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  #1  
Old 02-01-2009, 07:00 PM
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very confusing STARTER / IGNITION issue

have a very strange start / no start issue, even though i've got a good new battery.

my '85 300td hasn't been run for awhile, due to a looong head job, but now she's back in action except for a strange starter / ignition issue:


when turning the key, she


SOMETIMES will just click from the solenoid, with no start. It can happen 10 times in a row, and then maybe she'll start fine.

SOMETIMES will start fine but the starter continues running even after the key is released. I can only make her stop by disconnecting the battery, and the starter motor will usually start right back running if i reconnect the cable...even with the gearshift in another position/gear. This is the situation I'm currently in...If i connect the battery ground, the starter engages, even with the ignition "off".

SOMETIMES
I can turn the key and get a click, and get her to start by slowly moving the gearshift in/out of the Neutral position. But I hear her click on/off multiple times as I move the shifter, and it kind of seems like rather than a NSS problem, she's starting simply because by moving the gearshift back and forth I'm sending multiple signals to the starter...as if i was just turning the key off/on lots of times.

I've cleaned the little terminals on the firewall, and no change.
I've removed the starter and had it tested at NAPA...it passed and worked fine on the bench.
It kindof seems like the key switch doesn't move or release as freely as my other Mercedes....

thoughts?
tests?
diagnosis?
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'85 mercedes euro 300TD

proud owner (in days gone by) of:
'77 mercedes 280e
'80 mercedes euro 250
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'82 mercedes euro 250
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  #2  
Old 02-01-2009, 08:41 PM
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It may be the Ignition Switch.
If the Key is in the off position you should be getting no Voltage at the wire that goes to your starter solenoid.
I suppose another possible would be if those wires that go to the Terminal Block in front of the Battery and on the Pasanger Side Fender well are some how making contact.
See where the 2 wires run together inside of the same rubber loom (however this is on an 84 300D) if the wires are rubbed through the instalation and they make contact (+) voltage will go to the other wire.

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Last edited by Diesel911; 02-01-2009 at 08:47 PM.
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  #3  
Old 02-01-2009, 08:52 PM
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Sounds like you have 2 issues here.

1. Neutral Safety Switch
2. old dirty oily starter

My W123 300D did this when I got it, the starter would continue cranking until it killed the battery. The starter had 23 years of gunk and oil and dirt inside it, causing the armature to stick, either not engaging or engaging and sticking. Cold weather made it worse.

I replaced it and the sticking issues stopped.
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  #4  
Old 02-02-2009, 11:29 AM
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in addition to what was mentioned:

The clicking sounds like typical starter failure. Next time you get a click and no start, grab a heavy wrench and beat on the starter mildly. -about half the force it takes to drive a nail into hard wood.
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  #5  
Old 02-02-2009, 11:35 AM
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I'd agree that is is a starter issue.

If it were the neutral safety switch, you wouldn't get any click before you moved it.
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  #6  
Old 02-02-2009, 11:45 AM
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Yep, I agree...my old ignition switch had to be removed and cleaned from gunk inside making electrical connections...Ive also seen where it was a mixture of two problems ESPECIALLY after a service! Gunk inside the old merc switches is not an uncommon problem...theres DIY forums on here that deal with that very problem!
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  #7  
Old 02-02-2009, 11:52 AM
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Quote:
Originally Posted by Putty View Post
Yep, I agree...my old ignition switch had to be removed and cleaned from gunk inside making electrical connections...Ive also seen where it was a mixture of two problems ESPECIALLY after a service! Gunk inside the old merc switches is not an uncommon problem...theres DIY forums on here that deal with that very problem!

will the glowplugs still glow if is the switch?
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  #8  
Old 02-02-2009, 04:00 PM
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firewall

so, the starter is currently spinning anytime i connect the battery ground...even with the key "off".

if i connect the battery ground and then put my test light to the 3 terminals on the firewall that are shown in Diesel911's post above, i get current at all three terminals, even with the key "off."

does that mean it's definitely the ignition switch? (in the dash)?
or is it still up for debate?
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'85 mercedes euro 300TD

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'77 mercedes 280e
'80 mercedes euro 250
'80 mercedes 300TD
'82 mercedes euro 250
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  #9  
Old 02-02-2009, 04:40 PM
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Quote:
Originally Posted by blankenship View Post
so, the starter is currently spinning anytime i connect the battery ground...even with the key "off".

if i connect the battery ground and then put my test light to the 3 terminals on the firewall that are shown in Diesel911's post above, i get current at all three terminals, even with the key "off."

does that mean it's definitely the ignition switch? (in the dash)?
or is it still up for debate?
Again refering to the pic below and Key in the Off position; with my test light cliped to the negative terminal of the batter and putting the pointed probe on the far left terminals I get a light (+ voltage; also not the 2 conectors on the are hooked to the same strip of metal and are both (+).

When I do the same to the far right terminal with the White and Purple wire conneted to it I get no light indicating no current going through that wire with the Key in the off position.

Added: I dosconnected the Purple and White wires on the far right.
I hooked up my Meter to the Purple wire. With Key off there was no voltage. I had to turn the Key all the way to the Start position to get voltage.
The above test showed no voltage to the White wire (remember it is disconnected from the Terminal Block) at all.


I used a Jumper Wire from the (+) terminal of the Battery to the White wire and the Solenoid activated and my Starter started to crank.


The White wire (to the far right in the picture) is the one that goes to the Starter Solenoid and the Purple wire is that one that feeds the White wire the (+) voltage when the Key is all the way in the start position.


