I'm NOT a mechanic.....

but I do have an 84 Westy, and what you are describing sounds to me like a
dodgy connection to the Oxygen sensor.

When I had my sensor disconnected, I had a large loss of power, and a very
rich, smokey exhaust - from the computer no longer being able to calibrate
the air/fuel ratio properly.

Other listees, with greater knowledge than I will steer you along a finer
path.

Regards,

Marshall Ruskin
84 Westy

>About 4 months ago I bought a '90 Vanagon Carat and have recently
>experienced problems which the previous owners had experienced in '96.
>When going up a long hill after about 1/2 hour of driving the van
>suddenly loses power (ie. the gas is floored and I can't go above
>40mph).  I have taken a couple of day trips and one 3 day trip from San
>Francisco to Cambria down the coast and back up.  I experienced no
>problems on this trip however is was raining and quite cold the whole
>time we were driving.  The problem first occured three weeks ago taking
>a trip into the valley where the temperatures were warmer than the usual
>SF cool.  While going up a hill there was a sound like a cork popping
>and then a great decrease in power as well as the engine sound dropping
>from its normal hum to a very low hum.  Shortly after this, black smoke
>began to come out of the tailpipe.  It was a very long 2 hour drive back
>home with the black smoke and the car topping out at about 45-50.  We
>then stopped for about 20 minutes after which the car was fine.  My
>mechanic looked at it and said he didn't know what it was.  Today I went
>out again to a warmer area with a spare computer, and of course this
>happened again, and swapping the computers didn't help.  Does anyone
>know what this problem could be or does anyone know of any materials
>other than the Bentley book that I could get on Digifant systems.
>Any suggestions or info would be greatly appreciated
>Amy S.
>