240D Solenoid diagnosis - PeachParts Mercedes-Benz Forum

frictionshifter · #1 05-16-2018, 12:13 PM

1979 240D, manual - was starting just fine, and suddenly nothing. New GPs, new injector lines, no reason to suspect fuel deliver otherwise. Firstly suspect was the battery - it was pulling maybe 10V when trying to start, and quickly declining on successive attempts (I used a multimeter). New battery resulted in only hearing the starter spin. After extensive reading on these forums (thanks y'all), I suspect it is the plunger failing to engage in the solenoid. So, given the ample room in the 240D, I pulled the solenoid / plunger from the starter. I suspect the solenoid is kaput, mechanically not electrically. (I had also jumped the starter off the battery and tested its voltage as well, all were fine.)

Take a look at the pictures. The first is the solenoid and plunger. Am I correct in assuming the plunger actually cradles the engaging arm, so it can push-pull? (I've inserted a hex wrench where I think the engaging arm would fit; can't find diagrams to confirm this is correct.)

The second is the engaging arm inside the starter.

The third is the plunger out of the solenoid. Now this is what I think is wrong. I have yet to find an image of a 'new' solenoid where the plunger is not part of the solenoid. It appears almost as if the axial rod in the plunger has been sheered off somehow. Is that possible? [Edit - as noted below, the plunger 'floats'.]

Simple question - do I just replace the solenoid and hope for the best?

Diseasel300 · #2 05-16-2018, 12:42 PM

The plunger on the solenoid 'floats' in the coil body. It is held in place with a rubber cap to keep moisture and debris out of there.

The end of the solenoid plunger should have a pin and a keeper to engage the throwout arm on the Bendix assembly.

The short rod you see in the base of the solenoid is the switch rod.

When you turn the key the following happen:

1: The coil on the solenoid is energized.
2: As the coil pulls the solenoid plunger in, the Bendix assembly is thrown out into the starter ring and the base of the plunger presses in the switch rod
3: When the solenoid plunger is seated and the switch rod is fully depressed, power is sent to the starter motor and it rotates the engine.

From your description of what's happening, the solenoid is working, but the pin and keeper to the throwout arm are missing. Without the Bendix thrust into the starter ring on the flywheel, the starter motor will just sit there and spin.

frictionshifter · #3 05-16-2018, 01:01 PM

I appreciate the quick response, and for clarifying the way the solenoid & starter should work.

I do have the pin and keeper for the throwout arm. I can manually push/pull the arm of the Bendix through the opening for the solenoid. Is it possible the solenoid plunger is no longer pulling the throwout arm?

Diseasel300 · #4 05-16-2018, 02:04 PM

If you push/pull the throwout lever, is it pushing and pulling the Bendix in and out? You should see the gear sliding in and out on its shaft.

frictionshifter · #5 05-16-2018, 03:45 PM

I can't see the gear, as the starter is still on the block. However, I can push-pull the throwout lever of the Bendix. I can hear/feel the gear moving - only about a quarter inch or so.

Can the solenoid die but still send power to the rest of the starter motor?

Diseasel300 · #6 05-16-2018, 08:34 PM

The solenoid has to pull in to activate the switch to the motor. If the motor is running, the solenoid is operating mechanically and electrically.

frictionshifter · #7 05-16-2018, 09:22 PM

Seems like I should just pull the starter and have a local shop rebuild.

frictionshifter · #8 05-17-2018, 01:31 PM

Here is a video, from under the hood, recording when I tried to start it up this afternoon.
https://youtu.be/CmFh5H_Cgug
You will have to forward to 1:49 to hear the start up*. I cleaned up the solenoid, and as noted above the mechanical parts appeared to be functioning. I could push-pull the bendix lever, and reconnected the solenoid throw arm.

* As I wrote in my first post, the car was starting and running just fine. Except for the fact that it has always taken an insane amount of time to glow. The glow light stays on for 90 second easy when cold (like today). THE ONLY THING I had changed before my starting issues were the glow plug wires.
Longer story: The PO had (to my surprise) replaced the loop GPs, but kept the old 'bed spring' wires on. He had also substituted the relay fuse with a plain piece of copper wire

. I put in an 80-Amp relay fuse (though I think it should be 50 AMP), and attempted to replace the wire with some 12 awg insulated copper I had around (didnt work or help). In the interim I broke one of the 'bed springs', and now have only 2 bed springs, connecting 3 glow plugs. It should be enough to start the car? Given all this I am wondering if I am some problem other than the starter.

If its clear I am trying to avoid pulling the starter, that is true. If I should just pull the starter, let me know. If I should solve the GP issues first, let me know.

Diseasel300 · #9 05-17-2018, 03:04 PM

The glow plugs have nothing to do with whether or not the starter engages. It sounds like the glow plug saga warrants its own thread to try to iron out what you have and the best way to go about straightening it up.

The starter definitely sounds weak in your video clip. You could hear when the bendix DID engage, the motor was too weak to spin the engine over. I'd be willing to suspect you have a poor engine ground or poor battery connection somewhere and that's where to start troubleshooting. If you have a poor ground (engine to chassis strap, or chassis to battery cable) its entirely possible for the motor to be functioning correctly, but due to the poor connection lacking enough current for both the solenoid to fully seat and the motor to have any power.

