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@isetta thank you for the kind words and happy to be here and of help, as for the injectors I'll try to fix them and if i can't then I'll have to buy another ones . it's the weekend so I'll take them for repair on Sunday . (it seems that I can't edit my old post ) @Tdci-Peter Well what can I say once I read your replay I run to the car and performed the leak-off test ( i have just finished ) and it revealed the faulty injector, so Thank you for the suggestion and the explanation. For the startup pressure measurement it was not very accurate because i just used an ELM237 clone and the refresh rate was low, but it was enough for the long periods. as for the repair-shop you are right, the first one that i took them to claimed that he have the tools for it but apparently he didn't ( cause he messed up my friend's Focus with 1.8 engine it came running to the shop and left towed after the service ) and if i recall correctly the injectors on the 1.8 are different and have no other compatibles while the 1.4 ones are more common ( because of PSA). Now back to the leak-off test, I did it with the elimination method since i didn't have enough pipes and plugs ( each injector has a Y junction on the leak outlet ) so i collected the leaked fuel from all the injectors once it was cold and once it was hot for two minutes each time, and the when-hot-quantity was three time that of the cold one, then i started eliminating the first injector by connecting it back to the car leak pipe while the other three are under test ( their leak is collected in a bottle ), then 1 & 2 are eliminated and 3 & 4 are under the test and so on. at each time observe if the leaking flow changed too much from the last test. but the results were too obvious and showed that the second injector was leaking too much when hot. and i didn't bother with the rest of them . probably I ll just take this one for repair cause the last repair costed more than the price of two injectors. all I needed for the test was two pipes, a plug and a bottle , a pipe from the tested injectors to the bottle and the other pipe with the plug just to close the other outlet from leaking. thank you all for the help .

You have two suspects here the temp sensor and the thermostat , but i would say it's probably the thermostat has failed and it is constantly open which lets the cooling water to circulate in the radiator and gets cold ,normally it should be closed until the temp reach a certain degree then it opens next when the engine heats up more the fan kicks in to help.

Hi all, i have the mk7 with 1.4tdci and i'm facing the same problem but i think i have narrow it down to the injectors, seems one of them is faulty and when it heats it gets stuck open and drops the pressure then the car dies, I can start the car normally when it's cold but once it heats up I can't start it again unless i use a starting fluid ( i use insects spray ) or let it cool down for hours; but when i was experimenting with it i tried cooling down the suspected parts with water then trying to start the engine again ( before that i used a scope to inspect the signals and all was fine ) so i tried the crank,cam sensors, fuel temp, the high pressure pump, the fuel rail ( in case it had a crack ) and no difference, then i tried the injectors and it worked , so if the car is hot and it doesn't start i pour some water on the injector for a while and it starts immediately (although other parts are still hot ) . I have checked the waveforms and voltage levels when the car is starting ( once it's cold and once it's hot ) and didn't see any difference except for the fuel pressure which is 4000PSI and can go up to 6000PSI when the engine is cold, while it stays under 1200PSI ( since the startup time is short when the engine is cold I removed the injectors' plugs to prevent the car from starting while i log the pressure readings ) I could clearly see the effect of cooling the injectors as the pressure start to rise up ( from 1200PSI to 1500PSI then it starts ) but I'm still not sure i rolled out : -the starter : because of the cranking RPM was same hot or cold. -the crankshaft and cam sensors : because the wave forms are the same ( and the car starts with a starting fluid even when hot and runs fine which means they do work when hot ). -the fuel pressure, flow regulators + the pump : also the wave forms were the same and i tried cooling them down but got no results ( but they are still suspects). -the ecu blocking the injector waiting for higher pressure : because at first fooled the ecu by rising/lowering the voltage on the pressure sensor line with no difference, then probed the injector lines and there was a firing signal ( it above 100V since they are piezo ) even at low pressures while the car is hot. - the fuel evaporating in the pipes and making bubbles : also because it runs fine once started with starting fluid and keeps running ( where did the bubbles go ? ) to confirm my suspicions I'll take the injectors to a repair-shop and see how it goes from there ( I had taken them before only to get worse results ) so if anyone have any advice or notes you are welcome to point it out , and I hope this helps you @wightstar . should note that i have poured the water on the engine while the "car cooling water reservoir" was open from the start ( when it was cold ) first to avoid any effect of the vapors condensing quickly and secondly to not burn my self opening it when the engine is hot ( done that once and burned my arm ) and i think someone will complain that it's not a good idea to pour cold water on hot metal but if you have this problem for a while you'll be ready to push this car off a cliff into the sea.