377 Mag Bravo 3 DTS Re-Power electrical problems

I purchased a 2009 377 Mag MPI Bravo with DTS. Engine Serial number 1A344800. Trying to figure out if the PCM is shot.

I called Mercruiser tech line, gave them my engine serial number and they gave me the part numbers to purchase the correct Smartcraft harnessing kit to rig my boat with.

After installing the new rigging, I took the boat in to a certified Mercruiser dealer to get them to program the new Smartcraft / DTS harness. They were unable to complete the set up and could not get the engine to start.

Brought the boat back home and found that the only way the engine will start after powering the key to the on position is to remove the start relay and jumper between the red and the yellow/red stripe wire momentarily to crank the engine. This starts the engine and it will run until the key is turned off.
I have swapped out the relay to make sure it was ok. I have verified that the shift position switch is working.

It would seem that the PCM is not sending a start signal to the start relay when the key is put in to the start position but I can not figure out why.



I'm stumped.

Anyone have any idea's?

I could be all wrong here but I don't think the ECM has anything to do with the starter circuit. On EFI engines, turning the key to RUN before you turn to START initiates a fuel pump event. But when you turn key to START all power from key switch is directed to yellow/red wire. The yellow/red wire only activates the starter solenoid. I would test the wire by disconnecting it and put a test lamp or multimeter between the wire and ground and turn the switch to START. You should be getting voltage.

If the engine computer was no good it wouldn't run. Seems like it's all god except for the starting thing. Maybe a new keyswitch?

PS your dealership is a bunch of doofuses

o2batsea said:

I could be all wrong here but I don't think the ECM has anything to do with the starter circuit. On EFI engines, turning the key to RUN before you turn to START initiates a fuel pump event. But when you turn key to START all power from key switch is directed to yellow/red wire. The yellow/red wire only activates the starter solenoid. I would test the wire by disconnecting it and put a test lamp or multimeter between the wire and ground and turn the switch to START. You should be getting voltage.

If the engine computer was no good it wouldn't run. Seems like it's all god except for the starting thing. Maybe a new keyswitch?

PS your dealership is a bunch of doofuses

Click to expand...

Agreed on the dealership. The engine has a relay on starboard side of the intake manifold that has a red power wire and a yellow/red stripe on the normally open contacts of the relay. The coil on this relay is activated by two wires that come directly out of the ECM. The relay tested good but is not getting a signal from the ECM to activate when the key is in start position. There is voltage on the start terminal of the ignition switch when in start.

I doubt the ECM activates that relay. I may be wrong but I think those wires only inform the ECU that you are trying to start it. The engine management on these is fuel-only as they still have distributor, yes?

Maybe after Chris has his coffee, he will jump in here and tells what to try.

I'm thinking because its DTS and Smartcraft, all engine management is from the ECM. As mentioned, There is a power wire (Red) to the common contact on the relay, there is a yellow/red to the normally open contact on the relay. The only other two wires to the relay are wired through the engine harness directly to the ECM. The only way that relay can activate is if it has a voltage signal from the ECM.

The ECM does control starting on a DTS engine with Smart Start.

Sounds like something was missed during the install. Possible bad terminator/Jbox/command module on CAN X.

If the network is showing all modules and everything is installed as it should be and the command modules have been programmed and a Lever adapt was done, you may be replacing the ECM.

Thanks Chris, in talking to Mercury tech line and your post. I now know that the dealer I took it to originally was unable to program it and troubleshoot it correctly. I believe the ECM is fine, the only problem is the G3 setup procedure still needs to be done properly otherwise the ECM will not send a start signal to the start relay. Thanks for the replies. I've found another dealer to take it to however 3 week wait. I will update if all goes well.

It is a 10 minute job to program the whole system. After the lever adapt is done and the command modules check the ECU and it verifies Neutral, the engine will start.