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Mercruiser 454 Magnum MPI running cool and rich

Old 08-02-2017, 09:29 AM
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Originally Posted by 715517
Injectors are Keihin 5LDJ!
where did you get that from?, do you have a picture, if they are the 2.750" ish long they are mefi1, not mefi3
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Old 08-02-2017, 10:53 AM
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Injector on right is a mefi1, left is mefi 3, which one do you think you have?
Attached Thumbnails Mercruiser 454 Magnum MPI running cool and rich-20170802_114748.jpg   Mercruiser 454 Magnum MPI running cool and rich-20170802_114754.jpg  
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Old 08-02-2017, 11:33 AM
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I have some pictures in my phone, when i removed and inspected the injectors. They are definetely those bigger ones. And big Keihin logo on the side.

Engine is 1998 454 mag mpi, first modelyear with serpentine belt, and i've been told that it had an ECM where was two connectors on one side like MEFI3 does. Now it has connectors like MEFI1.
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Old 08-02-2017, 12:54 PM
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Originally Posted by 715517
I have some pictures in my phone, when i removed and inspected the injectors. They are definetely those bigger ones. And big Keihin logo on the side.

Engine is 1998 454 mag mpi, first modelyear with serpentine belt, and i've been told that it had an ECM where was two connectors on one side like MEFI3 does. Now it has connectors like MEFI1.
i just did some work on a 98 powerquest, had mefi1 502 w old style injectors but had serpentine and cool fuel, was sorta crossover year, yours was probably always a mefi1 if it has old style injectors, there was never a mefi3 w tall old style injectors i have ever seen, Smitty
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Old 08-02-2017, 01:32 PM
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Rereading you first post again knowing you have old style injectors, old style mefi1 ecu aside from fact it may have a 502 program on 454 the fact it had a ect code after you have changed ect sensor makes me wonder if you have a circuit problem w ect wires, i dont remember if the hotter it gets the lower the resistance is or vice versa. Lets say it is grounded or partially opened, whatever it would take to tell it its NOT warmed up it could revert to lowest number in earm up chart and ad 18% more fuel. You could locate the ect wires in j connector at ecu and test for open, short, ground, continuity etc in 20 minutes w a vom, prob what i would try, its free, Smitty
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Old 08-02-2017, 01:35 PM
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Since a boat will never be running when its 0c or -20 I always change multiplier to 0 in those boxes in case a sensor did go bad or wire opens/grounds out, fwiw
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Old 08-02-2017, 01:48 PM
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I have already measured and inspected the wires for ECT and MAP-sensor, they're ok.

Tomorrow im going to the boat and trying a new temp gauge sender with resistance 100F=450ohm. (Faria gauges need this kind of sender) The old one was 100F=1450ohm so i think that was the reason i got only 120-130F temperatures to gauge.

Im also trying new TPS sensor, that`s the only old sensor in this engine

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Old 08-02-2017, 04:04 PM
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Just a note, the intake and fuel rail could be from a MEFI-1 setup and the harness is from a MEFI-3. Reason being is I have this setup on mine
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Old 08-02-2017, 05:40 PM
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Originally Posted by AllDodge
Just a note, the intake and fuel rail could be from a MEFI-1 setup and the harness is from a MEFI-3. Reason being is I have this setup on mine
The fuel rail and lower intake manifold would have to be from a mefi one to use those early injectors as the rail is much shorter on the Down legs and injector holes are different on lower because of those giant rubber washers and lack of oring
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Old 08-02-2017, 06:52 PM
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A MEFI 1 fuel rail using the VST is totally different than a MEFI 3 using GEN 2 cool fuel - fuel rail

Also the fuel pressure regulator is mounted on the Fuel rail for MEFI 1 VST that use the tall fat fuel injectors from Japan.

Mefi 3 fuel rail the fuel pressure regulator is mounted in the gen 2 cool fuel system.

The tall fuel injectors MEFI 1 have an inherent problem that I discovered years ago and another issue I discovered 7 months ago.
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