diesel warm start problems

[andyh12345]

I have searched the forums & this seems to be a common issue, but I haven't found a definitive answer to it

'98 1.9 SLX TDi with 120k

starts fine when cold, but when starting warm - particularly when just slightly warm, & also when the engine has only been off for a few minutes - it cranks & cranks with noticeable shaking without starting. it does always eventually start, but it's a pain

it has recently had a new battery & the problem bizarrely seems worse since

any ideas much appreciated!

thanks

Andy

[ckrisrok]

I had a similar issue on a passat R reg.
It turned out to be the temperature sensor.
Have you checked for any fault codes. 

[andyh12345]

sorry I haven't responded sooner, have been away all week

I have a friend who is going to lend me a vag-com cable & I'll see whether I can get some error codes out of it

[Crasher]

This is a very common issue with this engine. You may find it has no fault codes stored. One solution we have found is to recode the ECU for automatic transmission. If this helps then a new starter motor often cures the fault which is down to the engine cranking over below the MAPS start threshold. Sometimes a new starter motor will not help. A diagnostic aid is to (once the codes have been read and saved) disconnect the coolant temperature sender when hot and see if this allows a quick hot start. If it does the problem (we have found) is in the ECU’s programing, the MAP so to speak and unless the software is re-written to fill a strange hole in the fuelling MAP at low RPM, you cannot cure this issue. Recently we had this issue afflict a 2000 Octavia TDI we fitted with a new engine. The only cure we could affect was to wire in a 5 pin relay with a resistor that was triggered by the starter motor. When cranking, this relay flicked over to the resistor which gave a reading of a cold engine and allowed the vehicle to start as it should but as soon as the starter was released, it flicks back to the sensors correct for temperature resistance. So far this has worked well and not given any fault codes. There is a propriety Italian made system that is plug and play for this solution and it costs about £150.

[s.mate]

Hi there, this is really getting on my nerves, I have a Passat B6 1.9tdi, over 100K on the clock, recently it developed a problem, It won't start when the engine is hot. Cold start is good, starts at first click but after driving few miles and then if I stop the engine, it won't re start, but again it's not the case always, only some times. Because of this occasional problem I can't take it to garage and show them actually what is happening. Does anybody had the same problem? and sorted or anybody know why? please help.

Thanks in Advance

[andyh12345]

here's how I fixed it in the end:

https://www.vwaudiforum.co.uk/forum/showthread.php?124470-TDi-warm-start-problem-fixed!

[johnb48]

I have the same warm start issue, starts first time when cold but a short or long journey and it churns away for 5 secs before starting
Golf mk5 04 reg 1.9 TDi
AM i right in thinking if it was the mass air flow meter or enging temp sensor then it would show up on the fault codes ?
because i have no fault codes
so wondering if the relay will fix the issue ?
Number 109 ECU Relay / Fuel Pump VW Audi Seat Skoda Diesel Meyle Germany | eBay
Thanks John

[Crasher]

Good luck trying to fit that relay, that does not fit the Golf 5....People have become obsessed with this 109 relay crap, it can also be 30, 32, 460, 449 etc etc.

[Doctle Odd]

This is a very common issue with this engine. You may find it has no fault codes stored. One solution we have found is to recode the ECU for automatic transmission. If this helps then a new starter motor often cures the fault which is down to the engine cranking over below the MAPS start threshold. Sometimes a new starter motor will not help. A diagnostic aid is to (once the codes have been read and saved) disconnect the coolant temperature sender when hot and see if this allows a quick hot start. If it does the problem (we have found) is in the ECU’s programing, the MAP so to speak and unless the software is re-written to fill a strange hole in the fuelling MAP at low RPM, you cannot cure this issue. Recently we had this issue afflict a 2000 Octavia TDI we fitted with a new engine. The only cure we could affect was to wire in a 5 pin relay with a resistor that was triggered by the starter motor. When cranking, this relay flicked over to the resistor which gave a reading of a cold engine and allowed the vehicle to start as it should but as soon as the starter was released, it flicks back to the sensors correct for temperature resistance. So far this has worked well and not given any fault codes. There is a propriety Italian made system that is plug and play for this solution and it costs about £150.

Hi Crasher
I have the same problem, do you remember what size resistor you used? thanks

[Crasher]

If you want to fool the ECU into thinking the engine is at around 20°c, something around 3kΩ