Hi purchased an 1998 mercedes clk320 and within 10 miles the car suddenly died. After a couple tows and the inability of mercedes licensed mechanics to diagnose mainly due to the ecu not spitting codes I got it home determined it to be a faulty ecu. Opened it up and sure enough there was actually burn marks on the case. I sent the unit off and had to wait a month to receive the unit. Plugged it in and the car run excellent. There were 3 issues abs esp lights remained on, car sometime wouldn't shift to 5th gear and said I had a faulty brake or tail light one was a little dimmer. Three weeks later the car wouldn't start and had all the ecu symptons of fan on high, key turned, all lights and equipment operated, when jumped starter turrn and fuel pump operated. I purchase two donor ecu's and took immoblizer from my original and installed in a new one. When I tried to start the car I have these symptons. see part two
The symptons are:
There is plenty of voltage from battery
If I turn ignition quick there will be a click and almost feel like it is beginning to engage starter. Turned slowly there is no sound. all lights etc work. computer links to scanner but throws no codes. fan is back to normal. K40 and all fuses appear good. new brake switch installed. we tried a number of reset procedures with no results. So here's a few thoughts.
when i turn on the check engine says it is reading the ecu. Is it the key recognition thing and if so is there a workaroung besides towing 100 miles to stealership. could it be a transmission sensor. there are no indicator light on dash that shows linkage position. when I look below for 2 large wires what is procedure. is there something else that I can swap to ecu that also needs to be done. I am hesitant to ship off the ecu to be tested due to time money and all the above. I definately won't be sending to ecmtogo but the module repair in LA

 

It'll only cost you $10, and is something to be checked on a car this age anyway, but try changing the ground cable running from your negative battery terminal to the frame of the car. I had a no start situation and thought I had a parrasitic drain somewhere that I kept trying to trace. Each morning when the car wouldn't start, I would think the battery was dead again since it would just click once, then no furthur response from attempting to turn the key. Each time I reattached the fully charged battery the car would start and run flawlessly, then the next morning it was the no start scenario all over again. Strange reactions from the dash lights (like remaining illuminated even after the key was removed. Sometimes the vehicle could not be shifted back into park. Sometimes the power door locks would work, sometimes not. After day # 4, knowing I had a fully charged battery, I started yanking on the battery cables looking for a possible short, and sure enough, upon closer inspection I noticed a bit of green residue on some of the ground cable strands. Purchased and installed a new ground cable, and have been problem free every since.

It's a cheap try that's an oft overlooked maintenance issue anyway, so you might wanna give it a try. Maybe you'll too get lucky that it's a cheap easy fix? Good luck...

 

but it never starts including when battery is putting out great volts

 

If the battery isn't successfully being FULLY grounded, then it will never start. A partial ground will allow lower power consumption items to operate, but not a high power consumption item like the starter. In my case, what was happening is I was getting a temporarily sufficient successful ground when I reinstalled the battery due to the ground cable having been manipulated. But once the cable "settled back in", then there wasn't a sufficient ground and all I would get is a single click when turning the key, but no starter engagement just as you describe.

If it isn't a grounding issue, then my next step would be to investigate the ignition switch as it is not an uncommon failure part. When you first place the key in the ignition, you should audibly hear a sound like something engaging/disengaging. Do you hear that sound? It's not a faint sound. It's a sound that you can hear very clearly every time you insert the key into the ignition, and again when you remove the key.

 

Yes like the other fellow says and check all the battery connections.
Then crank position sensor.