Re: Ur-Q Hot Start Problem

[paul.heneghan@bbc.co.uk (Paul Heneghan)]

From: pacdev@csn.net

>When cold (i.e. overnight) it starts great. As soon as engine temp gets 
above
>100 C it will not restart.

>Then back to square one. I've plumbed the Bentley and the
>Ur-Q manual and have yet to find a reasonable explanation of a) Hot start 
relay
>system  b)Thermo time switch, c) temp sender.

Hot start problems are usually caused by vapourisation of fuel in fuel lines 
due to excessive heat, or low standby pressure in FI system.
Reasons could be:
a) excessive under-bonnet heat
     try flushing/replacing radiator
     changing oil more often
     changing type of oil
     check ignition timing and mixture
     running fan when engine turned off and engine compartment still hot
     check injector fan OK (only on some models)
     install injector fan
b) FI pressure collapsing when engine turned off.
     pressure accumulator should prevent this - check PA
     injectors could be leaking - they should stay closed when ignition is 
off
     cold start injector could be leaking
     check valve on outout of fuel pump might be leaking
     Get FI expert to check pressure on shut down
c) Some models pulse the cold start injector which helps a LOT during hot 
starting
     Wire a switch to allow CSI to be pulsed manually by driver
     Buy kit (for Porsche 924, VW GTi etc) which has a pulsed relay
     This kit was available in the UK a few years ago for about GBP30

It should be fairly easy to wire a switch to the cold start relay just to 
confirm if this technique will work or not - don't flood the engine!

Thermotime switch activates the cold start injector for a few seconds to 
give the extra fuel necessary for successful cold starting.  If the 
temperature is 0C, you might get 5s.  If the temperature is 15C you might 
get 1s.  Check Bentley for exact times for your model.

Paul
paul.heneghan@bbc.co.uk
1984 Audi 80 quattro
1989 Audi 100 Avant