SJ Audi 100 Won't Start (Vacuum Leak?)

[Marc Boucher]

Here are the results of today's testing (pulls out his log book :-)

TESTING OF THERMOTIME SWITCH:
Both pins measured about 3.5k Ohms from ground to the pin.  At about 50F
this is quite close to your results.

TESTING OF IDLE and FULL THROTTLE SWITCHES:
Confirmed...on idle the switch is engaged (zero ohms) between pin 1 and 2.
On full throttle we get zero ohms between pin 2 and pin 3.  (I know its not
technically zero ohms...guess that's called 'closed circuit' ?)

TESTING TO ELIMINATE FUEL PUMP RELAY AS CAUSE:
This had been done yesterday and results reported.  Key point is that on
removal of the relay and shunting, the fuel pump can be heard to operate,
and is measured to draw about six Amps.  Starting of car while using the
shunt produces a result that is NO different than using relay.  Conclusion:
Relay is likely not the problem.

TESTING OF FUEL PUMP OUTPUT:
The fuel pump was disconnected at the entry to the filter (filter is new-was
changed as a first step in trying to solve this problem) and carefully
directed into a container in which I could measure flow.  Fuel pump was
energized for about 2-3 seconds...during this time it pumped about 60ml (2
fluid ounces).  Note that I don't have the equipment to accurately and
safely test flow, or to test it under pressure.  But this test gives me some
confidence that its pumping and more than likely the pump is not the
problem.

TESTING OF CURRENT FLOW THROUGH DIFFERENTIAL PRESSURE REGULATOR:
Today I was not successful in getting the car started.  Thus the current
flow would be about 100mA once the ignition was engaged, remain at that
during cranking, and once the key was released (released because it seemed
like it was starting) the current essentially followed the rpm...i.e.
descended from 100mA to zero just as the rpm descended from 1000 to zero.
Time between releasing key and zero rpm was almost always under 1.5 seconds.

TESTING OF POTENTIOMETER DURING STARTUP:
Previously I'd tested the potentiometer resistance with the bonnet open.
I'd found that The resistance between the bottom and the middle contact is
about 2 kOhms at rest and rises to a max of about 13kOhms near full open
falling slightly to 11kOhms at full open.  Today I decided to measure this
resistance during an attempted start just to ensure that the plunger is
actually moving.  The resistance moved from about 2 kOhms up to about 4 or 5
kOhms. when it appeared that the engine was about to start and then as it
sputtered the resistance fell back to 2kOhms.

TESTING THE EFFECT OF UNPLUGGING OXYGEN SENSOR:
O2 sensor disconnected (heater and sensor plugs).  Result...no change in any
observed behavior.

Two of your suggestions...the inline spark plug tester and the starter fluid
will have to wait until I can get a ride to a car parts store.  The spark's
been verified but you're right, it could be intermittent.  I'll try to get
both as soon as practical...note however, with regard to the starter fluid,
its really too cold to barbecue up here right now :-)

Marc



----- Original Message ----- 
From: "SJ" <syljay at optonline.net>
To: "Marc Boucher" <mboucher70 at hotmail.com>
Sent: Wednesday, January 28, 2004 11:38 AM
Subject: Re: SJ Audi 100 Won't Start (Vacuum Leak?)


Theoretically, the car should run without the fuel injection ECU. The system
will run in a mechanical mode.
Basically, all the ECU does is vary the Diff Press Reg current to fine tune
it for emissions.
The other ECU outputs are minor, ISV, vapor canister, cold start valve, etc.
Many of the inputs to the ECU can be "faked" . . ie, resistor in place of
temp sensor, jumper for idle switch, etc

Are you keeping a log of your tests?

Things that you arent doing and should be doing.
1. Get that $7 in line spark plug tester . .and leave it on. Just in case
you have an intermittant ignition problem.

2. Hook up the ammeter for the Diff Press Reg. I use a cheap analog meter .
 radio shack. You can calibrate the analog against the DMM. Always monitor
this current . . . you should have a list of current values and conditions.
I sent you an email with these values.
Both my cars have insulated male and female spade lugs crimped on one of the
regulator wires. And I made up lug type test leads to interconnect to the
wiring and my meter. Now its very simple to hook up a meter.

3. Get starter fluid and rig up rubber hose so you can inject the fluid. Its
a lot easier to troubleshoot if you can get the engine to run. The starter
fluid will bypass cold start valve and lean mix from pressure regulator.