Is the problem just after a "long extended" drive or is it after the engine
warms and goes into "closed loop" operation? If the later what you are
probably experiencing is a lean cylinder misfire. Look for anything that
causes the engine to have an un-balanced air fuel mixture. Vacuum leaks, bad
injectors, and valves or guides.

If the problem only occurs after an extended drive look for fuel system
vapor lock, poor pump performance when the fuel gets warm, or the
cylinders/spark plugs are getting heated and you just aren't hearing the
knock and ping. Over advanced ignition timing or the wrong heat range spark
plugs will contribute to this.

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
John Reynolds
Sent: Thursday, October 3, 2013 1:24 PM
To: vanagon@GERRY.VANAGON.COM
Subject: misfire when hot

My vans seems to run just a bit off after cruising for an extended period of
time, say 3 or more hours. Misfire is actually too severe a term; it just
doesn't seem quite as smooth as it is in the morning. I definitely will
notice how well the engine runs the next morning on a trip for example.
Note, my coolant temp is fine.

Van has new NGK plugs, OEM wires, new Bosch rebuilt dizzy and a new Bosch
coil, as well as recent Bosch cap and rotor, so it seems that the ignition
system should be A-OK. Timing set per TenCent's method. I checked for vacuum
leaks, spraying brake cleaner (although engine was cold) and did not find
any - but I am still think that is a possibility.

The blue coolant temp sensor was replaced 6 years and perhaps 10-15,000
miles ago.

Any thoughts on what to check?\

John