re. i87 5kt intermittent no start

[Ben Swann]

Dave,

 

Vac hose is standard dealer stuff – expensive and I use every bit of it.  You’ll easily
go through at least 10’ of it for your car.  

 

You need to have no air leaks because when the engine is turning over, air is drawn in
through the throttle body + ISV which is all routed through the intake tract, including
turbo and intercooler.  This air draw lifts the sensor plate – if you have a leak, the
plate will not lift properly and fuel will not get to the injectors.  Cold start
injector may provide enough fuel to compensate sometimes.  Once started, the RPM is
enough to draw air faster than a small leak and lean condition will be compensated for
to a degree.  

 

ISV regulation is needed when starting since it allows a little extra air to pass.  The
engine management will cause ISV to open fully as needed without throttle being open.
Timing is dealt with when Idle switch closed, so you really shouldn’t put foot down –
although sometimes this works when compensating for a leak, by making a larger air draw,
but AFAIK the timing will not be proper for turning over the engine when the throttle
switch is open, so putting foot on pedal is not supposed to be the trick to starting the
engine.  Neither is pumping the gas pedal or holding all the way down to clear flooded
condition – this is how carburators deal with it, not fuel injection.

 

Injectors – as the get old, they tend to weep and bleed pressure down.  When this
happens there is no residual pressure in the lines so delay in starting.  Also if you
got a lot of crap in or old gas or water in the gas went through the CIS, you may have
gummed or clogged some things – namely the warmup regulator and/or metering head.  A
simple sanity check is to run fuel pump (insert fuse into relay with key on to initiate
output test).  Then try to raise the airffow plate manually.  I usually use the 3mm CIS
adjustment tool (long allen wrench) and lift the plate with just enough force to hold
the screw but not turn it.  Or you can remove the air filter housing and reach under by
hand.  The plate should lift easily with no binding and you should immediately hear the
squeal of fuel being injected.  Don’t overdo it or you will flood the engine.

 

We can take a look at the car at Carlisle – I hope to be there in the green “Inga” Ur
Quattro – no longer CIS.

 

Cheers!

 

Ben

 

  _____  

From: Dave Yentema [mailto:yentemad at rider.edu] 
Sent: Wednesday, May 14, 2008 10:10 AM
To: Ben Swann
Cc: quattro at audifans.com
Subject: Re: re. i87 5kt intermittent no start

 

Ben, thanks.

 

I now have the right screw for the car, and i know that for a fact. The timing i'm not
so sure on, it runs like a champ once its running, just hard starting. I need to pull
the cover and take a look at it. I'm no longer throwing any codes for anything so i'd
assume it was ok. 

 

I tested the switch with a DVM, and i will double check it again today. Knowing my luck
and how the audi gods love to play with me, i'll go out there and the car will run
perfectly

 

You wouldn't happen to have any of the vaccum lines in good condition to bring to
carlisle would ya?

 

-Dave