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Check engine light @ 3,000 rpm 8.1

S

slow cruiser

Regular Contributor
Crusader 2001 8.1 450 hours. Starboard runs great. Port runs fine 'til 3,000 rpm then check engine light and alarm go on. Stop the engine, starts right up, all gauges are right on spec. It happened last year then I cleaned the grounds and filters and it ran fine. Took it out this year and it started again. Below 3,000 it runs fine, starts right up hot or cold. Does not set a code. Any idea??
 
if the CEL is on and the alarm triggers, a measurement made by the ECU has been deemed in violation and you may need a scantool to understand why.....
 
Fine, but there are no readings out of spec on the scanner whether the MIL is on or not. What do I do next? This seems to be rpm related as the warning only goes on at 3,000 rpm, even though the engine continues to run fine even when I run it up to 4,000 rpm with the light and buzzer on. Seems more like a sensor is malfunctioning than the engine is. (CEL is new to me, all the Crusader manuals I have use MIL.)
 
slow cruiser said:
Fine, but there are no readings out of spec on the scanner whether the MIL is on or not. What do I do next? This seems to be rpm related as the warning only goes on at 3,000 rpm, even though the engine continues to run fine even when I run it up to 4,000 rpm with the light and buzzer on. Seems more like a sensor is malfunctioning than the engine is. (CEL is new to me, all the Crusader manuals I have use MIL.)
Click to expand...

Could very well be sensor but that's what the ECU 'reads' to assess what the 'engine is doing'.....I'm a bit baffled that nothing changes (sensor readings) but the light turns on and the horn goes off....
 
I agree, plus no code and the engine continues to run fine. I have taken all readings off the scanner with the alarm going and they are all good. Plugs look good, all are identical.
 
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maybe there's something specific to that tune for that engine.......do you know which ECU is used (either the MEFI-x or the GM part number)?

Also, when the alarm turns on, is it continuous or is there a pattern to it?
 
MEFI-4. The alarm sounds continuously until the engine is shut down. The engine will then start up like nothing ever happened. Repeat. When I took the scanner readings with the alarm going we were holding cruise @3,100-3,200 rpm, readings didn't change. Just sounds like a sensor stopped communicating with the ECU but the ECU didn't react other than the alarm. Once I ran it with the alarm for 10+ minutes, shut it down, started it up and it then ran fine up to 3,400 rpm and we cruised.
 
I hear you but - the ECU shut down the engine for a reason and that reason is very possibly coupled to the alarm sounding as well....

Do you have the values before the alarm sounds, to compare with them after the alarm goes off?? Many of the programs in the ECU will switch to a default value if they detect a fault....also, there are a handful of discrete inputs to the ECU on a MEFI-4 that can also trigger the alarm....these are separate from the sensor inputs. The factory service manual will have specifics for your 8.1; if you don't have one, search the web and you can find the Delphi (GM) original that the marine OEMs use as a baseline..
 
To clarify, the engine does not shut down, I shut it down. It runs just fine whether the alarm is activated or not. The only inputs shown in the manual other than the sensors are 'general warning 1' oil pressure and '2' transmission temp.
 
beats me.....only other scenario I can develop is the harness to the panel has two shorts in it....not likely but possible.....

Maybe Chris has opinion...????
 
I would hate to mess up one of these, is there anything special about moving them? Disconnect power first, handle the connectors carefully.
 
nope....you got it - and move the connector by the shell, not the wires going into it.

You can double check the manual to make sure....but they are pretty robust....

if you do the swap temporary, there aren't any concerns. if you swap them and opt to leave it, the 'history' in the ECU won't apply to the engine connected.....mostly operating hours segregated by RPM bands...there's no fuel trim to 'relearn' as there are no O2 sensors....
 
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