300D Part I.D. - Problems Starting
 

There are two parts to this post. The first is: What is the part that's in the photograph below? It's located behind the driver's side headlight.

The second this is that my car won't start. Here is what I know so far:

- The battery has plenty of juice (I tested it with a voltmeter and all the accessories turn on with no problem).

- The starter does not engage (doesn't even make a noise) when the key is turned.

- I ran a wire directly from the starter power terminal to the battery terminal. The starter still is completely dead when doing this, however there is a clicking sound coming from the part I photographed below (maybe its a relay)?

- The ground wire from the bell housing to the chassis is clean and has good connection. What other connections could be affecting it?

- No fuses are blown.

I'm thinking the issue is either some sort of relay or that the starter is bad (I just replaced 7 months ago with a remanufactured one).

http://i1219.photobucket.com/albums/...6/300DPart.jpg

Thanks in advance for your help.

Brendan

Glow plug relay, yes? The car won't start without it, or one like it. Why the starter won't engage, maybe a bad new or reman starter, or a bad ground, start with the latter. Could have simply not been grounded securely when replaced and has come loose.

There's a plastic junction box on top of the right fender in front of the battery. Try jumping terminals 1 and 3. If that does not cause your starter to activate, you have a ground problem, a connection problem at the starter or a problem with the starter itself.
It is in Park, correct? A bad NSS can cause those symptoms.

The reason the Glow Plug Relay in the picture is clicking is that when your Key is in the Starting Position and the Starter Solenoid gets Electricity there is a wire that comes up from the Starter Solenoid Terminal and connects to a Violet (Purple?) wire that goes to the Glow Plug Relay.

While the Starter is Cranking the Violet Wire gives your Glow Plug Relay Electricity and your Glow plugs are on while your Engine is cranking.

In other words the relay is fine and is just clicking because the starter isn't cranking?

Update, I had the starter bench tested and its in good working condition. So that only leaves a bad ground or bad connection to the starter right? What grounds are there besides from the bell housing to the chassis?

There are other possibilities if the starter is good but not working in the car. Try jumping the terminals that kerry suggested, if it works the problem may be elsewhere in the starting circuit including the ignition switch or the neutral safety switch on the transmission. Also, try starting it with the car in neutral instead of part and try wiggling the shift lever around.

extremely common issue with these older mb's
it's the shifter bushings on the transmission shifter linkage.
try this. put your emergency break on solid!, then put key in, let the relay click, and wait 25 seconds, then turn the key to the start position and hold it there. now with your left hand, reach under your right hand, and push on the shifter in park, wiggle it to the right while pushing forward. usually this will solve the issues. if it starts fine this way, you need to order all the bushings for the shifter and linkage. it's not hard to change all the bushings, but you will need to get the console out, and get to the shifter parts, and under the car on the linkage to the transmission.

Alright guys, I'm starting to loose hope here... I tried:

- starting it in neutral, and tried wiggling it around too

- starting it how vstech suggested with the ebrake on and wiggling it in park

- jumping terminals 1 and 3 (heard a click from the relay again)

- cleaning off all ground and power wire terminals with simple green and a wire brush.


The only things I can think of is that the battery is low now from trying to start it so much, or that there's a fuse blown that I don't know about. All the fuses are located on the drivers side against the fire wall correct?

A weak battery could indeed be hindering your progress - can you jump start or borrow another battery? Your battery should physically fill the battery tray - sometimes people fit smaller ones 'cos they are cheaper but they aren't always up to the job when they get a bit older.

As I'm paranoid I'd also check to see if I can turn the engine by hand - crankshaft nut 27mm

Good luck.

I don't think any fuses are involved in starting (aside from the relay's fuse which has nothing to do with the starter). It's key->neutral safety switch->starter. Plus if you want to skip all that you can take a small wire and hook the solenoid screw on the starter directly to the battery.

If you want to trace a voltage issue you're going to need a helper to turn the key when trying to start. First, I'd disconnect the GP relay while troubleshooting. That eats up alot of juice and will do more to wear down your battery than anything at this point. You'll need a voltmeter too.

If you are hearing no clicking from the starter relay then you need to find out why. The two connections on the fender are the battery and the starter relay. When the ignition switch is engaged to START, you should see 12V appear at the starter relay terminal. If not, then check your neutral safety switch. If your glow plug relay is energizing, then your NSS should be working. If the starter relay is energizing but not engaging the starter, check the ground from the engine to the chassis. You can test this by engaging the starter and checking the voltage from engine block to the negative battery post. If you see any voltage at all, then you need to tighten/fix your ground connections to the battery and/or engine.