If the Key is in the Off position and you are still getting voltage to that Purple wire you have a problem from that wire back. (When I looked at the wiring diagram I was not clear to me where exactly the wire goes.)

If you disconnect the White wire on the far right and your Starter is still cranking you have a short circuit feeding (+) voltage to Starter or the Starter Solenoid is stuck.

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Last edited by Diesel911; 02-02-2009 at 06:28 PM.
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  #10  
Old 02-02-2009, 07:10 PM
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I think a have figured a way you can tell if it is the Ignition Switch or not.

The (+) voltage goes through the Ignition Switch when the Key is in the start position and goes to the Starter lock out/Back up light switch on the side of the transmission. From there by way of a VI wire (Purple) it eventually splits with one Purple wire going to that Terminal block (to activate the Starter Solenoid and Crank the starter) while another Purple wire before it reaches that Terminal block has split of and goes to the Glow Plug Relay (this is the wire that keeps the Glow Plugs on while the Starter is cranking).

There should be a Purple wire in the small square Connector on the picture Glow Plug Relay


Here is where the fun starts.
Disconnect the small square Connector on the Glow Plug Relay (this is to bypass and make sure that a bad Glow Plug relay is somehow supplying (+) voltage to the Purple wire).

Next; with the Ignition Key in the Off position Connect your test light to the far right side of the Terminal Block where the Purple wire screws in. If your test light lights and your Ignition Key is in the off position your Ignition switch is the problem. (It cannot be the Starter lock out/Back up light switch because that switch gets the power from the Ignition Switch.)

If you do the above test (remember the Ignition Key is still in the off position) and your Test Light does not light up; plug in the Small Square Glow Plug Relay Connector. If you your Test Light lights up when the Connector is plug in it means you have a short circuit in your Glow Plug Relay and it is giving (+) voltage to the Purple wire when it is not supposed to.

I think the above is easier to do than it is to write instructions for.
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Last edited by Diesel911; 02-02-2009 at 07:28 PM.
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  #11  
Old 02-03-2009, 06:14 PM
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purple

well, per Diesel911's suggestion, I removed the "far right" wires (purple and white) from the terminal block, and tested each for current with the key off.
i DO get current on the white wire.
i DO NOT get current on the purple wire.

I guess this obviates the glow plug test mentioned in the last post...if I'm not getting power on the purple wire with the ignition off (and yet my starter is still turning), it's not the ignition switch's fault. right?

So, figuring it must be a bad solenoid, I reached down to explore that tight cavity so I could find a good spot to tap on it with a wrench. I pushed the solenoid wires around quite a bit, and then reconnected the battery without doing any 'tapping'. Suddenly everything suddenly seems fine! Starts/stops as it should.

Hard for me to imagine it's the wires, though...they have rubber insulation and a woven white insulation, and I can't get the starter to come on now by any amount of 'jiggling.' Also, how would bad wires explain the occassional "click / no start" condition?

Should I assume bad solenoid anyway, and chalk my recent luck up to 'luck'?
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'85 mercedes euro 300TD

proud owner (in days gone by) of:
'77 mercedes 280e
'80 mercedes euro 250
'80 mercedes 300TD
'82 mercedes euro 250
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  #12  
Old 02-03-2009, 07:23 PM
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If it was the tapping, that is your starter going bad. The brushes are worn and tapping them knocks them into place / disrupts the non-conductive garbage that has accumulated in them.

If its the wires (praying) you should be able to re solder. (unlikely)

You might have a few good weeks of rapping on your starter each morning before it leaves you stranded somewhere. - take note if it happens more on damp or cold mornings versus mild or dry.
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  #13  
Old 02-03-2009, 09:42 PM
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Quote:
Originally Posted by blankenship View Post
well, per Diesel911's suggestion, I removed the "far right" wires (purple and white) from the terminal block, and tested each for current with the key off.
i DO get current on the white wire.
i DO NOT get current on the purple wire.

I guess this obviates the glow plug test mentioned in the last post...if I'm not getting power on the purple wire with the ignition off (and yet my starter is still turning), it's not the ignition switch's fault. right?

So, figuring it must be a bad solenoid, I reached down to explore that tight cavity so I could find a good spot to tap on it with a wrench. I pushed the solenoid wires around quite a bit, and then reconnected the battery without doing any 'tapping'. Suddenly everything suddenly seems fine! Starts/stops as it should.

Hard for me to imagine it's the wires, though...they have rubber insulation and a woven white insulation, and I can't get the starter to come on now by any amount of 'jiggling.' Also, how would bad wires explain the occassional "click / no start" condition?

Should I assume bad solenoid anyway, and chalk my recent luck up to 'luck'?
Yes, no current to the Purple wire indcates that your Ignition Switch is working= in the off position = no current to the Purple wire.
Sounds like you have a short circuit in the wires somewhere. A (+) wire is making contact with something on your starter that will cause it to crank.

Go back to the pic of the terminal block and you will see that the 2 white wires go into the same plastic tube.
The White Wire on the Left of the Pic is a (+) wire and the Wire on the Right of the Pic (this wire goes down to the Solenoid). So if that (+) wire has rubbed through the insulations and makes contact with Wire that goes to the Solenoid (somewhere inside of that plastic tube) your starter will crank.
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  #14  
Old 11-05-2009, 02:59 PM
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done & done

replaced the starter back on 2/4...solved the problem.

ahhhhhhhhhhhhhh...closure.
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'85 mercedes euro 300TD

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'77 mercedes 280e
'80 mercedes euro 250
'80 mercedes 300TD
'82 mercedes euro 250
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