MerCruiser 7.4L 310HP Running Rough and throwing code 43 Continuous knock
 

Last year I feel the boat was running well, not bad, It was running rich and when I would rev the engine it would almost always die when it got back to idle unless I gave it a little gas. I never checked for any codes or anything like that. The engine coupler went out late last year and I got it fixed last week. The mechanic said the boat was running rough and throwing code 43 continuous knock detected. (This is after unwinterization). Do to the short time frame and the distance I had to drive to pick the boat up from the mechanic I figured I would try to resolve this issue myself. At idle when on the scanner it did not show up that it was knocking. When we took it out on the water and I started getting on it it started showing knock and retarding the timing. it did feel more rough then I remember, but it is hard to tell since it had been 5-6 months since driving the boat. When we got back to the dock the transom was covered in soot. I had a 9 hour drive ahead of me so we loaded it on the trailer and I brought it home. I have bought new plugs and wires since they needed replaced and plan on finishing this up tonight.

The Cap and Rotor were replaced by the mechanic, but only after he started it up with my cap and rotor on it so I dont believe it is timing related. The service manual says to check the Knock Sensors next. I dont know how often these go bad..



Has anyone had this issue before?

Any Ideas?



More info : The boat has 246 hours on it and the scanner showed that also. It is in a 2000 Baja 272 and last year on GPS it was able to run 59mph with a Mirage 23P.

Timing is the first place I would look, put it in service mode and see where it is, obviously its running fat..........there's a single wire going to the sensor from the mpi harness maybe it came off its a weird connector

I no longer have access to a scan tool.. Any idea what they cost?

Alot of these mechanics seem to have been fumbling firing orders lately . J.s..
And going outside of 18436572 the right wrong way can get full knock retard also

Is there a diagram on where the wires are suppose to be on the cap and on which plug?

Thunderbolt ignition?

I believe it is the Delco HEI.

You can make a code reader with a resistor type LED and a paper clip. Find the DLC connector and insert the LED (radio shack and the like) , then insert the paper clip. Turn ignition to ON (don't start) and count the flashes.

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Your running rough and have soot, Yes check timing

Would be best to have a serial number but being a 2000, it should be Delco EST. Timing should be 8 BTDC, plugs MR43LTS at 0.045 gap

Doesn't matter which wire is started where, only that the firing order is correct as airjunky posted. Distributor rotates clockwise when looking down from top

Also, the knock sensors do go bad, but not that often. Find the blue wire connected to the sensor below the exhaust on starboard side and make sure it is NOT tie wrapped to the plug wires. The plugs firing will set off the knock module

Im sure there are some good videos on youtube on adjusting timing... never done it before.. Looking at the service manual it looks pretty intimidating. Any tips?