Is there a way to set the DLC of a j1939 frame out?
No, the DLC will always be 8 bytes for a JFOUT.
The only J1939 message that will go out with another DLC is the request (RQST PGN 59904, DLC 3) that you send out by using the "poll trigger" on the JFIN.
The request PGN is the only J1939 message I know of that has a DLC that isn't 8.
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