Im pretty sure Frybrid is less than 12 years old :-)

I can help you out here. your setup is similar in plumbing to that of a Greasecar system - Return line is fed back into the feed line. The advantage is that this keeps the WVO hotter, the downside is that purge times are much longer (30-60 seconds instead of 7-14) and some WVO gets into your diesel tank.

At some point the Frybrid system included an option for a third valve (this is what I have). It gives you the best of both worlds.

Can you send a pic of the black box microcontroller that you have?

Also, the Frybrid manuals are here
Frybrid Vegetable Oil Fuel Systems -- Manuals

Hope this helps to start...

dd

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car