The car in question: my girlfriend's '79 240D automatic.

It's been having issues starting since we've gotten it. I determined it was a number of issues, including air getting into the fuel system via a bad IP seal to injector hardline #4 (still have to fix that) and a starter/solenoid combo going bad. It's the latter that's giving me real issues.

I got a rebuilt Bosch turbo starter from -insertobvoiscompanyhereinBellinghamWA- and spent a good 5, 6 hours finagling the old one out and getting this bad boy in. Near the end, I was having difficulty wiring-up the new starter, mostly not remembering which wires go where. Saw this by arching and bad sparking when touching the battery terminals with the connectors, meaning there was obvious load on the system. Called my friend over who also is a dieselhead to help me, and we finally got it hooked up and started with no issue (other than the air leak making the turnover difficult).

It went all south last night. I drove her car to college to stretch its legs. Started up fine at the house. Didn't even engage when I tried to start it after class a few hours later. Turn the key, wait for the glow light, turn to fire the starter... -click-. Hit the starter and solenoid a few times, kept trying. Nothing. Called AAA and they sent out a local tow truck. Told him my issue, so we both started messing with it. Here's what gets me confused: He took out a metal rod and when he touched the positive terminal of the starter and the support bar for the air cleaner housing, it started right up. Now, I now you can normally bypass the switch by jumping the connection between the positive starter terminal and the small terminal for the ignition switch. But he just grounded the system. I thought the starter grounded itself to the block...?

So, tl;dr version: Is the starter not grounded properly?

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- 1979 W123 240D 4-speed, 390k miles

could be as simple as loose conections

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Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"

The starter indeed grounds through the engine block BUT there is a ground strap from the block (usually back where the transmission attaches) to the chassis. This strap is under the car where it can get dirty/rusty/damaged. Check this strap and its bolts and make sure they are clean and tight. Then as Philly says, check all around the battery and the starter for loose or otherwise non-optimum connections.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

x2 on loose or bad connections. Loose or corroded. Sometimes an auxiliary ground wire from the battery to one of the starter mount bolts will help.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Didn't know there was a grounding strap down there...I'll take a look when I get home from work. Easy to spot?

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- 1979 W123 240D 4-speed, 390k miles

Easy for me, maybe, but I know what I'm looking for. If I were looking for the first time it might be a different story. Here's a picture of my '96 E300D, taken during a starter motor operation. The ground strap or wire is pretty obvious. I don't know how different your '79 is, I've never seen one underneath.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Really do not understand what he did. I would expect sparks flying when he touched the positive terminal of the starter to chassis using the metal rod. I am not sure it is the grounding strap.

You should have asked him what he did.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

The only way I can possible think of, how this is possible is if the glow plugs were upgraded to pencil style from loop and the ground strap was connected to the last pencil plug. This would in theory add 12v to the block.

I would personally remove the battery and battery box, and get a better view at the wires connected to the solenoid and confirm everything is hooked up properly and none of the wires touching.

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I'll take a look at that too; the plugs are the upgraded pencil-style. I don't recall if the PO(s) removed that old GP ground or not.

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- 1979 W123 240D 4-speed, 390k miles

If my eyes are not dodgy in reading

Im seeing that someone connected the positive thick battery wire to the starter to an engine ground - this will cause massive sparks/welding/fire as you are dead shorting the battery.

By connecting the starter small and big wire terminals together you are bypassing everything and the starter motor is energizing, which is proves that the ground is good - that motor sucks north of 400 amps when turning that high CR 4 cyl diesel. A bad ground would cause the motor not to operate at all in that case.

What you have is low amps from the key/NSS to the starter solenoid, you can test this by using a sealed beam headlamp or a working H4 bulb with both elements connected together combined to give a load of about 10 amps. If you test that the solenoid wire can immediately illuminate the beam to full bright your system is good, if its faint or orange glow, resolve it.

You might also want to add a starter relay (aka hot start relay) to boost the system.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

So, just to be clear, the main wire from the battery comes into the top terminal, and the wire to the alternator also connects to that top terminal. There are two small wires; a purple one which I assume is the direct line to the starter, and a bypass line for the glow relay. Nothing connects to the bottom (ground) large terminal.

Right...?

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- 1979 W123 240D 4-speed, 390k miles

Not sure what you mean by the 'bottom'ground' large terminal'.

As I see it, all the AAA guy did was provide a path for the current to flow from the positive terminal to the negative terminal while running thru the starter. In other words, grounding the small starter terminal wire mimics the engagement of the ignition switch, activating the solenoid.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

When I changed put my starter on my 1978. There was the large wire that runs to the battery and a group of smaller red wires that connected with that cable to the top nut. The small Phillips screw held one red wire that I assume goes to the ignition and the bottom nut held nothing but the braided wire that goes to the starter motor. I never had a purple wire. Its possible someone has been tampering with the wires.

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Talked with my brother just now. He works on forklifts in a local lumber yard that've had this same issue. Apparently, the starters can ship with residual charge in them. he just hooked a separate ground cable up to the starter and the block to drain it. Removed that cable, car fired right up.

Interesting....

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- 1979 W123 240D 4-speed, 390k miles

If the AAA guy grounded the lower solenoid terminal that has a braided wire going into the starter windings then your starter is a bit corroded internally or the brush pack holding screws are stripped or corroded. They are the ground.

The solenoid takes it ground from inside the starter windings for the pull coil which then bridges the high current contacts in the solenoid for the motor to work.

You need to remove that starter and overhaul it.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)