the startup still many turns of the engine? Just far far less than when at forty degrees.

Well you should do the valves first to get them out of the way. Read the archives about how if you do not know. These are an owner serviceable car.

It is important to know how to adjust the valves as a garage may charge you 100.00 each time. If you keep the car for a long time they will need checked many times. After the first time like many other things it is very easy to do. There has to be a first time. Or get a knowledgeable friend to assist.

What you are engaged on now is a learning and familiarization effort on your car. It will be culmulative in nature and save you money. You can ask for clarification of any item as you go along on site. Members will help. Some are very skilled. .

Personally I am interested mostly in your fuel supply. At forty degrees cranking and cranking until it starts indicated perhaps a lack of fuel or too much air at the time of attempted startup. This is not all that uncommon. Just masked a little at higher temperatures. Thats why the return line fuel test might indicate something is going on.

You can just remove the return line from the return valve on the injection pump and have someone crank the engine for about ten revolutions. You want to see fuel coming out that return valve right away. If there is then the clear hose test for air after the car has sat for awhile. Fuel could be draining back to the tank for example when the engine is off. Too much air is then getting in.

I also feel there is still a good chance the engines compression is okay as it will still start at 40 degrees if you keep cranking. The glow plug effect is gone after the first while so I would assume the engine starts whenever it gets the delayed fuel. Or clears the air in the fuel. The white smoke on startup can be caused by too much air in the fuel as well.

Normally with low compression the engine either catches right away or it may never start. The starter is no longer cranking as fast. You will have lost the glow plug assistance as well. Actually starting at forty degrees with no glow plug assistance is very good. Most will not do it. How many indicated miles on this car and do you think them an accurate representation?

This problem is well worth pursuing in my opinion and is or should be pretty cheap to locate . Other than your time of course.

You may as well check one more thing before coming back. With the engine running is there a stream of bubbles going through the small primary fuel filter? There should just be one static bubble in there not the bubble and at the same time a stream of air bubbles. Also look at the small hand primer pump. Does it have a white top? Or a black top? Is it wet with fuel?

leathermang · #9 03-30-2010, 11:07 PM

I have not read all the posts..
the FSM says to try leaving the gps on a minute... instead of the thirty seconds...
but I did see above about ' tired' gp's... pull them and ream the hole.. instructions in archives... they can be good but effectiveness blocked by carbon build up...

warmblood58 · #10 03-31-2010, 12:30 AM

Quote:

Originally Posted by citymunky

Ok, I did what you suggested, 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.

I'm not 100% sure, but I think the starter in fine. Also I don't know a other soul who owns a 300SD.

Forget voltage! Pull glowplugs and hook each one up to a battery and visually inspect. They should glow red hot within seconds. From the time you connect the battery leads, start counting. My car was starting to start slow and 3 of my five were weak/non functioning in spite of good voltage reports- Glows do wear out -

layback40 · #11 03-31-2010, 05:08 AM

X2 for removing GP's and bench testing them. If they dont glow then replace them. Too much importance is placed on measuring voltage & resistance. Visual testing will soon tell you if they are the problem.

fruitcakesa · #12 03-31-2010, 08:21 AM

My 240 had 3 out of 4 GP's no good and starting was a bear in cool weather. I was changing injectors at the time so I could see each GP in the hole.
New GP's = easy starts.

citymunky · #13 04-03-2010, 06:25 PM

Quote:

Originally Posted by barry123400

Okay this has been very frustrating for you. Glow plugs can still indicate as yours do and be tired. But lets forget about that for a awhile.. Lets do some general things instead. Have the valve clearances been checked to your knowledge? They can cause starting issues if far too tight. But other than that they should be checked for having reasonably accurate clearances every 15k.

After that I would put a piece of clear hose on the return valve of the injection pump and submerge the end in a container. I would want to verify fuel is being pressurized enough to flow. If it appears to be so without a large air component in the observed clear fuel line when cranking. It passes the fuel availability test. There will be one last component to that test later.

Right now some general information is needed. At sixty five degrees does the engine catch and run smoothly after only rotating a time or two. Or is the startup still many turns of the engine? Just far far less than when at forty degrees.

Personally I am interested mostly in your fuel supply. At forty degrees cranking and cranking until it starts indicated perhaps a lack of fuel or too much air at the time of attempted startup. This is not all that uncommon. Just masked a little at higher temperatures. Thats why the return line fuel test might indicate something is going on.

You can just remove the return line from the return valve on the injection pump and have someone crank the engine for about ten revolutions. You want to see fuel coming out that return valve right away. If there is then the clear hose test for air after the car has sat for awhile. Fuel could be draining back to the tank for example when the engine is off. Too much air is then getting in.

I also feel there is still a good chance the engines compression is okay as it will still start at 40 degrees if you keep cranking. The glow plug effect is gone after the first while so I would assume the engine starts whenever it gets the delayed fuel. Or clears the air in the fuel. The white smoke on startup can be caused by too much air in the fuel as well.

Normally with low compression the engine either catches right away or it may never start. The starter is no longer cranking as fast. You will have lost the glow plug assistance as well. Actually starting at forty degrees with no glow plug assistance is very good. Most will not do it. How many indicated miles on this car and do you think them an accurate representation?

This problem is well worth pursuing in my opinion and is or should be pretty cheap to locate . Other than your time of course.

You may as well check one more thing before coming back. With the engine running is there a stream of bubbles going through the small primary fuel filter? There should just be one static bubble in there not the bubble and at the same time a stream of air bubbles. Also look at the small hand primer pump. Does it have a white top? Or a black top? Is it wet with fuel?

Sorry I took so long to reply, but I been very busy the last few days. Anyway yesterday I took the time to remove all the glow plugs and do the 12V test on them. They all were red hot within 2 seconds and they were all Bosch glow plugs.

As far as the valve clearances, I did them last month, with help of the DIY on DieselGiant.

Now at 65 degrees the engine starts up on the 2nd turn, which to me is normal. Now my odometer reads 337K miles but that can't be right. I changed the oil at the middle of last month, on the sticker I put on the windshield I wrote change the oil at 334K miles, which was a 4K mile period. So if my Odometer is right that meets I drove 7K miles in a month and half.

Looking at the in-line fuel filter, I have one bubble on matter how high I rev the car. The Primer pump has a white top, and it a little bit of fuel in the bottle of the hole.

I'll get back to you on the fuel test.

kerry · #14 04-03-2010, 06:42 PM

Personally, I would do a compression test before doing anything else. It only takes about half an hour and your symptoms are typically of low compression so it's the next logical step.

barry123400 · #15 04-03-2010, 07:05 PM

The choice is yours. The compression test may be more mangable first as there is usually no interpretation required other than reading the numbers. Kerry is right at this time and with the present temperatures.

When checking the fuel supply out you have to pay a lot more atttention to what you are interpreting. The other problem is your real mysery is only present when it is cold.

I was hoping it still started up a little harder than normal when the ambient temperature is warm. It seems to start pretty normal in my opinion. So if there is a problem in the fuel supply it will be impossible or unlikely to be found right now.

At these temperatures it may have to wait even if the compression numbers come back good. Or you will be shot gunning things to find and eliminate the issue.

Your milage may be high enough to have real wear in the engine as well. Yet there was still one component in your post that indicated you may still have reasonable compression.