300SD electrical starting problem

[James L]

have replaced glow plugs, belts, voltage regulator and battery all within this past year. however, lately and at various times i have had to jump start. have tested battery and it has 12 volts with no eratic surges when key is on or when at high idle.

thanks for help
James L
1983 300SD 188K

[jeffsr]

Try starting the engine and then disconnecting the negative cable from the battery. If it quits, the the alternator is not charging. I'd start there.

------------------
Jeff L
1987 300e
1989 300e
1987 BMW 325

I guess I'm missing something. This is a diesel engine. It should remain running after started, even with no battery in place.

Does this model have some sort of electrical shutoff or something?

Just curious,

------------------
Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

PS. I have had solenoid trouble in the past that would have fit your set of circumstances. The solenoid is replaceable, but I wouldn't bother unless you have a very good starter. I replaced the solenoid on a jakeleg rebuilt starter to no avail. I've replaced the solenoid a few times on Bosch certified rebuilts and it worked both times.

Good luck, LB

[This message has been edited by LarryBible (edited 05-02-2000).]

Yes I have heard of a bad spot. I've had some cheap starters that would not do anything, even with a hot battery. I didn't hit the starter with a hammer, although that may have worked, I took the plain end of my pretty nickel plated lug wrench and shorted momentarily between the hot cable at the solenoid and the large cable going to the starter motor itself. CAUTION, when I did this, it was after checking about five times to ensure that the transmission was in neutral. After giving it a quick spin like this, I was almost always able to start it with the key normally.

I'm not sure if this situation is a bad spot on the commutator, or a flaky solenoid.

After rereading the original post, you said that there was 12 volts at the battery at idle. If this is the case, the alternator is not putting out. You should measure about 12 volts with the engine stopped, and about 13.5 to 15 volts with the engine running. If you have 12 volts with engine running, you either have a bad alternator, or a problem with the associated wiring. I had to resolder the heavy wire in the alternator cable a few years ago. It will show up as a bad alternator unless your testing thoroughly with your multimeter.

Also, don't rely on the alternator light on the instrument panel. Benzmac said that the light circuit passes through the brushes. Since my alternator (battery symbol) light on the instrument cluster has rarely been of any use when I've gone through these problems, what he says makes good sense (as does most of what he says).

Sounds like you need to check the battery voltage again. If it's 12 volts with engine running, check your alternator wiring, if it's okay, replace the alternator or the brush pack.

Good luck,

------------------
Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

[jeffsr]

OOPs!! forgot it was a diesel. Disconnect battery and check charging voltage at the battery cables. Should be more than 12 volts at idle.

------------------
Jeff L
1987 300e
1989 300e
1987 BMW 325

[James L]

just retested with multimeter; while running at high idle and testing at battery terminals, reads 12.88 - 13.0 volts (actually drops a few decimals when i excellerate the throttle link). when i turn off the enginer it reads 12.88. all the conections and wires seem ok.

also when adjusting the valves on the 5 cylinder diesel, do you really need those 3 thin $65.00 bent wrenches? can you not use a crows foot wrench and universal extension?

thanks
James L
1983 300SD 188K

James,

Sounds like the alternator. Check the connector at the alternator, ensure continuity back to the large starter cable.

I have managed to adjust valves in the past before I bought the wrench set, but you need to make sure you have enough bad words lined up before you start, it's challenging without the wrench set.

Good luck,

------------------
Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

[stevebfl]

I would like to issue a word of warning. I would advise against removing the battery cable while running. This may be appropriate for testing generators but it won't work to test most alternators, plus modern electronics do not like the spike voltages that occur when loads are dropped instantly.

------------------
Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

Beyond the fact that it's not healthy for the cars electronics, if you have a voltmeter, you should never have to do this for troubleshooting purposes.

Here's another "old codger" story. When alternators came out in the mid sixties, many of them bit the dust because of people striking the jumper cables together after connecting them to the good battery. They did this in the generator days to see if they had a good connection and a hot battery. (Also it was probably quite fun to make sparks) Then they would connect to the vehicle needing the jump. The diodes didn't like this technique very much.

Larry

[James L]

ok now the hood release handle and possibly the cable has broke so i can not open the hood. therefore i could not jump start it this morning when it did not turn over. i just sat there turnning the key with no nose or nothing then finally and suddenly it turned over and cranked causing me to be late again for work (this car may get me fired!i have a daily 40 mile commute) my other car is a much more undependable, worn out (240K) 1987 BMW 325i with a whole bunch of problems.
i think the problem with the 300 SD could be a relay or a switch of some sort?

thanks
James L
1983 300 SD 188k
1987 325I BMW 240K, electrical problems galore!, sun roof, door and trunk leaks, oxidized and peeling cirrus blue paint, ect..., ect..., ect...

James,

My experience says that you need a starter. I could be wrong, but that's been my experience. The starter on any diesel lives a very tough life. I've experienced the symptoms you've dealt with and for me it has always been the starter. If you have a good starter MOTOR, you may very well get by with replacing only the solenoid. If you have the tools and facilities to change the starter easily, you might want to risk $30 or $40 for a solenoid. If you want to fix it and be done with it, a rebuilt starter would be your best bet. Also my experience has been that spending money for a starter at your garden variety parts store is false economy. Find the best price on a Bosch authorized rebuilt. The parts shop on this website may be your best bet.

Good luck,

------------------
Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

[James L]

Larry i think your right about the solenoid, maybe the electrical connection has oil crude causing a short, could i be so lucky? how do i get the hood open? i have pulled hard with pliers and the hood still will not open!

thanks
James L

[James L]

Bill, that's exactly what happened; plastic piece fell to pieces but handle is still attached to wire. i will try vise grips.

thanks
James L

[DieselGuy]

The same thing happened to me 2 months ago on my '84 300sd...the hood release handle broke off. I tried using vise grips of all sorts and sizes but didn't want to damage the cable by yanking it in a manner it wasn't meant to be. I was happy to find that the MB dealer had a replace ment handle and bracket mount...they come together for the low price of $6.

James,

Once you get your new plastic handle and get the hood open. You can of course ensure that the battery cables are in good shape and tight. Also check the primary wire to the starter to ensure that it has a good crimp from the wire to the connector. You, of course, should always check connectors and wiring before purchasing parts.

However, the symptoms you describe indicate, in my experience, that you're solenoid and/or starter are the culprits.

Because the primary wire to the starter is relatively light and the current comes through the ignition switch, they are stressed, as the solenoid gets old and tired causing the solenoid current to increase. Many years ago, I took the primary starter wire and connected it to the primary side of a heavy starter relay, the kind found on most all Fords. I then connected a heavy cable from one of the secondary terminals on the relay to the positive battery terminal. I then connected another heavy cable from the other secondary relay connection to the primary side of the starter. This provides a heavier connection from the positive side of the battery to the solenoid. It saves the ignition switch and provides a more substantial connection to the solenoid. It's worked well for me for many years.

Good luck,

------------------
Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles