Date: Fri, 24 Sep 1999 19:48:53 -0400
Reply-To: John <johnpatt@WARWICK.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John <johnpatt@WARWICK.NET>
Subject: Digijet troubleshooting - (very long & technical)
Content-Type: text/plain; charset=iso-8859-1
Osterwald, Ray wrote:
>
> Hello to everyone,
> I’ve been fighting a problem with my ’84 water-cooled 1.9 (156,000 miles) for about 6 months now.
Hi Ray,
I'm not an expert on Vanagon Digijet systems but I think the source of
your problem is likely the source of many Digifant complaints as well.
While your VW technician has surely tried and you have paid $$$, there
is a serious absence of TEST results. It's one thing to install parts &
try fixes for other engine management systems but it is simplier to look
at the information that the Digijet control module (DCM) uses to decide
how much fuel to inject into the engine under the prevailing conditions.
In the case of the Digijet system, its important to recognize what the
DCM really is. Its a glorified, goddamn voltmeter that decides ONE thing
- how long to power the injectors open by grounding the injectors
negative terminal ! If the DCM can look at specific voltages values and
decide rich or lean, we with the help of a DVOM, can look at those same
values and find the information that is causing your new DCM to inject
too much fuel. Selling this Vanagon for this complaint after all the
money you have invested would be a real tragedy ! The fact that the
vehicle is operated at high altitude means that this is probably not a
large problem. At high altitudes a small injector opening error can
cause your complaint. However the fact that the primary symptom
completely vanishes after a hot restart certainly "thickens the stew" !
Please look at these questions and ask yourself if these test values
have been checked and recorded somewhere. If not, why were the
associated components replaced ? Each one of these input values when
wrong can lead to the DCM injecting the incorrect amount of fuel.
1) What is the normal DCM power supply voltage and what is the voltage
when the symptom is present ?
2) What is the normal fuel line pressure and what is the pressure when
the symptom is present ?
2) What is the air flow meter normal load signal (say at idle) to the
DCM and what is it when the symptom is present ?
3) What is the inlet air/coolant temp sensor full hot signal to the DCM
and what is it when the symptom is present ?
4) What is the cranking enrichment(KL50) signal to the DCM when running
normally and what is it when the symptom is present ?
5) What is the VOLTAGE DROP VALUE (VDV) of all DCM ground circuits (B-)
normally and what is the B- VDV when the symptom is present ?
6)What is the O2 sensor signal voltage normally and what is it when the
symptom is present ?
If these tests seem really basic & repetitive, they are. These questions
simply look at the same voltage values that drive the DCM to open the
injectors. Be a detective and look for the same information (while
troubleshooting) that the DCM uses to compute injector opening time and
you'll find the reason for the extra fuel injection enrichment.
I could have included a lot additional basics, test values and pin
numbers but this message is too busy & too long already. See the Bentley
manual, that's where I get my information !
Good luck, JP