'72 280SE Won't Start
 

I'm going out of my mind trying to figure out why this thing won't start. Here's the deal... It's a 1972 280SE with the 4.5 M117 V8. It was running great the other day, but since the engine was quite sludged up, my dad decided to clean the engine with some degreaser and water. Afterwards, it wouldn't start. I know there's nothing wrong with the FI, the injectors are spraying just fine (I took one out and watched it spray). So I figured it was the ignition system, though it seems to be getting a pretty healthy spark out to the plugs. I'm guessing this has something to do with moisture since it was working great before it was washed. Could moisture in the distributer be making the spark too weak or messing up the timing? Is there perhaps some other system that could be affected by water? I'm kind of unfamiliar with Mercedes engines, so I'm somewhat at a loss here.

Take the distributor cap off and make sure it is dry. If not wipe it dry and you can spray some wd40 in it.

Are you sure it's getting fuel? Can you hear the fuel pump (near the gas tank) run when you turn your key to the on position? If you can't hear the familiar hum of the fuel pump with the ignition key on (but without trying the starter), then I'd check the fuse for the fuel pump. I had a friend with a six-cylinder 280SE that wouldn't start, and it turned out to be a corroded fuse. Good luck.

Joe Bauers

still no go
 

hmmm.... well, I went ahead and tried the wd40, no luck. This time I actually checked the fuel pump, it's goes on when I turn the key. I actually took out an injector and watched it spray fuel while the engine turned over, and I can also smell unburned gas, when I turn it over, coming out of the exhaust, so I'm positive that it's getting fuel. I figure it has to have something to do with the ignition. I took out a spark plug to make sure that it was firing, and it was. Like I said, it seems like it might be a weak spark though. Would it be possible that the plug would spark in outside air but not under compression? I'm pretty sure the timing is fine unless merceded engines just occasionally jump the timing like 80 degrees off, the distributer is very tight, no movement there. In any case, thanks so much for your guys' suggestions, I appreciate it, any other ideas you might have?

If the engine was pressure washed, chances are good something got wet that shouldn't have. When ever I clean my engine I only use hose pressure and let the water run where I want it to. So it takes a bit longer to cut through the crud, no biggie. If your Dad did use only hose pressure, he may have watered something accidently, it happens. Good news is it should dry out.

Make sure there is no moisture on the inside of the distributor cap or rotor, not sure if the trigger points can be affected by water or not, make sure there is no water under the plug resistors cause spark to go to ground. Same for the coil wire ends. I think it is all related to the washing.