2004 E320 wagon intermittant starting
 

My wife's wagon recently started acting up.
It intermittantly refuses to start maybe once out of 20 tries. The other 19 starts are perfect half crank engine starts.
On the bad starts there is only that clicking sound. The sound like your battery is dead. So I replace the 5 year old battery.
But the problem still exists.
Is there a common problem on there 211's ?
Like faulty ignition/key switch or transmission switch or something?
Any help would be appreciated
jz

I forgot to mention that when the battery was changed we checked all electrical connections to the battery and starter/solenoid etc

If it starts in the morning (cold engine) but acts up during the day it could be the Crank Position Sensor. Common problem.

A bad crank position sensor will cause it to crank but not start. Trying to start and only getting a click means the starter is on its way out. I'd replace the starter.

Thanks Pawo,
That's what the indie mechanic thinks too- starter.
So he's putting in a new one today.
I had CPS problems with my 164 CDI. Engine would just die while driving.
It was replaced under warranty.
jz

I believe there is a small relay that the computer uses to activate starter, i would replace that first if intermittant, its in fuse box

Before you throw any parts at it, check the starter cable connection at the body side. The lug where the cable connects can become corroded. I've seen it happen many times.

If you're not sure what I mean I'll try to explain. The main battery cable (+) is connected to the front pre-fuse box, located beneath the front passenger's footrest panel. The other side of the pre-fuse box (where it passes thru the body) is where you want to check. You'll need to get underneath the car to find it. Just follow the big cable from the starter. :)

Thanks gentlemen.
I will follow your advice.

I am an idiot.
My wife has been unable to start the car a half dozen times in the last month. But after she sits for 10 minutes or so the engine will start.
She describes the sound as a clickety click sound (like when you have a dead battery). I asked if the engine is turning over and wifey says no and I believed her.
I drove the car and started and restarted the engine 100 times and never had the problem.
Finally today it happened to me.
However, it is not the clicky sound at all. The engine is turning over and cranking and cranking but will not start. I sat for a few minutes and it started fine.
I had a similar problem a while ago with my ML CDI. It turned out to be a faulty fuel pump.
Any insight or comment would be appreciated.
thanks
jz

The faulty relay is out because the starter IS engaged and cranks the engine.
Could it be the dreaded crank position sensor ???
Will a faulty CPS send up a fault code?
jz

Take it out heat it up with hairdryer while measuring set to ohms, heat it up to around 200 degrees , if bad circuit will go open, or just replace crankshaft sensor

Thanks yes.
They are cheap enough.
On peachparts the MB SPS id $288.
The bosch is only 128.
I thought it would be much more costly.
I bring it in tomorrow.
jz

Final diagnosis is a bad crank sensor.
Had it bench tested to confirm.
Thank you guys for your help on this.
These intermittant problems are tricky to solve.
jz