Audi 100 Won't Start (Vacuum Leak?)

[David]

I too encountered an no start condition a while back. My NG is essentially the same as your engine. My cr refused to start when I accidently broke the plastic elbow that has  a small branch at the back that goes to a small opening in the engine. It is actually a plastic elbow with one little branch that goes down. The opening on the small branch is tiny. But when broken, it causes BIG no start conditions. Might want to check it out, mine was VERY brittle. The part is still available from any VW or Audi dealer for well under $5...

Dave
87.5 CGT
SE Virginia
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From: "Marc Boucher" <mboucher70 at hotmail.com>
Date: 2004/01/27 Tue AM 02:26:01 EST
To: "SJ" <syljay at optonline.net>,  <quattro at audifans.com>
Subject: Re: Audi 100 Won't Start (Vacuum Leak?)

I performed the vacuum test as described.  Getting a good seal on the air
bonnet was a challenge but once I tried latex gloves for sealing it, the
problem was solved.

The system was 'essentially' sealed.  By this I mean that if I created
either a positive or negative pressure situation (small pressure, using lung
power) and sealed with my finger, it would take at least a five seconds for
that pressure difference to dissipate.

I investigated and found at least one source of this small leak:  The hose
that leads from the ISV to the air bonnet actually has a small branch at the
back that goes to a small opening in the engine.  From what I can tell from
various diagrams, this opening leads to the injectors.  The hose itself has
no leaks.

Could such a leak be the cause of my non-starting condition (I'm doubtful).
Remember that this car went from 'never failed to start', to 'impossible to
start and drive'  overnight.

I just remembered that many things get energized once the ignition key is
turned (I think including a vacuum reservoir to open close vents/climate
controls?) So I'd best repeat this test tomorrow with the ignition on.



Thanks,

Marc


----- Original Message ----- 
From: "SJ" <syljay at optonline.net>
To: "Marc Boucher" <mboucher70 at hotmail.com>
Sent: Monday, January 26, 2004 9:32 PM
Subject: Re: Audi 100 Won't Start
**** I havent done this yet, because its too damn cold . .. but to find a
vacuum leak I would take off the air bonnet at the fuel distributor. Make a
wooden or metal or plastic plate to position on top of the fuel distributor.
Cover that with a plastic sheet. Install the air bonnet over the plastic
sheet.
Now you have the intake sealed. The other end is sealed by the engine
valves. You now have a completely sealed system.
Use one of the unused ports at the bonnet to supply air to this sealed
system . . .and look for leaks. You can just blow into it using lung power.
If it doesnt hold air, you have a leak. A steady supply of air at a low
pressure . . .say 3 lbs would be ideal for locating the leak. Just use a
hose pressed to ear to look around for the sound hissing air.

Some hoses you can block off . . .like PVC hose. But, the crackcase system
is also sealed.

SJ
85 Dodge PU, D-250, 318, auto
85 Audi 4k - - sold but still on the road
88 Audi 5kq
90 Audi 100q



> Today I pulled both control units.  Their plugs were pristine as were the
> units themselves (wrapped in plastic).  No sign of moisture or rust.  The
> wiring I'm not so sure of.
**** Good idea to use electrical contact cleaner and plug/unplug several
times to clean contacts.
>
> Thanks again,
>
> Marc


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Dave
2002 Jetta 1.8T (hers)
1993 RX-7 R1 (weekend play toy, soon to be for sale)
1987 CGT Special Build 2.3
in Virginia Beach, VA.