Need Help!!!

[Firemedic724]

I have a 30 foot Rinker with twin 4.3 Litre MPI Smart Engines. Got a 2 beep per minute alarm when underway. RPM Above 4000 sends the starboard engine into guardian mode with reduction of power to 90%. The engine serial number is OM367129 V-6 262 . Had engine scanned, ghost codes came up. All cleared. The only code that keeps coming up is the over rev alarm. We noticed while underway the Throttle position goes into neutral. Cable and TPS switch adjusted. Went out again and still get the 2 beep per minute alarm then full alarm when 4000RPM is reached. Switched TPS from port to starboard and still the same issue. Everything is good on the dash no issues with oil, water temp, or batt voltage. Sea water pressure is perfect. Has anyone ever have this issue?

 

[ctrobk]

You said it is the over rev alarm but does it sound like the engine is over revving? Can you run it on plane with just the faulty engine to see if something is slipping or you are getting cavitation?

 

[achris]

If the neutral switch has failed, and always thinks the engine is in neutral, then you will get an overrev alarm above 3000. Replace the switch, or fix the working, whatever is causing the fault. That will stop your guardian mode too.

 

[Firemedic724]

Switch was switched out with the starboard engine still does the same thing.

 

[achris]

Scan confirmed the switch is being read correctly?

 

[Firemedic724]

Scan shows switch going into neutral then gear while under way. Keeps switching back and forth while under way. This is the switch I used from the starboard engine. The original switch that was on the port side was moved over to starboard side and works fine therefore confirming the switch is not the problem.

 

[achris]

Scan shows switch going into neutral then gear while under way. Keeps switching back and forth while under way. This is the switch I used from the starboard engine. The original switch that was on the port side was moved over to starboard side and works fine therefore confirming the switch is not the problem.

You have a connection or wiring problem then. You need to check the pins at each end and the harness for breaks.

 

[Firemedic724]

I am having a mechanic ohm the wire harness. Could it be an ECM?

 

[achris]

I am having a mechanic ohm the wire harness. Could it be an ECM?

It could, but unlikely. If you can find a problem, swap the ECMs over...Sounds intermittent, like a wire shaking around.

 

[Firemedic724]

I cant swap ECM's because the other engine has a different serial number and my engines are counter rotation so that would cause a bunch of codes.

 

[Bondo]

I cant swap ECM's because the other engine has a different serial number and my engines are counter rotation so that would cause a bunch of codes.

Ayuh,.... Yer Drives might be counter-rotatin',.... But I assure you, the motors are Not,...

Merc hasn't built a right-handed motor since christ was a pup,....

'n of course they're different serial numbers, they're built at different times, 'n no 2 motors use the same serial number,....

 

[Firemedic724]

So it will be safe to swap the ecm's and it won't throw codes if I do?

 

[Bondo]

Ayuh,.... Sure,.... It'll only throw a code, if it finds a reason,...

 

[Firemedic724]

Would a lower shift cable cause this problem? They were replaced last year and ran perfectly fine the whole year.

 

[achris]

Very unlikely.

 

[Firemedic724]

OK, switched ECM's from starboard to port. The problem reproduced itself on the port side. I contacted MerCruiser and they stated to check iac valve and make sure that the output is either 30 or 40. If it is zero or 100 there is a problem. So I switched I iac valves as well to check and see if the problem is reproduced. The Portside engine which is the problem engine shows the iac valve operating at 100. I remember last year I had to replace the iac valve because the solenoid melted. The muffler in the throttle throat where the iac valve receives the air was extremely dirty. Unfortunately, I did not replace that muffler when the iac valve failed because I was underway. My thoughts are since this Iac valve overheated it possibly caused an overheat in the wiring harness and now the harness has to be replaced . Everything has been switched over to the port engine including temperature sensor, electronic control module, and the iac valve. With all of these devices being switched over to the port engine where the problem exists, the issue is still present with the shift position sensor showing the boat being in neutral when it is in gear. A new switch was installed and while the computer was hooked up the switch was depressed and it still showed neutral when it should've showed in gear. What are your thoughts on my findings?

 

[Firemedic724]

A compression test is being performed today on the port engine. Mercruiser stated as the last ditch effort to check the compression. He said it is highly unlikely that it would be a compression issue but wanted to exhaust every avenue before placing an order for a 500.00 wiring harness. As he explained, all the sensors operate on around 5 volts of power and if you have one cylinder that is low in compression, that may cause the IAC valve to activate at 100 to try to keep up. This can cause reduced voltage from other sensors, therefore causing the shift position sensor to fail showing the boat in neutral when it really is in gear. This in turn causes the over rev alarm to activate because the computer thinks it is still in neutral while in gear and the RPM is raised over 3000. This is a far fetch idea but it is the last test that can be done since everything else has been tested. If anyone has any other ideas, I am all ears. I will keep everyone posted. Thank You for your help.

 

[achris]

Disconnect the IAC.It'll flag an alarm, but it will confirm or eliminate the 5v rail as a potential issue.