OX66 code 42 (Overheat control/oil empty control) Request for expert advice

[IFish4Tuna]

Hello - I am helping a friend with twin 1998 250HP OX66 on a GW Marlin 30'. I also have 99 Yam engines on my Bimini 306, and have done a lot of my own repairs so helping him. I have service manual for my 99 engines, and blinky tester. Have about 20 hours of diagnosis into this issue. I got involved after a few parts had been swapped, and began to focus on testing instead of replacing. Need expert advice please.

Problem Description :

• Can't get above 2000 before Port engine bogs down to around1800 RPM
• There is no audible alarm when this occurs, just limiting.
• Ran the blinky test under the condition and it its throwing code 42 (Overheat control/oil empty control)
• Gauges blink all 3 oil indicators when fault occurs.
• Temperature indicator is NOT showing any fault
• When turning on key (without engine running) - Port Engine key switch has audible alarm for about 90 seconds then stops alarming. This is odd because the oil tank on engine is already full.

Diagnostics / Replacements Done So Far :

• Eliminated the twin engine key switch assembly and have separate key wiring (from a Yam tech) so that the problem only affects the root cause engine. So it is definitely port engine. This also results in only 1 engine being limited. The faulty engine.
• Remote (large) Oil Tanks are 1/2 full
• Engine oil Tank is Full
• Performed continuity test at the engine oil tank sensor. Tested SW C (lower) Blue/Red and Black. Circuit is open, indicating that it is not commanding pump / alarming. This is expected because the tank is full.
• Performed continuity test at the engine oil tank sensor. Test SW A (upper) Blue/White and Black. Circuit is closed, indicating pump is commanded to stop. This is expected.
• Performed continuity test at large oil tank. Testing for oil level. Black and Black/Red. It tests positive for tank being more than 1/3 full.
• Performed continuity test of large oil tank at the 4 pin harness on the starboard side of engine, and testing Black and Black/Red . It also read a closed circuit. Indicating the tank is more than 1/3 full, and also validates the harness at the fill tank is performing properly. The next path of the wire after this connector leads to the CDI.
• Swapped engine Oil Tank Sensors from Starboard to Port / Port to Starboard
• Swapped CDI Units from Starboard to Port / Port to Starboard
• Replaced Thermostats
• Replaced Pulser Coil
• Replaced Low Pressure Fuel Pumps
• Replaced Stater
• Cleaned VST Filter
• Filter leaving VST tanks cleaned
• High Pressure Fuel line tested for proper pressure

Questions :


There is no audible alarm when this problem occurs. This seems to imply it is not due to low oil (SW C). So could the flashing oil indicators be an anomaly related to a different limiting/governing problem? My friend said he has checked temperature with hand and the engines are not overheating. Also no gauge indicating temperature problem.

I'm stumped. Could really use some advice on what to test for next and why. Running out of ideas of what to check for.

Thanks in advance, Ed

[boscoe99]

Is the alarm system (the buzzer) known to be working?

Three lights flashing means that there is a low voltage situation. Low voltage to the CDI assembly.

Could be defective wiring, a loose fuse holder, excessive voltage drop across the fuse or ...

Monitor voltage to the CDI assembly at the CDI assembly and see if battery voltage is maintained there or not. Would not hurt to inspect the CDI assembly grounds as well.

[IFish4Tuna]

Thank you for such a quick reply. I'll get answer to the buzzer working question. I am not sure, but I believe so. As for where to test CDI incoming voltage. Do you mean test at the fuse holder leading to the CDI as shown in this image? What would you use for a ground to the tester's lead? I have not been into the CDI so I'm not sure where those grounds are.

[boscoe99]

I mean test for voltage anywhere and everywhere between the battery and the CDI. The ground can be any clean point on the block.

[Keithbaja]

Not gonna stick my head out on this one !! But, to do diagnostics on these things. You must have a clear, precise order of testing. From the mad post you wrote. I sea no mention of fuel flow ( volume) presser is a great thing. But also need volume.. I would stand back for a day or 2 start early with a solid plan of testing . IMO this sounds like u over kill
Most of the time it's a simple 1 item that fixes the problem. Those are Great motors in my opinion. If you where closer I'd give you a hr
Sometimes a fresh set of eyes can help
Don't fall into what you have changed, but what have you missed. Wish you fast success and Tight Lines

[Keithbaja]

Thanks for your time to reply !! NOT,, It's sounds like your running out of fuel.. U think it's going into limp/protect mode. WHY ??

[IFish4Tuna]

Hello - sorry for slow replies here. I have been busy with work and as mentioned the boat is not mine. I am helping a friend. Since the last update a number of additional diagnostics were performed by a Yamaha Tech. (I do not have the list yet from my friend yet). The one odd item is that as an experiment the Knocking Sensor was disconnected and the problem of engine going to limp was not exhibited. A new sensor was put in, and the problem re-appeared.

The voltage to the CDI was tested and it was good.

Once the list of subsequent diagnostics is available I will post.

Also if/when we ever figure this problem out the problem WILL be posted for others to benefit from.

Ed

[99yam40]

knock sensor saying there is a problem and retarding the timing should be easy to verify with a timing light

[Keithbaja]

It's 2 in the morn. And a coyote or mountain lion work up my girl (dog) now I can't get back to sleep ! Grrr
Do you have the blinky light and know how to hook it up on the oil tank wires ? Engine tank. If mem served me right,, it always kicks out a 12 code for retarded timing then any DTC's. Simple, GOOD motor.. throwing parts blindly sounds like this FAKE covid BS
.your gonna get anywhere.. G'ni mate's,, this Capt is out

[IFish4Tuna]

Yes on blinky. Results of that are in the opening comments. I think next step is to check timing.

[99yam40]

Yes on blinky. Results of that are in the opening comments. I think next step is to check timing.

bad gas will cause knock problems too