fuel pump + cold start + hesitation on 86 4kq

[Ti Kan]

Brady Moffatt writes:
> [ 4kq ]
> 1) When I turn the key to ON, I hear nothing. On my VW Golf, the fuel pump =
> would run for a couple of seconds. Not so on the Audi. Is this normal? If I=
>  have a small pressure leak back into the tank or something, I would assume=
>  the pump would build up the pressure again. Which brings me to the cold st=
> art issue....

The fuel pump relay is "supposed to" do that on the Audi 4k series as well,
but I have seen plenty of VWs and Audis whose FP relay either don't do that
at all, or do that only sometimes.

> 2) The first start of the day, now that the temps are dropping into the low=
>  40s at night, is a real fight. It takes at least 10 seconds of cranking to=
>  fire up. I can't bring myself to crank for 10 seconds at once, so this is =
> spread over 2-3 tries. There is the odd stumble, then the engine grudgingly=
>  starts up. I do this with my foot off the gas. If I hold the pedal to the =
> floor part way through, it will backfire lightly then start.No faster thoug=
> h. Once started it runs well. The idle's up slightly, good throttle respons=
> e. Actually better than when it's warmed up, which brings me to the hesitat=
> ion...
> 3)There is a hesitation/light miss/bog from idle when the engine is warm. I=
> f I floor it in neutral very briefly, then I can accelerate away from idle =
> with no bog. When the engine's cold, it doesn't do it.

Sounds like you might have a cold start system malfunction.  First thing
to check is the integrity of all the intake system hoses, vacuum lines,
etc for leaks.  Then, check the cold start valve.  Also check the injectors
for proper spray pattern.  If all that checks out fine, then perhaps some
basic settings need to be adjusted (idle, basic fuel/air mixture, ignition
timing, differential pressure regulator duty cycle, and basic fuel pressures).
If you want to try doing these yourself, be sure you get the Bentley service
manual.

> What I've done about it and plan to do
> -dumped in a can of injector cleaner
> -plan to remove and clean the idle stabilizer valve

These are fine.

> -plan to richen up the idle mixture a bit (CO screw?)

I wouldn't really recommend doing this blind.  Even if it seems to make
the problem go away it would a band-aid fix.  You should only be tweaking
the basic mixture using the Bentley manual's procedure.

-Ti
01 S4 2.7 biturbo quattro
84 5000S 2.1 turbo
80 4000 2.0
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    ///  Ti Kan                Vorsprung durch Technik
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