I suspect you have a harness issue. I read on another forum where someone had a similar problem with their boat going into safe mode. Here are some of the things they had mentioned. I apologize if i'm way off, or reposting something you have already read.
Also, I had experienced something similar with my Camaro after building the motor and installing my Vortech Supercharger/aftercooler. My problem was initially the knock sensor picking up noise from my Taylor wires, and an issue with my harness. After rewiring most of it and shielding and rerouting most of my plug wires my issue was corrected. Again, I hope this helps.
Below is the link to the original post, I have added some snippets of what they discussed on their thread.
99 7.4L MPI will not rev up, runs smooth. [Archive] - Club Sea Ray
"06-26-2009, 02:13 PM
Here's how I'm understanding this. Scenario 1: The ECM is not detecting voltage from the knock sensor and goes into safe mode to protect the engine. Scenario 2: The ECM voltage monitor is continuously receiving a signal from a bad knock sensor and retards timing.
Both situations would result in an rpm drop. The difference is a code will be set only with scenario 1. In Scenario 2 the ECM thinks all is well and does what it's supposed to, so no code.
Does the ECM match the engine? If your original engine had MEFI1 or 2 then you also have a module which shuts off the voltage from the knock sensor to the ECM. This tells the ECM that a knock is present.
Now let's say you throw on a MEFI3, which isn't designed to work with the knock sensor voltage module. MEFI3 works by detecting voltage directly from the knock sensor. This looks like it could be a major conflict, assuming you have the knock sensor module working in conjunction with the sensor. So with the module continuously sending voltage to the MEFI3 ECM (indicating no knock), the ECM would interpret that as a knock and retard timing. MEFI1&2 works completely opposite from MEFI3, regarding the knock sensor. MEFI1&2, no voltage to ECM indicates a knock. MEFI3, a knock is present when it receives voltage."
"06-27-2009, 11:52 AM
Today we found the pin J2-6 (Ignition Control Ref. Low) on the harness that plugs into the distibutor to have a dead short. The grounding out stopped when the rest of the harness was unplugged from the ECM, a Delphi Part. We therefore pulled the ECM for testing. I will keep you posted. I think the problem is in the ECM although no error codes or in the timing sensor.
J2-6 is the pin for Ignition Control Ref. Low on MEFI-1 and -2. It's J2-3 on MEFI-3. It's supposed to be 0 (less than .5) volts and held there by the PCM. J2-6 is not used on MEFI-3.
As above the knock sensor module is integral to MEFI-3. It's external on MEFI-1 & -2. The L-29s use J1-30 and J1-14 to directly connect the knock sensors to MEFI-3. If the ignition wires to the plugs run too close to the knock sensor wires, MEFI can interpret the cross-talk as knock and retard the spark. Use the scan tool to read the number of degrees that the spark is retarded. Should be zero.
Forgot you have a sterndrive. J2-24 is the input from the sterndrive lube bottle. Make sure this circuit (906 tan/white) is not grounded."
"07-07-2009, 01:03 AM
IT IS FIXED....... After checking all the sensors and replacing the cool fuel system as well as all the injectors we finally decided to check the wiring harness and the ECM. Unfortunatly we were not able to find a good used or new MEFI 3 wiring harness to try with my existing MEFI 3 ECM with so we ended up trying a MEFI 2 harness and MEFI two ECM and that it was it. The boat is running great. Finally...What I need to do now is source a good used or new harness for my 99 7.4L MPI engine and try it with my MEFI 3 harness. If that still leaves a problem I will need to also track down a MEFI 3 ECM. The good news is I now have a running boat. My mechanic wants me to put on the MEFI 4 kit which is a new harness and ECM as a kit, as Mercruiser no longer makes a MEFI 3 available as DELPHI the manufacturer no longer makes them. Anyone have experience or thoughts on going to MEFI 4."
"09-13-2010, 12:43 AM
Wanted to put in a final comment to close this thread but let future readers know the final solution was not the ECM. I found a used harness on EBAY for the MEFI 3 and voila! Engine ran great. No obvious visual problems looking at the harness but I suspect a broken wire or faulty connector would fail once the RPM came up and the voltages increased. Hugely hard to troubleshoot. Older engines using EFI opens up the engine to major corrosion headaches. Moist environment and electronics, not such a good combo. Thanks again to all who helped me with this."
Nick
Re: Winter Upgrades