Another way to test the engine ground is tho connect a jumper cable from the engine to the negative battery terminal and see if it works then.

Thanks guys. I will try all those suggestions.

"Army" - The battery is brand new (has about 5k miles on it) and it does take up the entire tray. I'll try cranking the engine manually like you suggested... I hope that's not the problem!

"aaa" - I've already connected a wire directly from the starter solenoid screw directly to the battery and still nothing other than the relay clicking.

I'm assuming since directly connecting the wire didn't work that it must be a ground issue. Running the wire from the solenoid screw to the battery should bypass all the other potential issues regarding the NSS, shifter bushings, etc. Right?

If you pulled out the starter and it worked fine on the bench, then yes, it appears something is wrong with the electrical connections to the starter when it is installed. So I would try if possible to bypass the standard electrical connections in the car and jump it while in the car. Ground the engine or starter to the negative post on the battery as Craig suggested and try it. If that doesn't work, also jump the positive post on the battery directly to the starter if possible and see if that works.

On a related note, when I have jumped terminals 1 and 3 in the junction box, I don't remember the glow plug relay clicking. Does anyone else?

At this point I'd lean towards a toasted starter. Usually the solenoid is stuck, I've whacked the starter with a hammer in a pinch to get it working temporarily. Go ahead do the ground thing.

If it's bench testing ok, why would the solenoid stick when it's in the car?

Ah I missed that part.

Jumping Terminal 1 to Terminal 3 makes a direct connection from Circuit 30 (Unswitched 12VDC) to Circuit 50 (Cranking). This should energize the glow plug relay through the ignition switch wiring.

Offering hope/support. :)

Don't freak out if the engine does not want to crank with a ratchet, consider the following.

I had two last year.

#1. Turned out to be a broken flywheel that dug into the bell-housing jamming the starter.
A local shop had quoted $7,000.00 repair.

#2. Was a locked A/C compressor and alternator, very strange they both failed at the same time.
A local shop quoted $2,500.00 to install a good used engine.


Both owners had given up, and I convinced them to let me diagnose the problem = fix it under $500.00 or part it out and split 50/50 with the owner..

Owner #1 stuffed money in my pocket when I showed him the problem, and DIY replaced the flywheel with a spare. :D

Owner #2 had me cut the A/C belt and replace the alternator + stuffed enough money in my wifes purse to make her grin for two weeks. ;)

Offering hope/support. :)

I tried jumping the car (thinking the battery might have been drained from trying to start it so many times) and still nothing! Arg!

Ok, so connections to the starter... there is one small power wire that connects to the starter solenoid with a small screw. There are two ground wires that loop over a bolt on the starter and are fastened down with a nut. Is this correct? Where do these these two ground wires run to? Maybe one of them is faulty and that's why the starter wont engage.

I'm starting to think maybe I connected the wires incorrectly to the starter. Can someone tell me how the connections should be set up?

Those aren't ground wires, they're power wires. One of them goes direct to battery (always live...). Ground is via the engine body, there's a braided harness on the other side of the engine to the chassis.

Ok, so one goes to the battery and one goes to the terminal in front of the battery (that connects to the glow plug relay)? What about the wire from the starter solenoid? What should that connect to?

Anyone? OR can anyone point me to a diagram that may help? I've tried searching but cannot fond the answer.

Answer
 

Both large cables go on the top starter solenoid stud.
The small wire is attached with a screw.

To test cranking directly on the starter.
Jump from the small wire to the top starter solenoid stud.


If you are asking what controls the circuit.

Ignition Cylinder Tumbler replacement + Key issues; mixed diesel/gas
http://www.peachparts.com/shopforum/diesel-discussion/142232-ignition-cylinder-tumbler-replacement%3B-mixed-diesel-gas.html#post1065596

Broken Neutral Safety Switch and replacing shifter bushings
http://www.peachparts.com/shopforum/diesel-discussion/96048-broken-neutral-safety-switch-replacing-shifter-bushings.html#post646647

Replacing all shifter bushings on W126 - p.1
http://www.peachparts.com/shopforum/diesel-discussion/112582-replacing-all-shifter-bushings-w126-p-1-a.html

I tried jumping directly from the small wire to the stud as whunter said and still nothing. This must mean a bad ground correct (since the starter was bench tested and worked fine)?

