7.4 mpi doesn’t want to idle?

Joined
Jul 2, 2021
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6
I have a problem with my 7.4 mpi... it just doesn’t want to idle. I did clean out my tank lines and injectors replaced the tps, iac, rotor cap plugs wires cleaned up some corrosion. New batteries new fuel pressure regulator. Not sure if the pump needs replaced yet. Also new temp sensor...Thank you...
 

alldodge

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Is this a new to you boat, or a new problem?

What is your motor serial number?

What is the fuel pressure at the rail?
 

CayugaCobalt

Petty Officer 2nd Class
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May 6, 2008
Messages
138
Can you define the problem in more detail? Problem is only in neutral? It always starts easy? Runs good at all speeds?

Alldodge: I have heard the spec on fuel pressure is 8 to 62 psi. Is that accurate. Does one get 8 psi at idle and 62 psi at WOT?
 
Joined
Jul 2, 2021
Messages
6
Is this a new to you boat, or a new problem?

What is your motor serial number?

What is the fuel pressure at the rail?
Not a new boat, a salvaged boat 2001 cobalt 232
i have 43 psi constant.
serial # 0M006877

i have had the boat for a couple of years. Not a new problem, i've been trying to solve it for a while now. It was salt water boat. the fuel system was REALLY dirty. it had lots of stuff in it from sitting for at least a couple of years. I cleaned it all tank, lines replaced fuel water separator with a large 10 micron filter to catch anything i may have missed in the tank. replace all 8 injectors. I just cant get it to idle i give it some throttle it will keep running. anything above 1000 RPMs is great. load or no load it runs but under 1000 rpm it surges and wants to quit. i cant get any help locally because the boat was in salt water they will only work on fresh water boats.
 
Joined
Jul 2, 2021
Messages
6
Can you define the problem in more detail? Problem is only in neutral? It always starts easy? Runs good at all speeds?

Alldodge: I have heard the spec on fuel pressure is 8 to 62 psi. Is that accurate. Does one get 8 psi at idle and 62 psi at WOT?
its 43 psi constant, idle, WOT its 43 PSI. load no load 43 psi. the problem is under 1000 rpms,. dosnt matter neutral, forward, reverse. it wants to quit / surge and quit.
it always fires right up i have be fast on the shifter to get into gear and give it gas when i start it. better when cold but when its warm its really hard to keep it from stalling once it goes under 1000 rpm. it has the cool fuel 2 system
 
Joined
Jul 2, 2021
Messages
6
its 43 psi constant, idle, WOT its 43 PSI. load no load 43 psi. the problem is under 1000 rpms,. dosnt matter neutral, forward, reverse. it wants to quit / surge and quit.
it always fires right up i have be fast on the shifter to get into gear and give it gas when i start it. better when cold but when its warm its really hard to keep it from stalling once it goes under 1000 rpm. it has the cool fuel 2 system
when it has warmed up it will fire right up and quit. i can put my hand on the the engine and its not crazy hot, also put a new sea pump in it.
 
Joined
Jul 2, 2021
Messages
6
its 43 psi constant, idle, WOT its 43 PSI. load no load 43 psi. the problem is under 1000 rpms,. dosnt matter neutral, forward, reverse. it wants to quit / surge and quit.
it always fires right up i have be fast on the shifter to get into gear and give it gas when i start it. better when cold but when its warm its really hard to keep it from stalling once it goes under 1000 rpm. it has the cool fuel 2 system
Also replaced the iac
 

alldodge

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Mar 8, 2009
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43,239
Pressure is good
Connect a vacuum gauge up to the intake, probably the line that connects to the fuel pressure regulator.

Need a scanner to see what the MAP and IAC are seeing.
Could measure voltage of the 2 but a scanner would be better
 
Joined
Jul 2, 2021
Messages
6
Pressure is good
Connect a vacuum gauge up to the intake, probably the line that connects to the fuel pressure regulator.

Need a scanner to see what the MAP and IAC are seeing.
Could measure voltage of the 2 but a scanner would be better
I’m thinking the problem mite be a dirty injector. A cylinder was cutting in and out when we were out yesterday.
 
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