Date:         Sun, 18 Jan 2004 15:22:50 -0500
Reply-To:     "Daniel L. Katz" <katzd54@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         "Daniel L. Katz" <katzd54@YAHOO.COM>
Subject:      Re: 85 wbx 1.9 miss at idle

1.  see

http://www.geocities.com/harald_nancy/intermitt._syndrome.htm

for superior discussion/fix of vanagon intermittent syndrome. much in
archives on topic as well. doubt ECU is at fault, but not impossible.

2. not sure what was on VW's mind concerning digijet factory 5 deg ATDC
initial ignition timing, but list consensus seems to be that 5 deg BTDC is
an improvement. advancing timing results in higher peak combustion
temperatures and more complete fuel burn, and therefore a higher thermal
efficiency - hence increased max torque and horsepower, and more mpg. the
higher combustion temperatures will produce somewhat more NOx, though. on
some cars factory timing seems to be very conservative to avoid any
possibility of ping or knock.

early 70's saw many chevy v-8's, even with modest 8.5:1 compression
ratios, set factory about 6 deg BTDC initial timing, but cars ran better
with timing set roughly 14 deg BTDC, more advanced yet at high altitudes.
best timing method on those cars was to keep advancing initial timing
until they would occasionally give a little ping on hard acceleration or
on hills, then slightly back off timing so engine was on the verge of
pinging; full advance was around 50 deg BTDC (high cruising speed and
light throttle).

if engine is missing and has poor idle, it may be difficult to set timing
accurately. i have had the experience of trying to set initial digijet
timing with rough idle, but discover later on, with engine running better
(say, due to changing worn plugs), that timing was actually pretty far
off. seems to be an iterative process, with timing set more and more
accurately as engine runs better. fact that digijet timing set with vacuum
adv/retard connected (even though stabilizer bypassed) may be a
complicating factor.

dlk

On Sat, 17 Jan 2004 18:08:22 -0600, Jeff Palmer <icecoldvw@HOTMAIL.COM>
wrote:

>I also periodically have a rough idle in my 85.  This often happens when
>it's warmed up a bit (it's -20C or so today).  I've found that when I
>restart the engine the idle improves.  Same fix as when i have the bucking
>problem (which is very, very rare).  If I restart the car to fix the idle,
>does that mean the ECU is at fault, same as with the bucking problem?
>
>Also, why didn't the factory set the timing to 5 deg BTDC if there is an
>advantage?  Is there a downside?
>
>Thanks
>Jeff
>85 Westfalia GL