Hi Paul

I believe you are missing my point if you want help with a problem with any car you MUST provide us with the tests that have been carried out and more importantly the RESULTS.

Otherwise all we can do is guess at what the problem is.

For example, you say the fuel pressure is OK. I am not saying it is not, but, if we knew how you tested it and what results you got we can judge for ourselves if the results are within spec.

Also this way people could offer different test procedures and then we may all learn something.

As for the coolant temp sensor that has been replaced, this was not mentioned earlier?

Why was it replaced?
What tests were carried out?
What results did you get?

For example, even if there was a coolant temp sensor code in the memory.

The tests procedure could be,
Is there water in the system?
Is the water circulating?
What are the readings on scan data?
Can you back up any discrepancies with a scope?

Then if there is a problem,
Is the wiring ok? (load test)
Is the ECU faulty?
Has the ECU got the correct powers and grounds?

As you can see I have not even mentioned the coolant temp sensor at all yet.

I am not saying this is the correct order or only way of testing because every circumstance is different and your test results can move you in different directions.

I hope you don't think I am having a go at you (Im not) I am just trying to stress the point of accurate/methodical diagnostics.

This is the way people who can help you, diagnose cars, so hopefully you can understand how it is hard for people to form an opinion or point you in the correct direction with the problems you are experiencing with this merc, without any test or results.

HTH
James