[T2] weak spark

[accessys at smart.net]

lately the bus (78 auto) has been getting hard to start,. and it has been 
bitter cold so haven't wanted to do much work on it but last week got a 
nice day and ran thru some checks

timing ok
fuel presure ok

but the spark was real eniemic yellow.  so swapped out the coil and still 
phtz of a spark.   I have a high output coil so normally blue-white snap 
but this is horrible.   have full 12v to the coil so has me scratching my 
head.  if I get it started it runs fine plenty of power etc.  but why the 
weak spark...???

have a couple things using the coil plus wire to supply switched power but 
not new so ???  I got a relay but haven't had a chance to install it but 
can't imagine the problem.   have checked all the stuff in the fuel 
injection trouble shooting manual.??

have a spare ECU so considering swapping that in.   but it won't even fire 
with ether most times.   but when it decides to start it starts right up 
and runs fine until I let it sit for a few days.

Fri fired right up and drove some errands worked fine. went out this 
morning and again this afternoon and can't get it to fire.???


ideas????

thanks
Bob