Wont start, don't know where to look next. 1992 300D - Page 2 - PeachParts Mercedes-Benz Forum

whunter · #16 01-07-2014, 03:15 AM

Quote:

Originally Posted by thebenstenator

Well, I honestly can't tell you what's going on. I turned the engine by hand, there's expected resistance and the torque converter turns also. (At the time of writing the first post I had all the glowplugs out for replacement. I also charged the battery for good measure.)
After turning the engine a bit by hand I decided to give it another go with the key. Same results. I could hear the starter turning, and the tach read about 1000 rpm and it wasn't turning the engine.
Then I decide to film it so you guys can see what's going on. I set up my camera, go turn the key again and what do you know, the engine turns over!
I'm still confused as heck, but decide to put the glowplugs back in and try it out again.
After that I try the engine again aaaaaaaannnnndd back to square one. So I decide to set up the camera AGAIN and catch it on camera and wadda ya know! The car starts!

Good news? Bad news? I dunno.

Well I jack the car down and one last time decide to try to get video of it. Just in case. And I caught it! It's from my phone camera, so it sounds pretty crappy, but you'll see on my first attempt the starter spins, tach at 1000 rpm, and on the second attempt it actually starts right up.

Starter - YouTube

You can tell from the sound = it is a Bendix issue = failure to engage.

Replace the starter again.

.

vstech · #17 01-07-2014, 05:01 AM

Quote:

Originally Posted by thebenstenator

That's interesting, because I just replaced the starter. . . last week. . . With a new one

I'm guessing you did not get a NEW Bosch starter...

sixto · #18 01-07-2014, 03:40 PM

Or the ring gear is really messed up. See if you can take pictures of the ring gear when you remove the starter.

Sixto
87 300D

funola · #19 01-07-2014, 04:30 PM

Quote:

Originally Posted by sixto

Or the ring gear is really messed up. See if you can take pictures of the ring gear when you remove the starter.

Sixto
87 300D

That, or another possibility is loose electrical connections at the starter, which can result in less "ommph" in the starter solenoid pulling in (to engage the overrunning clutch and supply power to the motor). I don't think it is a bad starter(since you just replaced it). I would do more tests and try other things before replacing the starter again, which is not an easy job.

While cranking the starter, I have never seen the tach register a reading on the W123. Your's is an anomaly. Isn't there a load reduction relay while cranking and isn't the tach one of the items on it (purpose is to cut out unnecessary loads while starting, like the radios, blower etc.

I don't think the 1000 rpm reading is related to an unengaged but spinning starter. They are separate issues. The tach pickup is on the harmonic balancer. How do you explain an unengaged starter making the tach read 1000 rpm? Wouldn't the crankshaft have to spin at 1000 rpm for that to happen?

I'd suggest:

1. Check and tighten starter motor elec connections. Don't overtighten! It's studs are on plastic!

2. Take out the tach amp and clean the contacts.

If 1 & 2 does not cure the problems. Take out cluster and clean the circular connector contacts and check and tighten cluster grounds.

sixto · #20 01-07-2014, 04:53 PM

If this is a '92 300D, there's an inductive rpm sensor right by the starter.

Sixto
87 300D

funola · #21 01-07-2014, 05:00 PM

Quote:

Originally Posted by sixto

If this is a '92 300D, there's an inductive rpm sensor right by the starter.

Sixto
87 300D

Oops, didn't read his sig. It is a 92. Can you describe the pickup and trigger location?

sixto · #22 01-07-2014, 05:14 PM

This is a picture of a 603.970 but the 602 has identical positions for starter and rpm sensor, the smaller hole in the oil pan below the starter -

Sensor wiring could very well be touching the starter motor case.

Sixto
87 300D

funola · #23 01-07-2014, 05:31 PM

Quote:

Originally Posted by sixto

This is a picture of a 603.970 but the 602 has identical positions for starter and rpm sensor, the smaller hole in the oil pan below the starter -

Sensor wiring could very well be touching the starter motor case.

Sixto
87 300D

Thanks for the pic. Looks like the trigger is on the flywheel? Sensor wiring should be insulated shielded cable. Even if the insulation is worn and the shield (ground) is touching the starter motor case (also ground), it shoud not cause the tach to act funny.

sixto · #24 01-07-2014, 06:26 PM

That's why I hypothesized the ring gear is slipping on the driven plate. Should be able to observe this with the car on ramps. Or fit a flywheel locking tool and spin the crank puley.

Sixto
87 300D

whunter · #25 01-07-2014, 11:13 PM

Quote:

Originally Posted by sixto

That's why I hypothesized the ring gear is slipping on the driven plate. Should be able to observe this with the car on ramps. Or fit a flywheel locking tool and spin the crank puley.

Sixto
87 300D

Not what I am hearing.
A loose ring gear has a horribly unique sound.
I honestly hope you never hear this sound.

.

thebenstenator · #26 01-13-2014, 02:34 PM

Hey sorry for the long time no response. But the last starter's symptoms were that the solenoid would pop out, but it would not spin. I got my starter at O'Rilley's because I had a warranty there, so no charge. When I took the new one out I had it tested at O'Rilley's and it tested fine, but if it is the bendix clutch, how can I tell for sure and prove that it's not working? That seems to me to be the most probable thing.
I'm not super concerned about the tach reading, because it only does that when the starter is spinning, but not turning the engine. If it starts the engine then there's no tach reading.

funola · #27 01-13-2014, 07:45 PM

Quote:

Originally Posted by thebenstenator

Hey sorry for the long time no response. But the last starter's symptoms were that the solenoid would pop out, but it would not spin. I got my starter at O'Rilley's because I had a warranty there, so no charge. When I took the new one out I had it tested at O'Rilley's and it tested fine, but if it is the bendix clutch, how can I tell for sure and prove that it's not working? That seems to me to be the most probable thing.
I'm not super concerned about the tach reading, because it only does that when the starter is spinning, but not turning the engine. If it starts the engine then there's no tach reading.

Did you check the flywheel ring gear? See if the teeth are rounded off or any other anomaly. All electrical connections good?