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Dropping revs and O2 alarm again

M

metal-chicken

Regular Contributor
Got our boat back on the water this weekend and when running at about 1800rpm the revs are dropping slowing to about 1400rpm and then jumping back up to the original level - idle rpm are stable but I'm getting an intermittent O2 alarm at idle speed only.

Other than that the engine seems to be running strongly - starts well and anything above 2500rpm seems really stable.

With a new 17" prop it's popping our Outrage 210 straight onto the plane with two people and 100 gallons of fuel on board. It's also pretty good with 7 people and full fuel and can do the same, but a slower, with 10 people and full fuel!

Over the winter I drained the VST, changed the LP filter, external fuel separator and drained the engine fuel separator, but I didn't do the HP filter as I'd read it was a two year (100 hour) thing.
I'm guess that I should have done the HP filter after all as the boat is now kept on a mooring at I'll have to pull it back out to do that filter now :mad:

Any suggestions for the rpm drop/jump back? Could this be related to the O2 sensor which was only replaced last year? I'm guessing that SB56 has been done as the engine is rocking the newer ECU and O2 sensor.
 
The HO2 sensor should not be causing surging, but you never know. A bad HO2 will cause a loss in engine efficiency, running too rich. A good telltale is blackened plugs. I would speculate that if the HO2 sensor had a bad connection and was kicking in and out, that could possibly cause some surging.

The HP fuel filter on these engines is a source of many performance problems. It should be changed annually, regardless of what the maintenance schedule says. They seem to deteriorate all on their own.

BTW - SB #56 does not call for a different ECU or HO2 sensor. However, SB#70 does. for engines in the range BAGJ-1400001 ~ 1509999 and BAHJ-1400001 ~ 1509999.
 
BTW - SB #56 does not call for a different ECU or HO2 sensor. However, SB#70 does.
Click to expand...
Yes I should have said SB#70 - but I was guessing that if the work in SB#70 had been carried out then the work in SB#56 probably would have also.

I believe that the O2 sensor error beeps/lights are shared with low fuel pressure error. Could a deteriorated HP filter cause a low fuel pressure error signal?
I would have thought that it would have also affected the higher speed engine performance, but I can see no evidence of that although conditions haven't been ideal for testing.
I'll pull the boat and fit a new HP filter and if the error persists then I'll get another O2 sensor :mad:
 
You said "Could a deteriorated HP filter cause a low fuel pressure error signal?"

Yes, definitely. In the diagnostics section of the Helm manual it says that if the fuel pressure is out of range, it will through a "1" fault code.
 
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