How about using smoke?

https://www.youtube.com/watch?v=mTywIQVOV7k

(Coupled with the vacuum gauge diagnosis mentioned above; you should be able to find most anything.)

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72% 1992 FJ80 + 17% 1983 OM617 + 10% 85/87/92 4Runner + *Eclipse/GMC = 100% Truck
(*<1%)
Build Thread: http://forum.ih8mud.com/threads/a-humble-fj80-om617-r151f-swap.759554/