DDEC II to DDEC IV Jake issues

Without being right there to see all that was done, sounds like a engine sensor incompatibility issue, to be more specific , engine timing sensor behind the air compressor or the tach sensor on the bottom of the bell housing. Sensors are expensive so throwing money at parts can be a problem but lost work can be too, should hook up a Prolink diagnostic to it , got to be some codes

 

Ok, just read the instructions on the conversion. This is the touchy part, making sure the tech guy did the wiring on the cruise switch correctly or did it at all, I know, has to be approached with the right attitude on that one. Be that as it may, this wiring must be done correctly, there are two micro switches, one on the clutch pedal and one on the brake pedal. Both are tied into the circuitry for the cruise AND the jakes at one point or another. If this wiring modification that the instructions discuss is incorrect then it will back feed to another circut, thus , the ECM will pick up on it and throw the malfunction light. This is a more likely senario than sensor incompatibility as mentioned in my first response; even so I would not rule that out. I would first confirm the cruise wiring mod mentioned in the instructions was done according to the tables provided, then if the problems persist move on to the sensor compatibility angle. It can only be one of the two things, the DDEC2 , 3, and 4s were pretty simple straight up systems, hope this helps get you in the right direction.
J-J

 

hi

I did DDEC-II to IV swaps. Plz pull ECM fault code. ANd check for Jake valves wiring. it may differ a bit