1987 Mercedes 300 SE - Sluggish Starting Despite Loving Care

You may have a battery that's running out of business. Typical simptom after some hours stopped and with cooler ambient temperature. How old is it? There was a time the batteries used to last for 5+ years. I've seen recently that if you have one with more than three years and is experiencing slow starts, replace it. You can actually take your car to a shop that is able to connect it to a tester that is no more than a load bank simulating starting current draw and measuring tension. It will show you if it is compromised or not. But I bet it is...]Regards.

89K miles is just getting warmed up!

When you say sluggish, do you mean slow to crank or turn over?

Or does the engine crank over normally, but the car fails to start right away?

The former may just be a battery. The latter may be a number of things like a weak fuel pump or clogged fuel injectors.

You may need deeper diagnosis to check compression or maybe the spark plug wires are bleeding off energy. I don't know if that car has points or electronic ignition, but chances are it has a distributor cap and rotor that should be checked and replaced.

Just some thoughts.

Thanks cranks over but does not burst into life!

Your comments are appreciated,what about running through some injector cleaner?

Thx

For a gas engine Techron is a good choice.

When the car is warmed up and running, how does it respond to increaded throttle under load?

You might also want to try this trick. Park the car running at night where it is very dark. Pop the hood and look to see if there is any blue electrical arcing around the plug wires and distributer. This works best when the humidity is high. You could try a bottle of water spritzed over the engine, but it needs to be a fine mist, not a stream.

If you see arcing, then the cables need to be replaced. If the cables have never been replaced you probably should do it no anyway.

PLUGS? It's a gas engine?

Hi Petrol engine yes new plugs fitted Bosch....

Hi There, some things that may help...

1. You or someone should check the coil/output power going to the plugs to fire

2. You say it's turning over - does it seem to be at the same constant as always, or does it sound like it's a little slower than it used to - could be you need a new starter to ramp=up with

3. I know you bought the Bosch plugs, but you may want to consider some NGK plugs for hotter firing - it helps in colder times

As someone said, your mileage is nothing - you still got a youngster for a car!

Good Luck!

If its fuel injected, check the fuel pressure at startup. You could be losing prime or having some other fuel problem.That could cause slow starting after it sits for a while. If you're worried about wear out do a compression test. I'll bet it will be fine if you have always kept up with oil changes. I know the diesels are real sensitive to cranking speed when cold, but I haven't dealt with gas engine Mercedes.

I forgot to mention vacuum leaks. That can definitely cause hard starting. If your vacuum hoses are original, you're bound to have some leaks by now. Look for little cracks around all connection points. If you change some hoses, watch out for cheap ones not being rated for gas or oil. You'll be changing them again if you don't watch out.

You did not mention the fuel filter. If it is still original, it could be restrictive by now. That engine should be good for 3x that mileage before problems develop.