Hello,

I really need some advice,i have a hot start problem on skoda octavia 1.9 tdi 2009,i have changed coolant temp sensor,crank shaft sensor,fuel fitler,and now put in reconditioned starter but the problem is still present :( the mechanic thinks it is worn injector seals and not getting enough compression when warm/hot so will not start however if i have the coolant temp sensor disconnected it starts hot or cold,my question is if worn seals how would disconnecting the coolant temp sensor suddenly fill the gap where seals are worn and possible letting air in?if the problem is the seals should it not start when warm/hot regardless of sensor disconnected?apart from hot start the car runs prefectly fine,the problem came into it 4 wks instantly there was no lead up to bad starting whatsoever,starting cold it turns first turn,it has 118k miles on clock so fairly low milage.

You need to log engine RPM during cold and hot starts for comparison... and change mechanics, he's loving you by the sound of things.

 

The logs will show:

 

1. If there is a difference in cranking speed.

2. If that speed is sufficient to meet hot start requirements.

 

It would help f you could disable the fuel pump/injectors whilst logging to prevent the engine from starting and so provide more data to work with.

 

Assuming you don't have the gear to do this and you aren't leaving it with a mechanic, only the hot start RPM is going to get logged.

 

Just out of curiosity, find a reasonable hill and try bump starting it, obviously hot.  Does it start okay or do you still need to disconnect the coolant temperature sensor?

This is actually a different mechanic lol he advised me not to change starter but i was convinced it was the problem,i just dont understand if it is the seals then how would disconnecting the coolant temp sensor by pass the compression problem if seals are damaged?are you thinking the battery maybe faulty when suggesting the bump start?i did check battery and tried to start with power pack when hot but no luck

At the risk of repeating myself, as I have already explained, either the engine is not turning fast enough for a hot engine start or the ECU does not believe it is.

 

As was said if it isn't turning fast enough then the battery, starter motor and cable connections could each be the problem or contribute towards it, if it is turning fast enough but the ECU is not seeing that then the crankshaft sensor is the suspect.

 

I already explained how you could wire a relay to fool the ECU that the engine is warm but not hot and hence remove the stupid requirement for rapid cranking when hot, without the stupidity the PD engine will start hot or cold with a lazy 1/4 turn on the starter or bump start.

 

The mechanic is clueless if you have asked him the question and a light bulb did not go off in his head.

Jr I have changed the starter on Friday, the battery has been tested, crank shaft sensor was changed last Monday, I have took any advice on board and followed through. 

Just make up a relay circuit to fool the ECU and forget all about the from then on "non problem"

would that pass nct/mot test yearly though?

Nobody would know that its there, it would only operate when cranking the engine, you are not modifying the emissions or anything, just allowing it to start.

30 minutes ago, J.R. said:

Just make up a relay circuit to fool the ECU and forget all about the from then on "non problem"

is that not masking a problem though?how did the problem suddenly come into the car 4 wks ago.I contacting a re-mapping company and they said the problem is mechanical and not software.