1998 7.4L High Fuel Pressure 60psi

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rjpjr924

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Jun 7, 2007
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I am haveing a problem with one engine on a twin setup. The engine will start and run for about 15 seconds, then surge and stall.

The background on engine 1998 7.4L MPI:
Serial Number:
0L004110 (Inboard V-Drive)
0L004113 (Inboard V-Drive)
Brand new long block, fuel injectors and exhaust manifolds. All other components switched from original engine.
Did the install right before winter so did not perform sea trial, but ran in boat fine and then winterized last season.
Went to decommission this spring and now have the situation of high fuel pressure of 60 psi.

Diagnostics done so far:
Check for codes - none
Ran on remote fuel tank with new Fuel/Water separator - made no difference.
Swapped fuel pressure regulator from other working engine (the one at the fuel pump /cooler) - made no difference.
Swapped fuel injectors from other working engine - made no difference.

My questions is will a fuel pump fail and be able to put out that much pressure or could there be a restriction?

The only parts after the pump are a fuel line and what looks like to be another regulator, rail and injectors. Is that regulator serviceable or part of the rail system?

Any input would be greatly appreciated.
 
Last edited:
alldodge

alldodge

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Messages
42,572
Re: 1998 7.4L High Fuel Pressure 60psi

rjpjr924 said:
I am haveing a problem with one engine on a twin setup. The engine will start and run for about 15 seconds, then surge and stall.
The background on engine 1998 7.4L:
Serial Number:
0L004110 (Inboard V-Drive)
0L004113 (Inboard V-Drive)
Brand new long block, fuel injectors and exhaust manifolds. All other components switched from original engine.
Did the install right before winter so did not perform sea trial, but ran in boat fine and then winterized last season.
Went to decommission this spring and now have the situation of high fuel pressure of 60 psi.

Diagnostics done so far:
Check for codes - none
Ran on remote fuel tank with new Fuel/Water separator - made no difference.
Swapped fuel pressure regulator from other working engine (the one at the fuel pump /cooler) - made no difference.
Swapped fuel injectors from other working engine - made no difference.

My questions is will a fuel pump fail and be able to put out that much pressure or could there be a restriction?

The only parts after the pump are a fuel line and what looks like to be another regulator, rail and injectors. Is that regulator serviceable or part of the rail system?

Any input would be greatly appreciated.
Click to expand...

There is nothing wrong with your pump if your seeing 60PSI. If it stays there even while it's running for the 15 seconds then check to see if your vacuum line is connected between the intake plenium and the fuel pump diaphram.

The surge and stall my first guess wuold be your IAC. Can you keep it running if you use some increased throttle? If you can keep it running it's probably your IAC, even if you cannot, I suggest remove and clean it.
 
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rjpjr924

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Joined
Jun 7, 2007
Messages
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Re: 1998 7.4L High Fuel Pressure 60psi

Vacuum line is connected. I can keep it running when I increase the throttle but It still surges and the pressure will increase from 60 to about 75. If I try to return to idle and it will stall. I did not want to run it that long incase it will damage anything.

I swapped IAC from other working engine - made no difference.
 
alldodge

alldodge

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Re: 1998 7.4L High Fuel Pressure 60psi

rjpjr924 said:
Vacuum line is connected. I can keep it running when I increase the throttle but It still surges and the pressure will increase from 60 to about 75. If I try to return to idle and it will stall. I did not want to run it that long incase it will damage anything.

I swapped IAC from other working engine - made no difference.
Click to expand...

Do you know what kind of vacuum your pulling when it's running? With running that high a pressure either I'm leaning toward a vacuum leak, bad diaphram, maybe a MAP sensor. Good thing with twins you can swap parts. Do you have access to a code reader?

Side note: been helping out my buddy fix his 99 7.4 MPI horizon (twins) in his boat, but didn't have your issue
 
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rjpjr924

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Messages
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Re: 1998 7.4L High Fuel Pressure 60psi

No I did not check for vacuum I will check to night.
I also swapped MAP, Throttle Valve Body with TSP and IAC and then Upper Plenum from other working engine - made no difference.
Yes I have DIACOM Marine PC software.
What do mean by a bad diaphragm?
 
alldodge

alldodge

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Staff member
Joined
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Messages
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Re: 1998 7.4L High Fuel Pressure 60psi

rjpjr924 said:
No I did not check for vacuum I will check to night.
I also swapped MAP, Throttle Valve Body with TSP and IAC and then Upper Plenum from other working engine - made no difference.
Yes I have DIACOM Marine PC software.
What do mean by a bad diaphragm?
Click to expand...

Good more info, swapped all that stuff and no help. The diaphragm I'm referring to is in the fuel pressure regulator (I should have just said fuel regulator). Pull vacuum line off regulator and see if there is fuel in it.

Next thing if you see no codes is to do a compression test, I know new engine
 
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rjpjr924

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Jun 7, 2007
Messages
9
Re: 1998 7.4L High Fuel Pressure 60psi

There is no sign of fuel in vacuum hose at regulators.
It is a MPI.
I will do a compression tomorrow.
 
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