Fire Commander Problems DDEC III
I am working on a Detroit Diesel Fire commander. The problem I am having is it will not go into pressure mode. This is on a 2001 Spartan chassis with Smeal Body.
This unit was replaced about 6 months ago and has had problems from day one. The old fire commander that it replaced also had problems switching modes, but the INC and DEC buttons were the only buttons that worked, so we figured the mode button had gone bad.
I have tested the I/Os, pressure transducer, and wire harness, and I have all the signals that I need to allow it to go into pressure except the signal returning from the DDEC III ECU after the mode button is pressed.
Now, here is what is weird. If the truck is in pump and not running, The commander will switch modes, which says to me the signal is getting to the DDEC and Returning, but once the engine is running, the signal that allows it to switch to pressure is lost and once again I cannot switch modes and it sets its self back to RPM.
Also, the Tach in the instrument cluster sometimes works, and sometimes doesn’t. Could this be related? The Tach on the fire commander reads correct all the time.
Thanks for your help in advance!
DDEC III and Electronic Fire Commander
While the issues with an isolated battery, as stated in previous posts, can cause the problem you have, I doubt the truck has an isolated battery for the DDEC. By 2001, most manufacturers were not using this due to all the problems experienced in the early 1990's.
I would check the ground for the Fire Commander first. It MUST BE GROUNDED TO THE BATTERY. Too many vendors were guilty of grounding pressure governors to the pump panel or pump module structure. A rule of thumb is that the governor and the engine ECM must share a common ground. The best place for this is directly to the ground post on the battery and the ground wires touching each other on the same post. I know it sounds like overkill, but I have fixed many governors of differnent brands just by ensuring that the govenor is grounded properly.
Since the problem appears when the motor is running and clears up with the motor not running, grounds would be suspect. Poor alternator grounds can generate noise that can corrupt the signals to the ECM. Next, check the J-1957 Data Link. There could be excessive noise in the data link that will disrupt the signal. If you have a laptop with DDDL diagnostic program, you can watch the data on the ECM and see if you see something fishy. It could be something not related to the engine and governor that also shares the J1587 data link. I believe the tach on the instrument cluster is also driven by the J-1587 data link, but I am not completely sure on that.
Finally, if the governor has been damaged so that water can seep into the governor panel, it will cause the same problems that you are seeing. Water and electronics do not play well together.
You are correct that the ECM must be properly programmed for the EFC to operate, but that should not be an issue unless someone has changed the program or the ECM was replaced and not properly programmed.
On DDEC III, the J-1587 data link will not always set a Diagnostic Trouble Code.
I know this is a lot of info, but check the ground first.