Audi a3 1.9tdi warm start issue.

as the post title says - have a problem with warm starting (after using the car for more than say 10 minutes, turning off engine and needing to start again soon after). if I try to start it warm it soon after the engine turns over but "thumps". it may start or may cut out. after it cools down (say 15 mins) it's fine.


battery voltage is fine
no fault codes reading through one of these obd2 readers
http://www.shopmadeinchina.com/product-image/U480-1-5-LCD-Universal-CAN-BUS-OBD2-Car-Diagnostic_12909054.shtml
starts fine when cold
brought it to a garage who said that the water pump should be changed but offer no explanation of how this affects things. (could not find any reference to this online).

any ideas from anyone with experience of this?

shietpilot

What engine code is it? Some TDIs have this issue and the only fix is a remap. Basically there is an Rpm range at operating engine temperature where no fuel is injected. If the starter is spinning the engine at that RPM it won't start. Remap to inject fuel at this range fixes things.

shietpilot

shietpilot wrote: »

What engine code is it? Some TDIs have this issue and the only fix is a remap. Basically there is an Rpm range at operating engine temperature where no fuel is injected. If the starter is spinning the engine at that RPM it won't start. Remap to inject fuel at this range fixes things.

it's BKC.

get the logic about a remap but would this not be a sensor issue that's causing that and the sensor could be replaced?

shietpilot

Yeah it's a common problem particularly with the BKC. The sensor could also be causing it but these are known to not start for the mapping issues.

Some technical details here: https://sites.google.com/site/vagecumap/hot-start-fix

Where abouts are you in the country?

ednwireland

not the camshaft position sensor is it, my octavia needs doing but is showing P3007 fault code

shietpilot

shietpilot wrote: »

Yeah it's a common problem particularly with the BKC. The sensor could also be causing it but these are known to not start for the mapping issues.

Some technical details here: https://sites.google.com/site/vagecumap/hot-start-fix

Where abouts are you in the country?

dublin based

ednwireland

ednwireland wrote: »

not the camshaft position sensor is it, my octavia needs doing but is showing P3007 fault code

is that read from a garage or your own reader?
Is it doable to do that sensor yourself?

ednwireland

ednwireland wrote: »

not the camshaft position sensor is it, my octavia needs doing but is showing P3007 fault code

you getting the hot-start issue also?

ml100

I had the same problem with my 05 vw golf 1.9 tdi, the starter wasn't turning the engine over fast enough for the ecu to trigger the diesel to be injected, new starter solved the problem.

barneygumble99

ml100 wrote: »

I had the same problem with my 05 vw golf 1.9 tdi, the starter wasn't turning the engine over fast enough for the ecu to trigger the diesel to be injected, new starter solved the problem.

If you plug out the temperature sensor I bet it starts first time.

the cam sensor is available pretty cheap
http://www.ebay.co.uk/itm/171753035243?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

seems awkward to fit though.

barneygumble99

barneygumble99 wrote: »

If you plug out the temperature sensor I bet it starts first time.

thanks. you mean the coolant temp sensor?
was thinking of trying that as it's easy enough to do. if that works then the temp sensor needs replacing?

shietpilot

glasso wrote: »

thanks. you mean the coolant temp sensor?
was thinking of trying that as it's easy enough to do. if that works then the temp sensor needs replacing?

If you unplug the coolant temperature sensor the ECU is no longer able to check what the coolant temperature is so it reverts to a basic map which actually injects fuel so it's able to start.

Not a ideal way to run the car though!

shietpilot

shietpilot wrote: »

If you unplug the coolant temperature sensor the ECU is no longer able to check what the coolant temperature is so it reverts to a basic map which actually injects fuel so it's able to start.

Not a ideal way to run the car though!

I get you - so it doesn't mean that the coolant sensor is the problem in this case?

from what i've read on the net it often seem to be the cam sensor that is the issue here (or damage to the wires).

a while ago I got the dual mass flywheel and the clutch replaced - the issues with warm starting appeared soon after. now thinking that it may not be a coincidence - maybe the mechanic didn't attach something correctly or damaged something during the job - could that be a possibility?

shietpilot

glasso wrote: »

I get you - so it doesn't mean that the coolant sensor is the problem in this case?

from what i've read on the net it often seem to be the cam sensor that is the issue here (or damage to the wires).

a while ago I got the dual mass flywheel and the clutch replaced - the issues with warm starting appeared soon after. now thinking that it may not be a coincidence - maybe the mechanic didn't attach something correctly or damaged something during the job - could that be a possibility?

It depends. You need to connect it to a diagnostics kit and to look at live data and see what the sensor is showing.

It could be:
- Some sensor reading an odd value: coolant temperature sensor, camshaft position sensor
- The starter cranking too slowly: slow starter, bad battery

But the sensor should throw a check engine light if it's bad. The remap (not even touching power and just making sure fuel is injected at lower RPM) would probably be the best fix unless you're getting clear indication of something else being the problem. The BKCs have this problem.

As part of removing a gearbox for clutch/flywheel it involves removing the starter. I don't see how it would do any harm unless they damaged your starter and/or replaced it with a crappy one which doesn't spin fast enough.

ml100

ml100 wrote: »

I had the same problem with my 05 vw golf 1.9 tdi, the starter wasn't turning the engine over fast enough for the ecu to trigger the diesel to be injected, new starter solved the problem.

I lived with it for about a year, then when I had to get the clutch and flywheel done I got the starter replaced as they had to remove the old one to replace the clutch so the vw dealer didn't charge any labour to swap the starter for a new one.

ednwireland

glasso wrote: »

is that read from a garage or your own reader?
Is it doable to do that sensor yourself?

glasso wrote: »

you getting the hot-start issue also?

garage read it
used to start on half a turn now takes 2 or 3 when warm fairly minor nuisance really.

ednwireland

Sorry for dragging up an old thread but had my car in the dealers and the cam position sensor was ok but they tracked the faultimate to broken wires down by the gearbox. Sorted it out now starts like dream without that annoying thump.

just dragging this as got it sorted.
the issue after research is that around 90k miles or so the injectors may develop a fault on fuel injection that causes an issue on warm start. car will still work fine outside this. replacing the injectors is well over 1k.
a remap might fix but but the other option is to put in a relay that tells the ecu (through intercepting the coolant sensor signal) that the engine is cold so it sends in the same mixture as cold and car will start fine.
this is only done on ignition so doesn't effect the operating for any other time.
I got this and put it in. it plugs in inbetween the coolant sensor. another wire goes to the nearby 12v ignition wire on the starter motor which allows it to only work on ignition.
http://www.ebay.co.uk/itm/2-0-TDI-Wiring-kit-for-warm-engine-start-problem-elimination-for-2-pin-sensor-/132308070004?hash=item1ece2cee74:g:hFgAAOSw8gVX-ihF

Any garage I went do didn't have any idea what the issue was. most suggested putting in a new starter motor.