random won't start
 

99 a4 1.8T. at random wont start. i feel its electronic not a fuel issue. i replaced the ignition amplifier. no change. regardless of temperature outside or engine temperature, length of trip etc...it throws no code. any one oelse been thru this ? thanks

does it crank but not turn over?? i had a problem with my starts too but it was starting when the car sat for more than 2 hours at a time. i changed all four coil-on-plugs and it did the trick. when you turn your key to the on position listen for the fuel pump to kick in you should hear a wizzing noise if you dont hear it you pump may not be supplying fuel. other than that your battery might be bad at which point you get a whole lot more problems. check your terminals to see if they are tight. i would run fuel system cleaner in there jsut to make sure you dont have any clogged injectors or any other kinda build up in your system lowe quality gas does make yor car start alot harder also. this is a link to my other thread i had hard starting problems
https://www.audiforums.com/forum/sho...d.php?t=111191

Do a Seafoam treatment.

fuel pump kicks in. fuel filter changed. i'm pretty certain it's ignition related. i've had ignition coil issues in the past but i've never had one or two coils be bad and cause a no start issue. it's usually a rough start/idle when a coils bad. i've changed the ignition amplifier and the issue is still present but randomly. I'm trying to locate an ecu to borrow and try. oh ya the battery checks out. thanks for the input/reply.

you still having troubles bro? if you are check out this thread it might be your problem like it did mine. replacing the coil packs and fuel filter and plugs and fuel pump relay on mine and its still wont start so i looked and foudn the engine speed sensor ore impulse sender was bad. here is the thread its a 7 pager but very useful info on the ignition system. the actual DIY is on page 6 or 7 so try it the part number i had was 078906433a but it could differ with your make model year. i have 2002 audi a4 quatto 1.8t try this though its easy
to test the sender there is three prongs coming out of the harness and you just check it with a ohm meter on pins 1 and 3 so not the middle one. the regular spec is 730-1000ohms if you are getting mroe or less than that its bad sender unit.

https://www.audiforums.com/forum/sho...impulse+sender