Wondering if anybody here can help? I attempted to start my 900SL today after a full strip down paint and rebuild, and the engine wouldn't turn over. At first I thought the battery was knackered, so I replaced the battery. When I tried to start it with a new battery I had the same problem. When I turn the ignition on, I'm getting a large voltage drop across the battery. Disconnecting the plug to the fuel pump/low level sensor seems to cure the voltage drop, so I'm suspecting it might be a faulty fuel pump. That said, I can't see how a little fuel pump can drain two batteries so quickly. It's like a dead short that's not blowing a fuse Any ideas anybody? View attachment 38543
Even with the fuel pump disconnected it should turn over (does the pump run?) , does the starter solenoid operate? If it doesnt then most likely culprit is the 2way plug into it, lousy design, mine is cable tied in place. Put a meter on it and see if you get a voltage on the starter side when pressing the button. I've proved the starter by putting a jump lead from the motor terminal to the battery +ve. Also if you have repainted did you clean off the paint/powder coat from the earth points? Mike
The starter circuit is all OK, and the earth points are good. I did actually start the engine by jumping off my car battery, but only ran it for a little while. The pump does run but it doesn't sound right, I'm thinking that might be because of the low voltage. My problem is trying to figure out what's draining the battery before I even attempt to start it. It's like a really bad dead short, and the time it's taken to find the fault has flattened the new battery. I'm thinking it must be something I've done wrong, but I've had all the wiring out and can't find no fault. Like I said earlier, the only thing I did find was a fault with the fuel pump, but the pump doesn't draw enough current to flatten the battery so quickly. Got the battery on charge tonight hopefully if I get time I'll have another go tomorrow. Cheers Rich
Deadweight makes a good point about scraping earth points and I would do same basic battery direct check as he suggested - live (carefully) onto starter terminal and then an earth to engine crankcase obviously in neutral. If this turns engine over then you can work back from this to see where the problem is and it's most often within the live route as there are far more 'connections' to fail rather than the basic two earth leads.
have you had the low level sensor out of the tank wiring on mine was damaged slightly and surprised it hadn't shorted worried considering where it is assuming its the same as mine as that's an ie model
Will check the low level sensor today. Thinking about it this morning, I suspecting this simply just a battery problem. There's no short circuit because no fuse's blowing. I'll kick myself if it is the battery. Thanks
Your post got me thinking, made me realise it wasn't a dead short. Turns out it was the battery. Was in to much of a hurry to get the engine running, and I didn't charge the battery long enough. I automatically assumed it was something I wired wrong, and ended creating a load of work for nothing. Anyways, engines running everything good. Cheers Rich