Barring a bad connection, the starter motor may be in need of service/rebuild.

frictionshifter · #10 05-19-2018, 05:22 PM

Had the starter rebuilt at a local shop. Installed it this afternoon. NO GO! Despite my glow plug issues (chronicled elsewhere), the starter barely clicks. Even when I attempt to jump it from the battery, or use the screwdriver trick. I get a click from the ignition area when jumping it (a click that is louder in the car than outside; and which lights the pre-glow lamp).

If the starter were rebuilt properly, shouldn't it at least try to crank the engine? Guess I know where I'll be Monday morning.

Diseasel300 · #11 05-19-2018, 09:25 PM

The click inside the car is probably the glow plug relay if you have the series glow plugs.

The lack of glow plug action and the lack of starter function could easily be due to the ground strap from engine to chassis failing or being corroded to the point that it has a crap connection. Try attaching a jumper cable directly from the engine to the negative battery terminal and see if any of your behavior changes.

If the engine cranks, or the glow plugs glow, you know you don't have a connection between the engine and the battery.

funola · #12 05-20-2018, 11:17 AM

Quote:

Originally Posted by frictionshifter

Here is a video, from under the hood, recording when I tried to start it up this afternoon.
https://youtu.be/CmFh5H_Cgug
You will have to forward to 1:49 to hear the start up*. I cleaned up the solenoid, and as noted above the mechanical parts appeared to be functioning. I could push-pull the bendix lever, and reconnected the solenoid throw arm.

* As I wrote in my first post, the car was starting and running just fine. Except for the fact that it has always taken an insane amount of time to glow. The glow light stays on for 90 second easy when cold (like today). THE ONLY THING I had changed before my starting issues were the glow plug wires.
Longer story: The PO had (to my surprise) replaced the loop GPs, but kept the old 'bed spring' wires on. He had also substituted the relay fuse with a plain piece of copper wire

. I put in an 80-Amp relay fuse (though I think it should be 50 AMP), and attempted to replace the wire with some 12 awg insulated copper I had around (didnt work or help). In the interim I broke one of the 'bed springs', and now have only 2 bed springs, connecting 3 glow plugs. It should be enough to start the car? Given all this I am wondering if I am some problem other than the starter.

If its clear I am trying to avoid pulling the starter, that is true. If I should just pull the starter, let me know. If I should solve the GP issues first, let me know.

You need to remove the bed springs and run individual wire to each glow plug from the glow plug relay, so they operate in parallel.

Your video sounds like the solenoid was engaged electrically and power was applied to the starter motor but did not engage mechanically to the flywheel pinion gear. I can hear the starter motor spinning at full speed (around 9,000 rpm for a good starter). If the starter engaged mechanically, it should spin the engine at a much lower RPM (around 140 RPM with good starter/battery/wiring).

You said your starter was rebuilt in your other thread. Was this video taken before it was rebuilt? Is it acting the same after rebuilding?

frictionshifter · #13 05-20-2018, 01:43 PM

Thanks everyone for the help thus far. This is the second w123 I've owned; the previous was a 79 30TDT I had about 10 years ago, and this forum was invaluable then. The electrical issues I am having this time around are a new page in my DIY book.

I tested for ground this morning, with jumper cables from Battery Neg to Block. Still no start, BUT at least the GP fuse got hot. That is a change from yesterday. No sounds at all this time. No click, not a budge in the starter, and the GPs themselves are not hot. Also tested the Battery Neg to GP (showing about 10V), and GP to Block (showing zero). So I assume I need to pull the engine to chassis ground and clean it up. Two questions about that - it is normal for the Engine to Chassis ground to rub against the speedo cable? I've already cleaned the Battery-Chassis ground and the grounds behind the p-s turn signal, are there any others that should be looked at?

Because of the mixed messages on these tests in terms of voltage, I tested the battery. It is showing 11.7 . It's a new battery, but all this testing and trying to start may have killed it. I'm heading to Autos-zone to get it charged up. Maybe that will help?

My starter video was before it was rebuilt. When I pulled the starter the pinion gear was very loose, so I assumed it was worth the rebuild. With these other issues, I haven't even heard the rebuilt starter spin yet! (Also should have asked the shop to test it before I left!)

I made my own 10 AWG insulated wiring and replaced the bed springs. I keep thinking I messed those up, but I've double checked that wiring a dozen times now, my problems seem elsewhere.

Course of action -
Get the Battery charged up
Test again with Battery Neg-Block jumper cabled together.
If nothing then; take the starter back to the shop for testing.

Diseasel300 · #14 05-20-2018, 01:55 PM

11.7V is a *DEAD* battery. No wonder the starter won't crank.

Fix that ground strap. No it shouldn't be rubbing on anything.

If you have the pencil style glow plugs, 86 the bed springs and make sure all of your plugs are wired together. Use stranded wire that can handle 50-60A. #10 seems a little light.

When testing next time, use a jumper cable (hopefully #6 or bigger) and clamp solidly somewhere on the engine block and clamp the other end directly to battery negative. With a charged battery, you should be able to get the plugs to glow AND the starter to crank.