98 454 Mag Mpi mid range missfire

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05-10-2019 | 04:31 PM

#21

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From: On A Dirt Floor

There is usually a tiny screen under the regulator in most fuel rails. I'd check there 1st. if clogged, the fuel will be deadheaded and will be at fuel pump deadhead psi.
Ck diagram to see it has 1 before you go in.

05-11-2019 | 07:23 AM

#22

AllDodge

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From: KY

I would suspect that the problem is the regulator and or screen (item 16) on the cool fuel module (item 15).

98 454 Mag Mpi mid range missfire

The upper one is another regulator (item 5) but is used as a damper, and there is no fuel return from the rail its plugged (item 11)

https://www.mercruiserparts.com/bam/.../31798/2690/90

05-11-2019 | 07:27 AM

#23

AllDodge

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From: KY

My thought is with pressures that high then the lower regulator is probably damaged

05-11-2019 | 11:12 AM

#24

Sean400

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I’m gonna try and get the cool fuel module out and pull it apart thanks for the input I’ll update when I get into it .

05-11-2019 | 12:17 PM

#25

F-2 Speedy

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From: Midwest & T-Rock

You have 2X the pressure needed, if its that high the injectors wont fire correctly

05-11-2019 | 03:42 PM

#26

RBeyer

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From: Antioch, IL

Quote:

Originally Posted by Sean400

It did not have a pro charger

Can you post a picture of the motor and or boat

05-11-2019 | 08:05 PM

#27

Sean400

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Applied vacuum to this and it doesn’t open is this a valid test and I’m assuming this would cause my excessive fuel pressure.

05-11-2019 | 10:26 PM

#28

RBeyer

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From: Antioch, IL

Quote:

Originally Posted by Sean400

I assume larger injectors cam, roller rockers. From looking into the valve covers I can see crane cam rockers.

Is it a green and white named Yea Rite?

05-12-2019 | 06:44 AM

#29

AllDodge

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From: KY

Quote:

Applied vacuum to this and it doesn’t open is this a valid test and I’m assuming this would cause my excessive fuel pressure.

Vacuum is used to change the amount of pressure on the small end.
Need an air source, gauge and pressure regulator. Apply air pressure to the larger hole in your first pic. Slowly increase the pressure and the regulator should open around 43 psi.