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

[Ben Swann]

SJ,

The CIS-EIII injector connections are different than the CIS-E and the test adaptors are not Banjo fittings..  They are compression fittings.  Fine metric thread on test port as well as the injector fitting where the test lines will go.

I was not able to readily adapt my test guage set to CIS-EIII although it could be used on the other CIS systems.  I don't know if the JCW kit has what he would need either - I speculate based on what I encountered when pressure testing CIS-EIII is that two(2) sets of adaptors would be required in order to have the right combination of adaptors.  Also, don't know if the less espensive JCW kit (around $55)that suposedly does CIS has the proper compression fittings, but I suspect the more expensive (around $300) one does.

Otherwise, great information.

Ben

[Date: Tue, 03 Feb 2004 16:59:16 -0500
From: SJ <syljay at optonline.net>
Subject: Re: SJ Audi 100 Won't Start (Vacuum Leak?)
To: Marc Boucher <mboucher70 at hotmail.com>
Cc: quattro at audifans.com

<snip>
The main injectors will spray only when system pressure is higher than
injector opening pressure.
This test you fail.

*** We don't know that as Marc tested only by removing the line from the top of the fuel distributor - more likely a blockage.

I would suspect a problem with system pressure.

Specs
System Pressure = 88.5 - 94 PSI
Injector opening Pressure = 62 - 67 PSI

If your system pressure is below 62 PSI, the cold start valve will work, but
the main injectors will not work.

Two things determine System Pressure;
1. Fuel pump
2. Fuel pressure regulator.

- - - - - - - - - - - - - - -
Pressure testing.
If you had a pressure tester, it would be easy to isolate the problem. The
gauge itself is simple. The guage is connected to two places at the same
time. There is a reason for this.

The adapter hoses are not so simple. You need banjo fittings. A male banjo
and banjo bolt to fit the lower chamber Test Port on the fuel distributor. A
female banjo fitting is required for the CSV injector line. Also you need a
shut off valve on the line going to the CSV.

With the valve open, the guage will read System Pressure (88.5 - 94 PSI) . .
recall that the CSV valve operates on System Pressure.

With the valve closed(System Pressure shut off), the guage reads the lower
chamber pressure. This pressure is determined by the Differential Pressure
Regulator.
With a cold engine, or a 15K resistor attached to the temperature sensor
connector(simulate a cold engine), the lower chamber pressure should be 17
to 21 PSI lower than system pressure.

If you disconnect the DPR connector( limp home mode), the Lower chamber
pressure will be 4.3 to 7.3 PSI lower than System Pressure.

Because these low readings are within system pressure variations, the
pressure gauge is connected to the two pressure sources so you can flip back
and forth and determine the correct PSI values.

In conclusion, to get your "no spray" of injector symptom:
1. Fuel pump not producing enough pressure to open injectors or,
2. Fuel pressure regulator defective and not providing the required system
pressure or,
3. Internal blockage in the fuel regulator, or
5. Blocked Differential Pressure Regulator. If you get no fuel flow thru the
DPR, the lower chamber pressure is very low .. . that shuts off fuel flow to
the injectors. This actually happens when you decelerate.

Out of the 5 possibilities, and assuming you dont have the fuel pressure
guage, I would guess at 1 and 5. #1 is the cheapest and easiest to test for
fuel flow. #5 is relatively easy to take apart to check for clogging.

SJ

<snip>
> I unplugged the lead to the potentiometer during cranking. . . . <snip>. .
...but it
> could also be a worn potentiometer?
>
> Marc]