Date:         Fri, 25 Apr 2003 09:50:05 -0700
Reply-To:     Mark Keller <kelphoto@SHAW.CA>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Mark Keller <kelphoto@SHAW.CA>
Subject:      Diagnosis of Intermittent Power Loss or Misfire
Content-type: text/plain; charset=us-ascii; format=flowed

Steve Gough wrote:

>  What is wierd is that
> the van will often (but not always) run well in open loop, with
> good acceleration and power, both hot and cold.



Steve and listees,

Well I want to send this response to the list as I believe a couple of
important points can be restated for the benefit of us all.

Steve's case of the intermittent misfire has some lessons for us all. As
you can see below the procedure to irradicate the dreaded misfire can
and often does have an electical component.  What we all often overlook
is the condition of the actual wire harness.  I've excerpted some
diagnostic wisdom from an unknown author, so if it's yours thank you
from us all.  The excerpted material is a condesed set of procedures
that should be done without shortcuts to solve a misfire. While I  avoid
getting this nitty gritty on most of the cases I respond to, I feel we
all should read through this and contemplate that I next issue of
misfire, either Our own, or someone on the list, might do well to
examine the wiring harness first.

It is a forgone conclusion that many mechancial dianostic approaches are
designed to be quick and painless, although usually the "test" involves
purchasing some electrical part. This is a murky issue, becasue no one
part is consistantly the bad guy.  I've heard, TEMP II, O2, AFM, ECU all
bandied about, because at one time or another all of these parts have
been reported go bad, fail early, and crack solder joints, or just plain
give up because of marginal engineering.

I'm of the diagnostic opinion that  for testing the engine should be
left in open loop mode, until the problem is resolved, it makes
diagnostics much simpiler, and the Bosch Electronic engine controls were
actually produce in the hundreds of thousand unit without  the O2.  The
engine can flat run better on a given day without the O2.  The O2 has
it's purpose in a well tuned engine, but for the sake of testing, it
should be the first thing to be taken off line. Now on to Steve's issue:

Now then I had not seen this, statement before, that what we are
actually working on is an intermittant issue.  This changes things.  If
you problem comes and goes, then I believe your should do a couple of
things based on unknown to me author who condesed  the Factory  Test
Sheet for intermittent misfire.  I' m not able to key it in just now,
but here are some of  issues: In order of the test sheet.

1. Ignition system, "if you have the Beru spark plug connectors replace
them"

2. Coil -- you should have the "GREEN" Labelled coil Part # 211 905 115d

3. Electrical Harness Check-- Check the connectors in the ECU Plug and
at all the other fuel system components connections. ARe the connectors
in good shape, with a solid crimp on the wires?

4. Are they the union power timer connectors?  Power timer terminal can
be recognized in the following way:  These terminals are basicazlly the
same as teh original excetp that a stainless steel spring is crimped
over the original terminal contact fingers. Thes keeps tension alonf the
contact surface during movement, vibration and high curent draw.

Fuel injection wire harness internal connectioan ( injector power and
ground terminal #94 , G1 and G2 butt type connector inside the
harnesscover can aslso be a problem.

Intermittent missing in lower gears and some at highway speeds. These
three connections are to be soldered. the author states "I have no other
information on the exact location of these buttconnectors other thatn a
photo copy that istoo dark to point out anything and the communique
states see your District Service Manager for approximate locations"
Refer to harness check in the microfiche or the Digifant I and II
ProTRaingi manual pages 40-43, (Yes I know Darrell has these pubs.)

Other than  that, the list also say to double check the Evaporative
system, pg 34 of the pro training manual.

I would add that on all connectors I have done the following.  Dipped
the terminals in a solution of  TARN-X, then a clear water rinse, air
dry or compressed air dry, then coated the terminal with a Product
called "OX-GUARD"  I prefer this product as the label incates that a
dielectic grease base with a conductive grit.  This allow the connectors
to "bite" into the conductor grit.

This service takes all day to do, but I found my van to be more stable
in differnet weather and climate conditions and operations, all which
have an impact on marginal electrical connections.

Sincerely,

Mark Keller
91  Carat