Car won't start when hot. Help

[thebluewhale]

This started yesterday.

I left work and drove the 10 miles to pick up my lad from school. The car was OK, no problems at all. Tried to start the car outside the school and all I'm getting is the engine turning over and not catching.

Bollox, me thinks. 'C'mon we're walking' I says to howls of terror as I make my lad walk all of 300 yards.

I get home and call the AA who say they'll be there in half an hour. I get back to the car and try it again. Fecking thing starts first time. Cancel the AA very quickly. I took the car out later that night and it was OK.

Same thing happened today at my second home the Shell Garage. I stopped off on my way home, tanks up and tries to start the car. The same as yesterday happened - turning over but not catching.

I sat there for 10 minutes trying not to look like a tit while the fecker just turned over and over and over. Just about to call the AA again and it bursts into life. Arrrrrrrrrrrrrrgh.

So,

Has anybody had this problem? What was it and how did you fix it.

It may be heat related and I've had some guesses at fuel pump relay or crank sensor maybe?

I'm taking my VCDS lead with me from now on as no fault was found on the scan.
Will a fault show if I plug in VCDS when it happens and what am I looking for? Measuring blocks or something?

I'm a Vagcom novice so I'll need VCDS for idiots instructions please.

As always, your help is appreciated

[S8yot]

I had exactly the same symptoms with my D2 S8. Eventually refused point blank to start at the most inconvenient place! It was the crank sensor. Garage did the work as I assumed the sensor would have been in the most inaccessible place as usual. Wasn't too expensive from what I recall.

[47p2]

I would agree that it's the crankshaft position sensor, common for them to go dead when hot and work ok when cold

[thebluewhale]

Thanks guys.

Any idea where it's located and how hard it is to change?

[47p2]

Should be on the bellhousing somewhere, usually around the top half. Sorry i don't know exactly for your engine, but you should be able to see the wiring going to it

[Adrian E]

The connector in the engine bay should be a 3 pin on the bulkhead in front of the central filter housing - I tried attaching them but they're in xps format as don't have pdf writer on my laptop.....it looks like Elsawin shows LHD so not sure if it swaps sides, but diagram shows it more to the passenger side.

There's a test procedure for confirming if it's knackered as well, which involves measuring resistance across pins 2 and 3 of between 450-1000 ohms (based on 20C ambient and goes up with air temp). Pin one is the squared end of the 3 pin connector.

If that looks OK it then suggests checking for continuity across pins 2 and 1 (earth) and pins 3 and 1. Should be no continuity and if there is then it's new sensor time.

Other than that it suggests a physical check of the wiring to the ECU....

[thebluewhale]

Thanks for the info Adrian.

Has anyone got the part number for the AQH engine so I give TPS a call tomorrow?

Steve

[Adrian E]

If you can read .xps files on your computer, the attached zip file will extract to 2 .xps docs from elsawin

Don't know my way round Etka well enough to be sure of an accurate part number - not even sure I've managed to find a full list of engine sensors to be honest!!

[Architex_mA8tey]

Take a look at the attached - I presume you're after the "hall sensor" that fits around the impulse rotor? part numbers are on the graphic too

[Nollywood]

Yeah, I'd say crank sensor. Easy to replace, I replaced it on my old '98 S8, and on my '03 B6 A4 3,0 quattro tip. On both cars, I accessed the crank sensor via the passenger's side wheel arch.

10mm bolt, or an allen-head one, depending on model. Took about 5 minutes after raising the car slightly.