compression and vacuum leaks also have to be considered.

I've never heard of a sticking valve in a waterboxer engine ..
but that would do it too.

marginal ignition comes to mind..
when ign coils are 25 yrs old, I like to replace them ...
cause they gotta be due ....they don't fail black and white ..
they're nebulous.
 though of course, it it's one cylinder..
you don't think of 'central' ignition things like the coil...

if resistance is high at the one spark plug..
gap is large, plug is tired ..
I have seen many fail to fire across the electrodes, and instead just weakly
fire to the side ..
that could do it.

try this..
when it's acting up ...
running on 3 ..
while it's running, with an insulated spark plug wire pliers...
hold that cylinders plug wire away from the dist cap terminal..
so it makes the spark jump up to 3/8ths of an inch ..
I have seen that make the spark get a plug firing ........or firing part
time.

that's if it's ignition related ..
for sure you should be checking compression and leak down,
and always consider vacuum leaks.

Scott
www.turbovans.com
----- Original Message -----
From: "Dominic Provini Jr." <dprovinijr@HA-PA.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Monday, June 20, 2011 5:18 AM
Subject: Running on 3 Cylinders

Hi,

I have a question . . .My 85 westy is in the shop getting some work done
and the mechanic has been trying to figure out why it sometimes fires on
3 cylinders and sometimes 4.  It's a 1.9l and it's starting to happen
all the time now.  One time I will start it and it will run fine, the
next time I jump in it and it runs horrible.  I have replaced the spark
plug, the plug wire, the rotor and the fuel injector.  Is there any test
he can perform to try and track down why cylinder #1 doesn't fire like
it should?  Any help would be great...

Thanks

Dom