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Mercruiser 377 mag

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robert10

New member
Hi Guys
Have a mercruiser 377 will not run up to wot and sounds very boggy at idle feels like over fuelling as very fuel laden exhaust. Have changed plugs which had been running rich also changed cap to verify no crossfire, fuel pump pressure good, no fault codes. Anyone any suggestions.
 
Cheers checked filter in fuel pump module no water small traces of crud from tank but no great amount checked new plugs and running very rich even off load
 
get a scan tool and check the sensors the ECU scans....could be one is "wrong" but not out of the allowed range which is why no code has been set....ECT sensors used to be guilty of this...
 
Thanks for the two suggestions would the iac valve affect wot or even cruising speeds? The ect sensor would fool the engine into running cold however now leaning toward injector problem maybe the particles found in the filter chamber have found there way through as have noticed no 1 & 2 plugs very wet and fouled compared to the others to the extent of a danger of washing out those cylinders.
 
Injectors aren't fond of dirt...and a leaking one can cause wet plugs as well as a "hard to start" condition, especially after a hot soak...you can replace them or get rebuild (exchange) what you have... a good scan tool will have a cylinder power balance test...
 
Yes it is the injectors pulled them out and tested with a 9 v supply and pushed a bit of powertune through them seems cyl no 1 & 2 are particularly bad blocked nozzles and not a good spray pattern. Our distributors have no stock at present so will try a clean and see how we go
 
robert10 said:
Yes it is the injectors pulled them out and tested with a 9 v supply and pushed a bit of powertune through them seems cyl no 1 & 2 are particularly bad blocked nozzles and not a good spray pattern. Our distributors have no stock at present so will try a clean and see how we go
Click to expand...
I would recommend verifying that your fuel pressure is within specification.

Did any of the debris happen to look like some sort of paint material?
 
Hi yes fuel pressure was ok within spec at all off load revs, injectors were the problem the cleaning has done the trick.
the debris in the injectors appeared to be black speckles.
 
Good you got it resolved...just so you know, when you test the pressure in the rail, you need to do it with the engine under load...
 
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