Offshoreonly.com

Offshoreonly.com (https://www.offshoreonly.com/forums/)
-   General Q & A (https://www.offshoreonly.com/forums/general-q-20/)
-   -   98 454 Mag Mpi mid range missfire (https://www.offshoreonly.com/forums/general-q/360479-98-454-mag-mpi-mid-range-missfire.html)

SB 05-10-2019 04:31 PM

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. :)

AllDodge 05-11-2019 07:23 AM

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

https://www.offshoreonly.com/forums/...issfire-3.html

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

https://cimg9.ibsrv.net/gimg/www.off...c219acf3ba.jpg

AllDodge 05-11-2019 07:27 AM

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

Sean400 05-11-2019 11:12 AM

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 .

F-2 Speedy 05-11-2019 12:17 PM

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

RBeyer 05-11-2019 03:42 PM


Originally Posted by Sean400 (Post 4685720)
It did not have a pro charger

Can you post a picture of the motor and or boat

Sean400 05-11-2019 08:05 PM

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.https://cimg0.ibsrv.net/gimg/www.off...adb5c49966.jpghttps://cimg4.ibsrv.net/gimg/www.off...1542af238d.jpg

RBeyer 05-11-2019 10:26 PM


Originally Posted by Sean400 (Post 4685693)
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?

AllDodge 05-12-2019 06:44 AM


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.

Sean400 05-12-2019 10:53 AM


Originally Posted by AllDodge (Post 4686534)
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.

got it tested with a regulator it opens at 42psi every time guess I’ll pull the regulator on the rail and test that one .


All times are GMT -5. The time now is 12:02 AM.


Copyright © 2026 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.