1997 (W210) E320 ignition cuts out

[chamberlaini]

I have a 1997 (W210) E320, which has run fine for the 8 months I have had it. However last Monday driving down the motorway, it just stopped. The ignition failed. After abiot 30 mins or so of trying to start it, it restarted, and stayed running for a further 7 miles. Again another 30 minutes later it restarted, and got me 20 miles before stopping. I fanally got it to the dealers, who frankly did not have a clue. they tried telling me it was the fuel pump before they even saw the car. This theory was impossible as I was running on auto gas at the time. The second and subsequent times I was on petrol and it did the same. When the finally got it to the shop they verified it was the ignition (or something to do with ignition) as I was not getting a spark. Then they tried to tell me the reason for this was due to the catalysic converter rattling sugesting it had craked. They then replaced the main engin ECU, which did not solve the problem. They say the ECU is not giving any fault codes, and dont know what to try next. this is the dealer saying they dont know what to try next, which is anoying seen as they charge £76 per hour and have already spent 12 hours on it.
The manager can not tell me what they have checked. When asked what inputs are critical to the ECU to produce a spark again he didnt have a clue. Surely the ECU/ignition system will work to some extent with just a few basic input, eg crankshaft sensor etc

Can any one help.