I see Matt hasn't been able to answer this yet, so, from what Bob Wilcox told me, U-ACCEL 2 is the pump voltage the ECU uses during the short open loop period that occurs after the propane shuts off (around 19,000 rpm). It's the only time the system runs open loop.

I don't remember the exact range but both my P-70 & P-80 are set to .750v. If I recall correctly, my Titan was set around .850v.

Generally, if U-ACCEL 2 is set too low, the engine may stagnate, hesitate or accel slowly after the propane shuts off. If set too high, it will blow flames. For instance, I had to run the Titan up to around 1.050v to get it to start the way I thought it should. You should look for a consistent rate of acceleration of the engine.

It's also been my experience that engines that don't accelerate well on start or don't make it past 35K-40K, all else being equal, have a not so good pump. A weak pump is also indicated if the pump will not start or is slow to start at U-ACCEL 1 = .200v indicated by the engine running on the propane only for more than a second or two. In this case, U-ACCEL 1 can be increased slowly until the pump starts reliably.

Hopefully, Matt will get more details.