KAMD 42 P-A 1996 - Super Charger will not engage

by Jason
(OBX, NC)

Hell. I'm having a problem with one of my KAMD 42 engines. The supercharger will not engage at all. Starboard engine is just fine. This one was working great too until put her on the hard for a few weeks to address some outdrive issues. Put her back in the water and it won´t spool up at all, at any RPM.

I´ve read the troubleshooting section in the wiring diagrams workshop manual and it was pretty limited in scope to say the least. Here´s what we´ve done so far...

1. We swapped the speed control relay between the engines, and the problem didn´t follow, so we´ve effectively eliminated the relay itself.

2. We applied 12+ to the red wire and grounded the white wire and the supercharger´s solenoid clicks on and engages the clutch, so we think we´ve eliminated the supercharger itself, but we didn´t do it while the engine was running, so not 100% sure.

3. Checked the belt and the tension.

4. Checked the signal coming from the RPM sensor. I have no idea what the correct reading should be, but it´s showing a frequency roughly half of the engine RPM which is the same as the one on the starboard engine, so I´m assuming it´s correct.

5. Checked the resettable fuse in the electrics box and it is good.

Based on all this, I´m assuming its a wiring issue and so we started to check the wiring so...

6. Verified that the red wire is getting 12V+ from the relay.

7. Tried to

check the function of the the white wire from S1 on the relay. This is where I´m getting stuck... The way I understood the operation of the relay from the description in the workshop manual is that between the RPM´s of 1800 through 2400ish, the S1 will connect the white wire to ground completing the circuit to engage the supercharger clutch. HOWEVER, when I test the white wire for continuity to ground (the engine block in this case) it ALWAYS has continuity to ground regardless of RPMs or if the engine is running at all. If I check the voltage between the white and red wires I get 13.4VDC.

I thought there was something to this, but it turns out that the starboard engine exhibits the same characteristics, so it turns out my understanding of how this circuit works is incorrect and I´m hoping some folks here might be able to help me understand it so I can continue troubleshooting.

If I connect both the white and red wires to the clutch, nothing happens, even though I can measure that the white wire reads less than .2 ohms to ground. However, if I disconnect the white wire and then connect the clutch side of it directly to ground (in the same spot that I checked the white wire from the relay for continuity) with a jumper wire, the clutch engages. What gives? I´m clearly missing something in how this relay is operating.

Any help y´all can provide is greatly appreciated. Thanks in advance for your assistance.