Very intermittent Start/stall on TDI150

sockpuppet

Active Member
Apr 30, 2007
837
4
When I start the car it initially sits at 500 rpm for about a second and will then normally rise to 900 rpm and run fine, it always used to go straight to 900 rpm every time up until a few months back. It's almost as if the timing is out for a second and then corrects itself.

Over the last few months out of 300-400 starts it has started at 500 rpm and then stalled about 8 times (getting more frequent), it has happened more often when the car is warm but also a couple of times from cold.

I have code read with vag-com and there are no error codes, the battery is about 2 years old and the starter motor is about 18 months old, battery reads 13.4 when off and 14.4 when running (through the torque app).

Anyone got any ideas where to start on this and what to check on vag-com?
 

Dan FR

Meth addict. Stage 2+ Yo!
Nov 14, 2013
1,795
8
Caerdydd
Battery won't read 13.4 volts unless you have just switched the car off. On a cold start it will be in the 12-12.6v region

Last time I saw symptoms like this it was down to an injector(s) and the issue went away when they were swapped out with another set. It appeared that they didn't fire correctly on initial start-up but after a few seconds ran fine.....

Check the injector balance along with the response time (can't remember the blocks, maybe 14 and 21 or 22?). May or may not show anything useful unless you check it on start-up
 

sockpuppet

Active Member
Apr 30, 2007
837
4
The 13.4volts was when I had just turned the car off and through torque, not a multimeter.

It's quite possible it could be the injectors as they are still original, 10 years old and 215000 miles.

I will look on ross-tech site and see what the blocks I need to look at.
 

sockpuppet

Active Member
Apr 30, 2007
837
4
First thing I have tried is wynns injector cleaner, I dumped a bottle of that in on friday and the car has started easily every time so far. It is a very intermittent problem so it could just be coincidence.

If the injector cleaner doesn't help then the fuel filter is the next thing on my list as it's cheap and easy to change.
 

sockpuppet

Active Member
Apr 30, 2007
837
4
I think my problem was using supermarket fuel. I am on my second tank of shell vpower nitro+ with millers ecomax and the car has started without any hesitation. I plan to run it on the nitro+ and millers for the next 5000 miles which should clean the fuel system, then I will look for a cheaper fuel that is better quality than the supermarket and keep using the millers.
 

sockpuppet

Active Member
Apr 30, 2007
837
4
I used it once before and didn't notice any difference at the time, it's supposed to have detergents and boost the cetane level. It's a cheapish option costing just over £1 per tank of fuel. If you try it, it's worth buying a container to keep the bottle in as the stuff stinks once the bottle is opened.
I got a litre of the stuff which should do me for 10000 miles.
 

sockpuppet

Active Member
Apr 30, 2007
837
4
TDI Hot start stall. Workaround Fix.

Since I first posted this the problem got worse to the point where it would take 8+ attempts to start the car when it was hot (Instantly started when cold) where the engine would fire up and idle around 600 rpm for a second and then die.

I looked on all the forums I could find for info and I found three possible reasons for this, the first 2 I ruled out (CTS sensor fault) and (Sluggish starter motor) so that left the fuel pressure valve. There is supposed to be a fuel pressure valve to keep fuel pressure at a certain level when the car is turned off, but my guess is that the valve is releasing the pressure and when the car is hot there is no initial injection of fuel/fuel pump priming which happens when the car is cold, so there is not enough fuel to keep the car running.
As I couldn't get any info on where the pressure valve is located and didn't want to pay £200+ for a fuel pump and all the hassle of fitting it, I fitted this device instead. http://www.ebay.co.uk/itm/Wiring-ki...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

It basically disconnects the CTS when the starter motor is turned over meaning there is no signal to the ECU which makes the car assume it is cold so it injects some fuel. Once the car is running the relay connects the CTS so the car runs as it should.
It has completely fixed the hot start on my car.
 

Dan FR

Meth addict. Stage 2+ Yo!
Nov 14, 2013
1,795
8
Caerdydd
You have a slow starter motor that isn't turning fast enough when warm - if you have replaced the battery and starter then chances are its the wiring between them

Could have patched it out in your map for you if you have the means to read it from the ECU - 2 minute job

Don't think I've ever seen a hot start issue on a PD150 though - usually only on the Mk5 Chassis and I would have never guessed it based on your original description.
 

sockpuppet

Active Member
Apr 30, 2007
837
4
I didn't think it was hot start only when I wrote the original description as I had the revs hunting at 600 and then stalling once from a cold start. It got progressively worse to the point where it was happening every time when hot. It is possible that it could be a slow starter motor when hot, I couldn't find a way of checking the starter motor speed, I tried block 01 in vagcom and it showed around 770 rpm every time before stalling so I'm guessing that must be the engine speed rather than starter motor speed. Anyway the device starts the car whether it is fuel pressure or starter motor so I am happy with it.