Hello all,

I am only new here but i have been researching for last few weeks a current problem on 2009 skoda octavia 1.9tdi 118k miles on clock,it starts first turn when cold all the time but when warm will not start unless untill cools down,firstly i thought may be a fuel problem so changed fuel pump but no fix,i disconnected the coolant temp sensor and starts all the time so i changed coolant sensor no fix,i read about remapping it to copy the cold start to hot start to trick icu but after speaking with a company they said my problem is mechanical and not software so next step i got crank shaft sensor changed but again no fix,after alot of reading i dont know if to change cam shaft sensor or just change the starter,there is no error codes coming up,i have read about the starter issue and it seems to have fixed some.Anyone any advice of success fixing this?i have spend alot of money and no fix yet and getting extremely frustrating :( apart from this problem i have had no issues whatsoever with the car,timing belt was done at 80k miles and serviced regular.

Are you absolutely sure your car's battery has enough capacity to spin the engine fast enough?

 

As I understand, when cold, the engine will fire at low RPM but when hot the starting RPM required is higher.

 

Try jump starting when the engine is hot to confirm.

1 minute ago, MicMac said:

Are you absolutely sure your car's battery has enough capacity to spin the engine fast enough?

 

As I understand, when cold, the engine will fire at low RPM but when hot the starting RPM required is higher.

 

Try jump starting when the engine is hot to confirm.

Hello,

Thanks for the reply,i checked the battery last week by jumping it with a power pack but still no start also the mechanic tried to start off a different battery today when warm and again no luck.

That still leaves the engine crank speed in question, check the wiring/connections from the battery posts onwards as far as you can i.e. starter/solenoid.

 

It could be a tired starter motor or just a bad connection somewhere.

2 minutes ago, MicMac said:

That still leaves the engine crank speed in question, check the wiring/connections from the battery posts onwards as far as you can i.e. starter/solenoid.

 

It could be a tired starter motor or just a bad connection somewhere.

Ok,if was a bad connection would it not be present even on cold starts or also when i have disconnected the coolant temp sensor?with the coolant sensor disconnected it starts no problems hot or cold,i was hoping replacing the crank shaft sensor yesterday would have fixed it but i had read about the starter problems beforehand.

IF there's a poor supply through the wiring it will only pass so much power to the starter motor, starter motor may spin fast enough to start cold engine but not hot.

 

Disconnecting the coolant temperature sensor fools the ECU into thinking the engine is cold so it starts.

 

Boosting the car's battery in this scenario by jump starting is unlikely to help as no matter how much power is available it cannot be conducted due to a poor connection/wire damage, eventually the weak link will burn.

1 minute ago, MicMac said:

IF there's a poor supply through the wiring it will only pass so much power to the starter motor, starter motor may spin fast enough to start cold engine but not hot.

 

Disconnecting the coolant temperature sensor fools the ECU into thinking the engine is cold so it starts.

 

Boosting the car's battery in this scenario by jump starting is unlikely to help as no matter how much power is available it cannot be conducted due to a poor connection/wire damage, eventually the weak link will burn.

ok i get you now,is there a way to test the starter without replacing?thank you

Maybe VW dealers can test motor RPM, unlikely*

 

Check all wiring/connections are good not just visually, remove heavy gauge connections and clean/inspect could just be corrosion, reconnect securely testing for electrical resistance.

 

Other than that all I can suggest is removing the starter motor and checking the condition of the brushes and that it rotates freely.

 

* With a diagnostic tool plugged in you should be able to log engine RPM when trying to hot start.  I don't know what the required hot start RPM is, maybe someone else can advise.

Edited 27 June, 20205 yr by MicMac

2 minutes ago, MicMac said:

Maybe VW dealers can test motor RPM, unlikely.

 

Check all wiring/connections are good not just visually, remove heavy gauge connections and clean/inspect could just be corrosion, reconnect securely testing for electrical resistance.

 

Other than that all I can suggest is removing the starter motor and checking the condition of the brushes and that it rotates freely.

Thanks for the advice,will look at that next so.

On 27/06/2020 at 16:52, ste1234 said:

Thanks for the advice,will look at that next so.

Did you ever find a fix for this?

Also check the earth cable from the battery negative to the body.

Check too the cable itself at the battery end. On previous models it was found that black wire corrosion had been found running down the inside of the cable from the crimp connection.

Edited 2 September, 20232 yr by pikpilot

Check the fuel pump relay. Give it a tap while trying to start. Sorry can't tell where to look.

Just reading this as my wifes car has a similar thing, also sounds rough, but I think that's something else.

Mine turned out to be the starter motor