Investigation further[ Fusebox internals - map/diagram]

[Ben Swann]

OK - I have been poring over wiring and connectivity to figure out why the engine does
not start and run.

Recap for those who are interested:

ABY "S2" engine installed with ABY wiring harness.  All connections for the harness are
to the fusebox per factory.  Ancilleries like instrument cluster - Tach, etc. are left
unconnected.

On Crank, the fuel pump does not run.  Checking obvious suspects starting with Hall
Voltage and operation - that is good and switching.  

Diagnostics attempted both by wiring for VAG-COM and simple LED test hookup do not work.
The LED lights when switch on with ECU but not signaling.  I did verify all wiring is
connected properly -  OBD power +/-, OBD K/L, OBD blink.

I don't want to just plug another ECU in since if wiring is incorrect and full voltage
on wrong pin could concievably be damaging the ECU.  So I checked all harness pins at
connector w/o ECU:  

First testing all 55 pins w/r ground no battery negative connected: Pins 7, 10, 14, 19,
24, 26, 52 showed some connection to ground.

With battery connected: checked for voltages reveal: 12V on harness pin 18 - that is the
unswitched power supply so OK.   What did not make sense is that I saw 3V on pins 3 and
27.  Both these lead back to the Fuel Pump Relay terminal 
That corresponds to ignition on - I think, terminal 86 on the relay.  Some diagrams show
as 46.

Anyway, I'm wondering where that 3 V is coming from.  It is fairly consistant -
something in the car like a voltage regulator or the current that goes through a relay?
Is this normal?  That is if the key is off and voltage checked on the relay terminal 86
[no relay inserted] that voltage is around 3?  Would this cause a current drain or just
voltage present?

Also, I continued to test through all 55 pins again - when ignition switched on, I got
12 V where there was 3V ( pins 3 and 270 and also on pins 
18.  8.75V on  terminal 50 (vehicle speed signal - from tach)?  

Weirdness.

Ben

-----Original Message-----
From: Huw Powell [mailto:audi at humanspeakers.com] 
Sent: Saturday, September 25, 2010 11:58 PM
To: John Cody Forbes
Cc: Ben Swann; quattro at audifans.com; 200q20V mailing list
Subject: Re: Fusebox internals - map/diagram

That tests the ECU and whatever POSs are.

It doesn't actually "check for spark", though.  Bad coil, bad plug, drowned spark, you
wouldn't find them, right?

> Just use a logic probe to back probe the coil connector for checking 
> for spark. If the signal is getting to the coil then the ECU is doing 
> it job as well as the POS's.


--
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/