300sd challenge
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Mercedes Benz 300sd Turbo Diesel
300sd challenge
It's not turning over at all, but all the electrical comes on. From what I read the problem is mostly likely electrical in nature. My battery is new, within the last six months. It holds it's power just fine, there's no drain except for a tiny bit from the radio. The alternator is new. The power cable to the battery is new too, and the ground has been cleaned. The starter is new. There was no sharp clunk the last time in ran. The ignition switch is also new. And of course the shifter is in park. Power is being sent to and from the neutral safety switch. I've wiggled the shifter while turning the key and nothing happened. The back up lights work. The tumbler doesn't seem sticky, the key comes out just fine. The glow plug light comes on, all the glow plugs have been replaced in the past year. All the wires to the starter test 0 resistance. No fuses are blown.
Any ideas? I'm pretty experienced, and I've had two other mechanics look over the car and they're stumped too.
Thanks!
Any ideas? I'm pretty experienced, and I've had two other mechanics look over the car and they're stumped too.
Thanks!
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Joined: May 2013
Posts: 10
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From: PNW
1989 420 SEL
So you are saying you turn the key to start and the electric starter motor does not go?
First measure the battery voltage with the car off. A fully charged car battery is 12.75 volts. If it is not fully charged (like 12.0 volts or 11.5 volts) charge it with a battery charger.
Then check to see if you have power to the starter with a voltmeter. That is to the big + cable and to engine ground.
Then see if you are getting power to the little wire at the starter when you turn the key.
Is the starter clicking when the key is turned?
FYI just because something is new does not mean it is working. So troubleshoot everything like normal - don't assume something is not the problem because it is new.
First measure the battery voltage with the car off. A fully charged car battery is 12.75 volts. If it is not fully charged (like 12.0 volts or 11.5 volts) charge it with a battery charger.
Then check to see if you have power to the starter with a voltmeter. That is to the big + cable and to engine ground.
Then see if you are getting power to the little wire at the starter when you turn the key.
Is the starter clicking when the key is turned?
FYI just because something is new does not mean it is working. So troubleshoot everything like normal - don't assume something is not the problem because it is new.
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Mercedes Benz 300sd Turbo Diesel
Here's the readings I have: The battery is charged to 12.83. When I turn the key the ignition wire to the solenoid is 11.21, the battery to the starter is 11.66, and when the key is turning the battery drops down to 11.64. The starter isn't clicking, the only noise is from the glow plug relay.
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Joined: May 2013
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From: PNW
1989 420 SEL
And the above was using the engine ground for negative (-)? (The wire to engine ground can be bad, loose, dirty.)
Anyway if that test included testing using the engine ground, then sounds like you have a bad starter / starter solenoid.
Anyway if that test included testing using the engine ground, then sounds like you have a bad starter / starter solenoid.
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Mercedes Benz 300sd Turbo Diesel
I took the starter out to have it re-tested- and it passed at autozone. I had the battery tested and it didn't, so I got a bigger new battery as a replacement yesterday. I put everything back together and tried it only once- and it tried but then failed, and now it's back to only the lights, dash, and radio turning on. I tested the resistance for the ground for the battery and it was 0, and then the starter's ground, which was 0. I found resistance in the wire that goes from the junction to the solenoid 5.6 ohms. But when I used a jumper wire from the battery to the solenoid the glowplug relay just clicks.
I talked to someone at autozone and he said sometimes when the gear from solenoid doesn't line up with the flywheel it'll pull back and won't start- I'm not sure what he was talking about... anyone know?
Thanks for all the replies!
I talked to someone at autozone and he said sometimes when the gear from solenoid doesn't line up with the flywheel it'll pull back and won't start- I'm not sure what he was talking about... anyone know?
Thanks for all the replies!
Last edited by beccajopechin; Jun 4, 2013 at 04:05 PM.
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From: PNW
1989 420 SEL
The starter solenoid (small round part of the starter) has a round push rod which moves in/out electrically. This does two things. It makes the gear on the starter move forward so it engages the engine flywheel and also connects a electrical contact to make the electric starter motor start turning.
Click on the 4th picture at the following and you will get a bigger picture - the picture showing the various parts. Part 6 is the solenoid and you can see it has a lever attached to it and as it slides left/right, it makes the gear below move right/left.
https://en.wikipedia.org/wiki/Starter_(engine)
Here is an animation...
If that gear can't slide fully into the engine flywheel gear for some reason, then it also will not activate the electric switch to turn on the starter motor. That could happen if there was gunk, part of a broken off gear, or some other obstruction on the engine flywheel gear tines - keeping it from sliding forward...
...Or if that is not the correct starter and the gear on the starter can't "mesh" with the flywheel gear because it is different. Is that the correct starter?
A mirror and a flashlight might be helpful to examine the engine flywheel with the starter removed - see if there is some obstruction in there.
Also possible that is the correct starter part number, but someone installed the wrong gear on it and it will not mesh with flywheel?
Or maybe the wrong starter in the right box or mislabeled?
Click on the 4th picture at the following and you will get a bigger picture - the picture showing the various parts. Part 6 is the solenoid and you can see it has a lever attached to it and as it slides left/right, it makes the gear below move right/left.
https://en.wikipedia.org/wiki/Starter_(engine)
Here is an animation...
