Bad Pressure Regulator?

Thomv

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Feb 26, 2005
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On one of my 1998 454 MPI engines, when I hook up a fuel pressure gauge, I get a reading of about 30 PSI with the ignition switch on. Once I start the engine my pressure gauge goes all the way up 70 PSI and rapidly fluctuates between 70 and 80 PSI. When I shut off this engine the pressure goes back down to 30 PSI. Do I have a bad regulator?
 

achris

More fish than mountain goat
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May 19, 2004
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27,468
How does it perform on the other engine?

Check the vacuum line from the back side of the regulator to the plenum and the rail regulator. If that's blocked or disconnected, it will influence the regulator.

EDIT: Just been going through the service manual and the parts diagram for your engine. You have 2 regulators on that engine. One on the fuel pump itself and the other on the injector rail.
 
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Thomv

Petty Officer 1st Class
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Feb 26, 2005
Messages
244
How does it perform on the other engine?

Check the vacuum line from the back side of the regulator to the plenum and the rail regulator. If that's blocked or disconnected, it will influence the regulator.

EDIT: Just been going through the service manual and the parts diagram for your engine. You have 2 regulators on that engine. One on the fuel pump itself and the other on the injector rail.

On my other engine, once I turn on the key, my fuel pressure gauge shows about 35 PSI, Once the engine is started, it remains very steady at 35 PSI. Totally different then the other engine's readings, while the engine is running. I will check the vacuum line. I believe you are correct that I have two fuel regulators on both engines.
 

Fun Times

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Well you know the fule pumps working because it has the capability of producing high fuel pressure so most times when you have high pressure like that you tend to have a clogged screen under the fuel regulator item number 16, http://www.mercruiserparts.com/Show...2705&bnbr=110&bdesc=FUEL+PUMP+AND+FUEL+COOLER or the regulator next to the fuel pump is actually defective. While your down there, you may as well do both even if you find the screen dirty.

Also check and change the fuel filter and it wouldn't be a bad idea to blow some air between the fuel return hose of the regulator and the fuel filter assembly in case there's some debris in the line as a clogged fuel return line causes high pressure.

Luckily the regulator on/at the end of injector rail is used more as an fuel damper vs regulator like mentioned in the in the parts catalog. Why do I say lucky you ask? $$$,:watermelon: Let us know what you find, good luck.:)
8M0069803REGULATOR-FUEL802630T$391.92$353.32$0.00$0.000.32 Lbs
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Thomv

Petty Officer 1st Class
Joined
Feb 26, 2005
Messages
244
Well you know the fule pumps working because it has the capability of producing high fuel pressure so most times when you have high pressure like that you tend to have a clogged screen under the fuel regulator item number 16, http://www.mercruiserparts.com/Show...2705&bnbr=110&bdesc=FUEL+PUMP+AND+FUEL+COOLER or the regulator next to the fuel pump is actually defective. While your down there, you may as well do both even if you find the screen dirty.

Also check and change the fuel filter and it wouldn't be a bad idea to blow some air between the fuel return hose of the regulator and the fuel filter assembly in case there's some debris in the line as a clogged fuel return line causes high pressure.

Luckily the regulator on/at the end of injector rail is used more as an fuel damper vs regulator like mentioned in the in the parts catalog. Why do I say lucky you ask? $$$,:watermelon: Let us know what you find, good luck.:)
8M0069803REGULATOR-FUEL802630T$391.92$353.32$0.00$0.000.32 Lbs
Part Number Description Superceded
From
List
Price
Online
Price
Core
Chg
Cont
Chg
Ship
Weight
Each
Order
Quan

Hopefully this Saturday I will be attempting to check, both the fuel return hose and bother regulators. Before spending several hundred dollars on a replacement regulator, besides blowing out the fuel return hose for a possible blockage, is there a way to test the actual regulator to see if that is the culprit. I would hate to put out the dollars for that replacement only to find out the one I replaced was fine. In the past I have done that. It also looks like I will need to remove both risers and exhaust manifolds between both engines to get access to the fuel regulator. I don't look forward to that along with the expense of having to replace both gaskets on both engines. I have never owned a boat where a boat company would try and place both starboard and port engines so close together that it is virtually impossible to access anything below the intake manifolds. Very frustrating to say the least!
 

Thomv

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Feb 26, 2005
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After about three hours I was able to remove the fuel pressure regulator. I had very little room to work getting to it. Just taking off the Mercruiser black insulator cover was very difficult because it was right up against my motor mount bracket. I was not able to pry out the little screen filter below the fuel pressure regulator. I did place an order for the regulator and screen filter along with replacements for the knock sensor and oil pressure sensor which both were badly rusted. I was surprised the knock sensor cost over $100! The vacumn line had no blockage.Hopefully this will solve the high erratic pressures
 

Thomv

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Feb 26, 2005
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This weekend I will be installing the new pressure regulator. Can I start my motor without first installing my exhaust manifold and riser? The reason why I would like to do this is make sure, once my motor is running I don't still experience the high 70 to 80 PSI that only happened when the engine was running. With the engine not running my pressure was around 38 PSI when I turned on the ignition key. I don't want to go through the hassle of installing both the manifold and riser onty to have to take them off one more time to find what is causing my high running pressure. The vacumn line did not have any blockage and I will also be replacing the small filter screen mounted to my fuel pump.
 

Thomv

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Feb 26, 2005
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Just finished up on the installation of a new OEM fuel pressure regulator. What a nightmare accessing it on the cool fuel MerCruiser System. Now when I turn on the ignition key my pressure is around 39 PSI. When I start my engine the pressure gauge no longer jumps up and bounces between 70 and 80 PSI. It now stays steady at around 38 PSI just like my other engine. One of the problems accessing this regulator is the fact that the whole assembly is at the bottom of the engine sandwiched between my other engine making it very difficult to access. I still have two mote issues I need to tackle but that is for another day.
 

Fun Times

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Good to hear that all of the hard work you're doing is paying off.:thumb: How did the little screen look?
 

Thomv

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Feb 26, 2005
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244
Good to hear that all of the hard work you're doing is paying off.:thumb: How did the little screen look?

The little screen that I replaced looked okay. Because I already purchased a new one I went ahead and installed it.
 
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