Audi A2 - Long Crank when Warm

[Nognar]

Ladies and Gents,

I know its an A8 forum but I am not getting much from the A2 forums on this one and its causing me a real challenge on working out what it going on with the little runabout.

So I thought I would ask the collective for your thoughts, as you will see I have done a lot already to try and work this one out!

Car is a 2001 1.4 Petrol AUA, 114,000 miles and drives perfectly, its a 1.4 16v lump as seen in the Polo & Fabia etc.

Once the car is started there are zero problems, it drives beautifully.

The car sometimes starts perfectly but is normally when its cold outside or its been left overnight. When warm outside or warm as been driven and left for 30 minutes or so it takes a very long crank to get it to start. If when started I take the key out and try to start it immediately it starts perfectly again.

So to cover off a few questions and things I have already done in my rather large quest to resolve this:

1) The car when started drives perfectly, without fault and MPG is good
2) There are no lights on the dash and no error codes in VAGCOM
3) According to VAGCOM everything is good and working, sensors giving good readings and measuring blocks look good, there are no fault codes
4) Earth points checked and cleaned, under the bonnet by the lights and the two A pillars
5) Car has been fully serviced including new spark plugs, oil and filter
6) New Bosch HT Leads fitted
7) New NGK Ignition Coil fitted
8) New Fuel pump fitted (VDO)
9) New Fuel filter fitted (Mann)
10) New coolant temp sensor fitted (Febi)
11) New MAP sensor fitted
12) New camshaft position sensor fitted
13) TPS checked and adapted
14) Throttle body checked, cleaned and adapted, plus replaced also to check with another unit
15) New Injectors fitted
16) One way valve fitted to fuel pipe leading into the fuel rail to see if there was some form of pressure drop at the rail itself
17) No fuel leaks that I can see from the tank, pipes or engine bay
18) Fuel pipes look all good, no fuel smells, leaks or drips
19) Injector cleaner and fuel cleaner run through the system
20) New Varta Silver battery installed
21) New PCV Oil Separator fitted
22) Pipes and breathing looks good on the car, no obvious vacuum leaks
23) New Oil pressure sensor fitted
24) Spare Key tried in case this was an immobiliser problem
25) New Fuel Pump Relay (612) fitted
26) New front Lamda sensor fitted
27) Battery terminals checked, all good and clean etc
28) Another fuel pump fitted to triple check
29) Another coolant Temp sensor fitted to triple check (Meyle)
30) Full tank, empty tank of petrol makes no difference to the problem
31) Crank position sensor replaced and tachometer does move in start up *EDIT

With all of the above done, whilst making the car run even better made no difference to the starting problem!

If I run the fuel pump for ages before starting with the key in position 2 it does not have any impact on the starting problem. Its been like my little challenge to try and fix but I am running out of ideas here, its like perhaps vapour lock or it needs an Exorcism!

[MikkiJayne]

You don't appear to have changed the crank sensor? Thats a fairly typical failure mode for it, and it doesn't show a code as the ecu doesn't know the engine is turning.

Does the tacho move during a failure to start event? It should be showing ~200-300 rpm, enough to tweak the needle.

[Nognar]

Sorry I missed that off the list!

Crank position sensor changed also and the tachometer does move when cranking.

[pete-p]

Could one of the sensors (coolant or crank) be faulty even though you replaced them? Perhaps the pins or wiring are the issue?

[HPsauce]

The symptoms are very typical of a faulty CTS I must say, having had a few on different cars.
Did you buy a genuine VAG one when you replaced it (I've been bitten by cheap eBay clones too!)?
One relevant test is, when hot and not starting, quickly floor the throttle. If it then fires up more easily it's another pointer to the CTS.

Remember the CTS has two circuits in it, one for the dash the other for the ECUs, so a plausible temperature gauge on the dash proves almost nothing.
Unless the A2 uses a very different system......

[Nognar]

CTS is a 4 wire unit and I have tried a Febi and Meyle one in there to try and solve this.

As agreed it’s what my thinking was one of the likely areas, it’s worth noting that it’s the same as a D2 one (059919501A).

I wonder if I have an old Audi one still in the spares bucket…..

[HPsauce]

Originally Posted by Nognar

I wonder if I have an old Audi one still in the spares bucket…..

In the end with mine I just went to the local VW dealer and bought one over the counter from the spares dept. With a clip and o-ring as they are separate items.

[Nognar]

I have found an old good A8 Coolant Temp Sensor in the spares box so just fitted that.

Lets see.....

[Nognar]

Nope

Has not solved the problem

[ainarssems]

Seems like you covered most bases. I have no personal experience with petrol not starting when warm. 1st thing that came to my mind it runs too rich or flooded when when warm because some injectors might be leaking but you already changed them. Next would be crankshaft sensor but that has been changed as well. Now I know some Vag diesels experience this problem because there are minimum rpm to start injection when cranking and the minimum is different at different temps with higher temps requiring more rpm before injection starts. When the starter or battery or both get aged at high temps sometimes they don't reach minimum rpm to start injection. The solution is usually either changing starter or remapping ECU to allow injection to start at lower rpm. I don't know if petrol engines have similar limits. I would start with test light or oscilloscope tapping into injector and coil wires to see if they are firing followed by crankshaft sensor.