Mercruiser alarm & engine stumble

[DC20]

Ok, second time out ever on the new to me boat. 2005 300 MAG MPI (0W3404402) with Bravo 3. After coming off plane to no wake zones, alarm will sound for about 1 second and engine will stumble (once it did stall but started back up immediatly) . I watched the gauges each time, temp good, oil pressure good. Drive lube is full.
Engine has had oil, filter, fuel filter, plugs, rotor, cap, sea water impeller, thermostat. The fuel is maybe 3 weeks old, I did add Mercs new Quickare to the fuel before going out this am. It did not do this the first outing, the thermostat was changed out after the last outing as well.
Your thoughts???

 

[dubs283]

Re: Mercruiser alarm & engine stumble

to find out for sure what the alarm is, you will need to connect to a cds and look at the fault codes

wild guess, iac (idle air control) valve could be having issues and setting a fault

 

[burp]

Re: Mercruiser alarm & engine stumble

Was the alarm a constant alarm or a 2 beep/minute alarm? An IAC problem will generate a 2 beep/minute alarm. Rough idle, varying/uneven idle speed, stalling at low RPM's, and starting problems (engine may start if idled up) are symptoms of a defective IAC valve. There are quite a few problems which can cause the 2 beep/minute alarm. To identify the problem causing a 2 beep/minute alarm, you will most likely need to have the errors read out as it can get expensive guessing and throwing parts at the problem.

 

[DC20]

Re: Mercruiser alarm & engine stumble

Just one beep after coming off plane and a bit above idle.

 

[dubs283]

Re: Mercruiser alarm & engine stumble

when was the last water pump impeller change??

the reason i ask is some of the new style water pumps have pressure switches and if the pressure drops below a certain threshold, an alarm will sound

when you are throttling back, the pressure supplied by the pump may be dropping just below the threshold momentarily, causing the alarm

again, you will only know for sure what the fault is by connecting a cds and reading fault codes

 

[DC20]

Re: Mercruiser alarm & engine stumble

Well just to bring this up to date.
Mechanic said it was the IAC valve and replaced.
Went out again and same thing, now he said it has low water pressure going down to idle. He took it for a water test and of course NO alarms but pressure was low. Will the low pressure cause the motor to die or stumble and an alarm go off? Impeller was replaced less then 10 hours ago.
He wants to go into the water pump and check the impeller (more money).

 

[DC20]

Re: Mercruiser alarm & engine stumble

Ok, mechanic did 45 min. water test, no alarms everything was good. My previous alarms were all low block pressure. Mechanic suspected impeller. Took apart pump today out of curiosity, looks fine to me. Could whatever caused my mysterious low block pressure disappear or should i be looking elsewhere?

 

[Fun Times]

Re: Mercruiser alarm & engine stumble

Those deep grooves in the brass housing will set off the alarm just as yours did.

You could try removing the grooves by resurfacing the back plate, That may help stop the alarm, But if the rest of the housing is grooved up like that where the impeller is, then it's time for a new impeller housing.

The average life span of the brass housing seems to be about 300 hours max And they are not cheap to buy.

Good luck with it.

 

[DC20]

Re: Mercruiser alarm & engine stumble

Yea, there are groves top and bottom in housing. Looks like $315 for a whole new pump without air fittings. Do I have air fittings???
Thanks for the info Boat Tech.

 

[dubs283]

Re: Mercruiser alarm & engine stumble

Do I have air fittings???

no...

replace the impeller...leave the pump housing as is, you will be fine

and continue to replace the impeller at least every third season as per recommended by the OEM service manual