'75 450SL wiring questions - will not crank

[1990_190e]

Hey everyone! According to the site it's been 5+ years since I last logged in - I thought it was more recent than that but I guess not! I apologize in advance for the rambling I'm about to do.

I'm currently working on a 450SL that my father owns. Purchased it from a friend who had traded for it and planned to put a Chevy in it. We wound up with it after he lost interest and I began work on it yesterday. Car was last registered in 2005. This is the first Mercedes V8 that I've had any real experience with.

The engine that was in it was stuck bad - it had antifreeze in most of the cylinders and the oil smelt of burnt bearing. Purchased an engine from a wrecked but running 80ish 450sl a year or so ago for it. The P.O. had all but taken the engine out; the only thing that was left attached was the shifter linkage and the speedometer cable. I finished pulling it out yesterday and then stabbed the other engine. Today I started hooking things up and repairing a few rat-chewed wires underneath the hood.

I have yet to pull the fuel tank to clean it, and I'm missing the hardware to install the pass. side exhaust manifold, but I wanted to hear it fire. I quickly found out that it won't crank with the key. No power to the solenoid wire. I dripped a bit of fuel down the intake, jumped to 12+ to the solenoid wire and it fired off - with the key in the off position.

I bypassed the NSS with no success. Is there a relay somewhere that could be preventing it from having power in the start position? The ignition switch could certainly be bad but I would assume that it was working when the engine died.

I'm assuming the reason it fired when I was giving voltage directly to the starter was that it was providing 12+ to the ignition post on the solenoid. It only had enough fuel to fire a few cylinders, so I'm not sure if it died from fuel starvation or because I removed power. Does this sound plausible or do I have another issue? The car has electronic ignition. From what I've read most 75's had points. I could be wrong though.

Sorry for so many questions! If anyone has advice I'd love to hear it!

[fonzi]

1975 is a d-jetronic
1980 is a k-jetronic

D-jetronic fuel pumps are supposed to make only about 30 psi while k-jet run about 8 psi. Don’t quote me on this.

It’s rare that a car sitting that long will pump clean fuel for long. Usually the swirl pot filler line or return line that also fills the swirl pot will be clogged. You really shouldn’t try to run the car on its own fuel tank and lines if you have not cleaned them yet.

I suggest you get a fuel pump setup from a k-jet.

I have fried the solenoid wire on a car by cranking it too much. Make sure the wire is t burnt up. Beyond that, it’s going to be some good old fashioned Dick Tracy work on figuring out why the solenoid isn’t getting power when you turn the key.

I think you’ve got a project ahead of yourself, but it sounds like you know what you are doing with cars in general and will be fine in the long run.


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[1990_190e]

Thanks for the info, Fonzi!

I was unaware that a 75 was supposed to be D-Jet. The more I get into this car, the more I think that someone has pieced it together. Oddly enough, it has K-Jet.

The fuel pump on the car is bad and the filler neck has trash in it. Power is disconnected to the pump and the fuel lines aren't attached at the engine - so no chance for trash to make its way into the injection system.

I'm giving power to the solenoid wire at the terminal block on the pass. side inner fender, so the wire running to the starter appears fine. Maybe this car shouldn't have that - but it does. No telling what the harness is out of. I also had to swap the alternator from the engine that came out of it in order to hook up the leads. The 80 engine had a 3-pin plug on connector whereas the one off of the car had a "typical" alternator setup; a hot lead and an exciter wire that bolt to it. The alternator is Bosch #AL69x, which from my research would've come on 82-91 380, 420, 500 and 560 SEL/SE/SEC's. It also requires a 3-bolt bracket as opposed to a 4 bolt.

As for the cranking issue, I'll probably wind up pulling the ignition switch and testing it since there doesn't appear to be a relay before the starter solenoid.

It's definitely a project, and its certainly never going to be perfect, but it should make a decent driver. I'm not daunted by it too much. These cars don't seem any more complicated than my Porsches aside from the fuel system. I have noticed that the distributor cap, vacuum switches, etc. are shared between the Mercedes and my 928's.