What problem can be overcome by advancing the timing?
Background: Car is a 1988 UK Audi 100 with 2.0 5-cyl RT engine. It is
extremely difficult to start. If I can start it, then it will run ok for
about 10-15 mins then cut out. Difficult to restart if turned off.
I have swapped the warm-up valve, ISV & fuel distributor for known good
ones but no change. Cold start valve ok, idle switch ok, no vacuum leaks
found. Plenty of fuel getting to the fuel distributor. Hall sensor ok -
anyway I always get a spark.
Recently I played around with different ignition timing settings. 18°
BTDC is the standard figure but I'm using regular unleaded for which I
believe the timing should be 8° BTDC. However, the best setting I found
was about 30° BTDC! With this it starts on the 2nd crank instead of
about the 30th. Cam timing seems in order and all my TDC marks line up together.
I've spent ages on this so any explanations of what's happening are most welcome.