missfire and temp sensor issues/smoke

Hi,

I have a 55plate 2.0 tdi which has had a string of issues that I need help with.

Over the past 18 months it has had 2 Dual mass Flywheel failures, on the second failure I spoke to the flywheel manufacturer LUK technical dept who advise that missfires cause the flywheel to fail.

I was aware of a murmer/missfire at idle and am thinking that this may be the route of my problem. There is also more smoke (sooty) from the exhaust than I would expect, even under light acceleration.
I have read about issues with injector looms, so replaced it as a precaution. I have tested the injector resistance both hot and cold which seem consistant between the 4.
Since owning the car the dash temp gauge is hardly reading 50 deg C even after prolonged runs, I am starting to wonder if it is running rich as it never gets upto temp?
I tried swapping the sensor at the back of the block but it does not seem to be related to the dash sensor, Are their other water temp sensors relating to the gaugeI should be looking for?
I have also noticed excessive soot deposits in the intake down stream from the EGR inlet port.
Any help would be much appreciated, I really like the car
I tried

misfire is detected by crank sender returning the inductive/hall effect signal from the flywheel, the misfire is detected by uneven crank rotation due to combustion bounce hence the rpm differs from the pre map and the tdc reference point will vary because its misfiring so expected rpm will be out and misfire detection occurs

smoke indicates blockage or air leak under load

check all the intake pipes and vacuum pipes also remove the inlet manifold and check the change over flaps are in order plus the vacuum unit

check fuel balancing across injectors and check for excess soot in the fuel

coolant sender should be high voltage from cold start dropping uniform as the heat increases

so stone cold 4.5 volts and normal operation around 1 volt

or use vcds compare coolant with fuel temp and ambient temp from cold

soot will build in the inlet thats unavoidable with egr regulation but check there is no excess egr flow or blank the port to compare

finally gas test to see whats coming out the exhaust

firstly thank you,

Can you confirm I have located the correct temp sensor related to the gauge?
The one I replaced is at the back of the block which has a plastic clip retaining it, grey base 2 pin with o ring seal.

yes thats the coolant sender

damn,any ideaswhy the guage would read so low?

Just stripping all the intake parts from the turbo to the engine, including the inlet manifold, there are no change over flaps on the intake

ok thats fine you have the earlier engine 140 bhp make sure the vacuum pipe to the turbo are all ok and not flat also remove the turbo pipe and check its not split or splitting

check the reading in address 01 engine electrics and address 17 dash via measured value blocks with vcds

if they are the same as the visual reading on the temp gauge (50 c) then look for a mechanical fault by comparing the upper and lower coolant pipes in case the thermostat is stuck or broken away inside the plastic housing or use a thermometer to check what the actual engine cooling temp is

Ok, stripped all of the intake to try to find any sign of an air leak, also removed the intake manifold, unfortunately nothing found and the murmer on idle is still apparent, getting very paranoid that this could lead into another failure of the dual mass:(

How do I check for injector ballance?

Also can you advise the best method of checking for soot in the fuel?

Is there any other tests or checks worth doing?

On the temp guage front I removed the thermostat housing expecting to see the thermostat stuck open, all seemed ok, guage still reads about 52 deg c
I do not have a vag com just a basic code reader so unable to compare temp readings, I will test hose temps but I am sure the engine is at correct operating temps even though the guage tells otherwise.

Any assistance is greatly appreciated.

I would change the stat just to make sure

Have you checked the intercooler for leakage?