Answer
 

Correct.

The factory ground goes (under the car) from the (17 MM bolt) transmission bell housing to the (13 MM bolt) body = if it is loose or damaged = no cranking.

As a fast diagnostic TEST, take jumper cables:

#1. Attach both clamps at one end to the engine METAL.

#2. Attach both end clamps to the Negative battery terminal, you may need someone to hold them in contact.

#3. Try jumping the starter again..

If it cranks..

Here is a cheap fix + extra insurance that I use due to Michigan corrosion:

Get an aftermarket ground cable, long enough to go from:

Point "A". The battery ground cable 13 MM body bolt.

Point "B". The "T" shaped air cleaner mounting bracket, top rear 13 MM bolt = remove the air cleaner housing.
Note: On naturally aspirated engines you will need to choose an alternative engine attachment location.

At worst it does nothing but double your ground = reduce resistance.
Generally it improves cranking ability.
In your case, it should get you running again..

Thanks whunter.I've now tried about everything. I tried grounding with jumper cables (they are a nice thick gauge too) with no results. So I went about it methodically. I:

- ran a cable directly from the positive battery terminal to the solenoid stud. Then I jumped the stud and screw. Nothing happened so the problem isn't power, must be ground (or starter itself).

- Then I clamped a jumper end to the ground stud on the starter and the other end to the chassis, still nothing.

- Then I added an additional ground strap as you suggested. I ran it from the 13mm bolt used to ground the battery to the air filter T-bracket. Still nothing.

What the hell is going on?! I've tested every logical possibility! I'm about to take out the starter and have it bench tested again. Maybe something has happened to it since it was tested 3 weeks ago. Either that or despite all my grounding attempts I'm STILL not getting enough ground.

:/

OK
 

The basic circuit is in picture #1.

If it does not function it could be a mechanical issue:

#1. Manually crank the engine roughly 45° listening for a snap/clunk, (Example: Degree wheel), this should release the starter gear from the flywheel if it has jammed = possible bad starter gear.

#2. Apply power to the small screw and use a hammer to whack the side of the solenoid/rear of starter = possible bad starter.

Shortened my post intentionally. A couple of things perhaps not checked as far as I read into your posts. The integrety of the battery post to battery cable connection is a common failure . Did you clean both the terminals and battery cable clamps? Or with a friend put one lead from a voltmeter on the actual battery post terminal itself and the other lead on the clamp. Then moving the key into the starter position. There should be little voltage displayed in your case actually nothing. Do both terminals in this fashion.

The second thing was your description of using the battery jumper cable to the engine. I like to use a really good ground area like a clean alternator bracket or something simular. Anyways without verifying the battery post to battery cable clamp has little resistance first the use of the jumper cables from the clamp area can be meaningless. Now you very well may have taken care of these areas of concern already. But if not you should.

When I started my first post I quickly realised I was writing far too much information about the starter circuit down. I can add more later if the indication is I should. A friend that has more experience around cars than you can be an asset in itself remember. Starter circuits are very simular car brand to car brand usually so he or she need not have mercedes experience.

I took the starter back in to get tested and be 100% it wasn't the starter itself. Starter tested fine again.

I bought 2 extra ground straps and installed them. Now the starter is making a clicking sound and trying to turn over! So that's improvement at least. Seems like I still need to add some more ground points to reduce resistance to the starter. Either that or the battery needs to be charged from trying to start the car so many times.

It is tricky solving a problem like yours - you really need to get your ducks lined up so that it works - you could be fixing one link in the chain and then not realising that another link is now bust (if you see what I mean)...

...All I can do is to encourage you to be as methodical as possible with each stage.

EDIT:- Have you cranked the engine by hand yet?

No, I haven't cranked it by hand yet. Before, the starter wasn't even clicking so I figure cranking it wouldn't do any good as the starter gear wasn't trying to engage.

Be brave and put my mind at rest! Give it a quick churn - 27mm socket on the crankshaft bolt - it is all the way inside the pulley... Whilst you are at it do just like whunter recommends in the post above => http://www.peachparts.com/shopforum/2649685-post30.html

Well, I added 2 ground straps directly from the starter to the frame and viola! Starts like a champ now. Thanks to everyone for their input and suggestions.

Moral of the story is that ground issues are very tricky to solve! It's amazing that these cars only have one chassis to frame ground strap.

Thanks again everyone.