fuel pump not running

jimking

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Jun 27, 2012
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I have a 2002 chaparral 183ss with a Mercruiser 4.3 Alpha1 carburated motor. I recently purchased this boat a month ago, and upon the test drive before me buying it the boat and motor ran perfectly. the seller said that they had not changed the oil in the motor this season yet, and that I should do that before taking it out. so a week later when changing the oil the motor ran fine while i was warming the oil up so that it could be changed. Two days later on Saturday morning I took the boat out for my first time on the water. It would not run! 45 minutes went by of me trying to get it to run and it just wouldn't. upon bringing the boat back home, and checking things and testing things, I found out that the electric fuel pump was not running. so I made some jumper wires and jumped the pump directly to the battery and the pump runs fine, it just doesn't run at all when plugged into the factory wiring harness. I have looked through the service manuel to see if there is some kind of fuse that's tied to the fuel pump and I cannot find anything of the such. upon searching throughout the boat for a fuse panel or fuse blocks there is nothing to be found as well. the only thing that I have is a black relay box under the driver's console, and none of those relays have anything to do with the fuel pump. so meanwhile I went ahead and hooked up a temporary toggle switch with a fuse block from the battery directly to the pump so that I could use the boat and it runs perfectly. also everything else on the boat works in perfect condition. all my gauges work, trim, battery, oil pressure, water temp, spedo, and tach, etc. so I am just mind boggled on why the fuel pump worked fine on thursday when changing the oil, and then come saturday it doesnt. please someone help me with this because the miss's is a little disturbed. also, i believe you should hear the fuel pump start pumping when you turn the key to the on position, we don't even hear that.
 

spdracr39

Lieutenant Junior Grade
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Aug 30, 2010
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1,238
Re: fuel pump not running

You almost definitely have a fuel pump relay that controls that pump. Again it is usually on top of the engine near the main circuit breaker. Trace the wires by color from the fuel pump back to its power source and you will find it. Even if you don't have a relay you will have to find where the pump is getting its power from to find the problem.
 

Don S

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Re: fuel pump not running

You do not have a relay on your carbed engine, so don't go looking for one.

You do however have an oil pressure switch that controls the fuel pump. It's located on the port side of the engine just above the oil filter. Sounds like you may have knocked the wires off of it while changing the filter.
 

mikeheron

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Mar 17, 2012
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Re: fuel pump not running

it happend to me to check your wires to the switch if its not unpluggged you may need a oil pressure switch. i did a simple test jump the 2 wires going to the switch, turn the key on if the pump runs replace the switch. hope this helps
 

jimking

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Jun 27, 2012
Messages
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Re: fuel pump not running

you make a good valid point on me possibly knocking the wire off the oil pressure switch. I did have a hard time getting that oil filter off when changing it and may have gotten pulled off. I will check that later today and let you know. thanks a bunch. but if that wire is still connected, what also could possibly be the problem?
 

Failproof

Petty Officer 1st Class
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Sep 26, 2011
Messages
273
Re: fuel pump not running

The pump will not run unless its wired wrong, with the KOEO. It should only run when engine is running, and if KOEO directly after engine shut down whilst oil pressure exists in the system.
 

Don S

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Re: fuel pump not running

and if KOEO directly after engine shut down whilst oil pressure exists in the system.

Won't run then either, when you shut the key off, you shut the power off TO the pressure switch which is the purple wire. Same one used for the ignition.
 

Failproof

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Re: fuel pump not running

Won't run then either, when you shut the key off, you shut the power off TO the pressure switch which is the purple wire. Same one used for the ignition.
Sorry, KOEO directly means KEY ON, ENGINE OFF.
 

jimking

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Jun 27, 2012
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Re: fuel pump not running

so, if I discover that the pressure switch has been accidentally unplugged and I plug it back up and it fixes the problem, should I hear the fuel pump run or prime or anything when turning the key to the on position before cranking the motor up?
 

Don S

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Re: fuel pump not running

Sorry, KOEO directly means KEY ON, ENGINE OFF.

How do you shut the engine off with the key ON ?????

KOEO could also mean Key Off Engine Off, or Key On Engine On, or maybe Key On Engine Off.. :facepalm:
 

Failproof

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Re: fuel pump not running

No, pump will not run unless oil pressure above set is reached, or during cranking. If you can hear it when cranking, but not when engine is running it could be a switch. Then you would pull connector off switch, bypass switch with jumper, then turn KOEO. If pump still does not run, then suspect wiring/fuse.
 

Don S

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Re: fuel pump not running

so, if I discover that the pressure switch has been accidentally unplugged and I plug it back up and it fixes the problem, should I hear the fuel pump run or prime or anything when turning the key to the on position before cranking the motor up?

Nope, the pump will not get power until you start cranking the engine over. The fuel pump gets powered up from the starter solenoid when starting.

Fuel Pump Wiring.jpg
 

jimking

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Jun 27, 2012
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Re: fuel pump not running

so help me out on some clarifications, I don't want to sound like an idiot of anything but the fuel pump will continue to run the whole time while the motor is running correct?
 

Failproof

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Re: fuel pump not running

How do you shut the engine off with the key ON ?????
KOEO could also mean Key Off Engine Off, or Key On Engine On, or maybe Key On Engine Off.. :facepalm:
You turn the key off. Engine dies. You turn the key back on!!!! If you do it fast, oil pressure is still above set point, fuel pump still runs, and badda boom the oil pressure drops, pump shuts off. Diagnostic done. The wiring is good. The switch is good. Done.

KOEO has been key on engine off and KOER has been key on engine running since they started writing service manuals. Auto, heavy equip, and aero use it. A few of my marine use it. Makes sense yes? Much easier than telling someone to "turn the key to the run position but do not start the engine, then perform the test" you say with KOEO perform following test
 

jimking

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Jun 27, 2012
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Re: fuel pump not running

also, what could be a possible reason why my electronic choke to not work?
 

Failproof

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Re: fuel pump not running

Yes pump should run while engine runs. If both your electric choke and your fuel pump are non-op, are you getting power at coil?
 

Don S

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Re: fuel pump not running

also, what could be a possible reason why my electronic choke to not work?

If it has voltage to it, and a good ground, then the choke coil probably failed.
 

jimking

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Jun 27, 2012
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Re: fuel pump not running

so the choke coil would be the black round thing on the side of the carb correct?
 
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