In a message dated 98-04-13 12:30:38 EDT, you write:

<< My 87 Vanagon will run fine for about 20 mins and then it starts to misfire
and
 lose power ...The misfiring causes the engine to vibrate as if its out
 of balance or one cylinder doesn't fire.  ... If I ease back on the gas, it
sometimes will cause it to snap out of it and run smooth, but usually I'm
climbing and as I give it more gas, it'll misfire again. ... Other data
points: 137K , new heads about 4K ago.  When it runs well, it really runs very
well.  The O2 sensor light came on about 15K ago and I never replaced it.
Thanks for any help.

 Tom Ervolina
 Enterprise Solutions Research >>

Tom--

I'd suspect the ignition system, particlarly the spark plug wires. Make sure
they are all connected well, and there are no wore places on the insulation.

I had this exact problem years ago on a 914. I found it by looking carefully
all over the plug wires while the motor was running in a darkened garage (door
open for air). If this is your van's problem, during the missfiring you will
see a spark jump from the wire to whatever ground is nearby.

How handy that in the van, you could concievable have someone else drive while
you sit in the back seat and gander at the wires!

gmbulley
cary, nc
Sunny, 71 degrees