If that gear can't slide fully into the engine flywheel gear for some reason, then it also will not activate the electric switch to turn on the starter motor. That could happen if there was gunk, part of a broken off gear, or some other obstruction on the engine flywheel gear tines - keeping it from sliding forward...
...Or if that is not the correct starter and the gear on the starter can't "mesh" with the flywheel gear because it is different. Is that the correct starter?
A mirror and a flashlight might be helpful to examine the engine flywheel with the starter removed - see if there is some obstruction in there.
Also possible that is the correct starter part number, but someone installed the wrong gear on it and it will not mesh with flywheel?
Or maybe the wrong starter in the right box or mislabeled?
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From: PNW
1989 420 SEL
Another possibility...
Here is a close-up picture of that starter gear...
http://www.lulusoso.com/upload/20120...pg_250x250.jpg
Notice the ends are sort of knife shaped. That is if the starter gear does not exactly line up with the flywheel, the solenoid (with enough electrical power) will "force" that gear into the flywheel and it will turn a bit as doing so. That takes a LOT of electricity.
You have cleaned/checked/replaced everything under the sun... But maybe there is a poor electrical connection from ground to the starter or on the positive side from the battery to the small starter solenoid connection or park/neutral safety switch. Or maybe that battery is not the correct battery for your car and does not have enough power????
To test that theory, try jump starting the car. You would be getting extra electricity from another car's battery.
Then only do the following if you totally understand what you are doing (which it sounds like you do). But this can be very dangerous or you could damage the electrical system if not done right.
That is with the car in park, parking brake on, and BIG wheel chocks, rocks, wood, whatever blocking the car's wheels so the car absolutely can't move (safety)...
...to use a jumper cable or large gauge wire from the car battery positive to the starter solenoid positive connection. See if it starts by doing that. The danger in doing this is if you forget to leave it in park, the car can move when doing this. So make DARN sure the car can't move and it is in park.
Better might be to connect a large gauge wire to the starter solenoid (disconnect other wire for testing), then touch that to the battery positive terminal. (You would not be under the car.)
If that works, here are electrical diagrams for 86 and on. That would show what all is along the path of the solenoid starting power (key switch, etc.)...
http://www.startekinfo.com/StarTek/o.../126from86.pdf
Here is a close-up picture of that starter gear...
http://www.lulusoso.com/upload/20120...pg_250x250.jpg
Notice the ends are sort of knife shaped. That is if the starter gear does not exactly line up with the flywheel, the solenoid (with enough electrical power) will "force" that gear into the flywheel and it will turn a bit as doing so. That takes a LOT of electricity.
You have cleaned/checked/replaced everything under the sun... But maybe there is a poor electrical connection from ground to the starter or on the positive side from the battery to the small starter solenoid connection or park/neutral safety switch. Or maybe that battery is not the correct battery for your car and does not have enough power????
To test that theory, try jump starting the car. You would be getting extra electricity from another car's battery.
Then only do the following if you totally understand what you are doing (which it sounds like you do). But this can be very dangerous or you could damage the electrical system if not done right.
That is with the car in park, parking brake on, and BIG wheel chocks, rocks, wood, whatever blocking the car's wheels so the car absolutely can't move (safety)...
...to use a jumper cable or large gauge wire from the car battery positive to the starter solenoid positive connection. See if it starts by doing that. The danger in doing this is if you forget to leave it in park, the car can move when doing this. So make DARN sure the car can't move and it is in park.
Better might be to connect a large gauge wire to the starter solenoid (disconnect other wire for testing), then touch that to the battery positive terminal. (You would not be under the car.)
If that works, here are electrical diagrams for 86 and on. That would show what all is along the path of the solenoid starting power (key switch, etc.)...
http://www.startekinfo.com/StarTek/o.../126from86.pdf
Last edited by Elektrische; Jun 5, 2013 at 07:46 AM.
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Newbie
Joined: May 2013
Posts: 10
Likes: 0
From: PNW
1989 420 SEL
Pretty much auto parts just have part numbers on them and no measurements or specifications. So about all you could do would be to place it side by side with another known correct starter and see if you notice any differences.
But I wouldn't imagine there would be any of those sitting around at any auto parts stores. I usually have to order everything.
If you bought that starter from an auto parts store, maybe you could go back there and get the phone number of the manufacturer or rebuilder. And maybe you could call them and they could have you measure the gear or look for numbers on the starter over the phone?
Wrecking yards sometimes have parts sitting on their shelves. Maybe they would be nice and let you compare your starter with theirs?
Or maybe a local Mercedes mechanic has an old or new one sitting around?
But I wouldn't imagine there would be any of those sitting around at any auto parts stores. I usually have to order everything.
If you bought that starter from an auto parts store, maybe you could go back there and get the phone number of the manufacturer or rebuilder. And maybe you could call them and they could have you measure the gear or look for numbers on the starter over the phone?
Wrecking yards sometimes have parts sitting on their shelves. Maybe they would be nice and let you compare your starter with theirs?
Or maybe a local Mercedes mechanic has an old or new one sitting around?
