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Malibu sportster fuel pump issues

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Hey guys. New here and need some help troubleshooting.

I own a 1998 Malibu Sportster LX with the 310hp Indmar 5.7 carbureted. Had issues with fuel not getting to the carb. Thinking that it was the fuel pump, I put a new one on it. After putting on a the new pump it still wasn't getting fuel. Straight wired the pump to a battery and the pump would work and finally got fuel. While running with the fuel pump straight wired I checked the power wire that hooks to the bottom of the pump and it was getting 13 volts. Hooked the wires back up to the bottom of the fuel pump and it stopped feeding fuel. Any suggestions on why the pump won't work without being straight wired. Thanks in advance for any help that y'all can provide.

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Check the oil pressure sensor - I believe it will cut off power to the fuel pump if it senses no oil pressure, or if it's faulty or unhooked. Should be info here in other threads if you search.

BTW love your taste in boats! Red

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Thanks Red! 

I had read that last night about bad oil pressure sensor not supplying power to fuel pump. Which I think is weird cause it's never thrown the check engine light from low oil pressure or shown low oil pressure on the gauge. It also builds pressure on the gauge while trying to crank. Thanks for the advice.. I will start there.

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So the oil pressure sensor next to the oil filter is the possible culprit to shutting off power to the fuel pump? Can I jump the wires on the sensor to see if it fixes my issue? Then replace it if needed

What throws me for a loop is that when the pump was running off the battery I was getting 13 volts to the power wire while engine was idling. So if that sensor was bad and possibly stopping power from getting to the pump why would I still be getting a voltage read out?

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Just discussed this Wednesday. Friend swore it was a fuel pump on his 98 Sportster, but it was a ground wire towards the back of the engine.

When you turn the engine on, do you hear the fuel pump activate?

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No I sure don't. I was under the impression that a low pressure fuel pump doesn't prime like a high pressure. Thought that it just fed fuel while engine was turning over or running. 

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I would imagine that you are right. I figured you should be able to hear something too. But I never paid much attention to it until I started having this issue. Just read it somewhere on the forum that low pressure pumps don't prime like high pressure pumps. So I just figured you wouldn't be able to hear anything from it when you key-up

Edited by Strokes89
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Thanks for the clarification and link      MadMan

Jbower- Alright I will trace the ground wire back and see if it's come loose or something. Your the second person that has brought up the ground. So I'm hoping that's it. 

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1 hour ago, MadMan said:

The pump will not run at "key on", it will when you crank the engine.  Or when there is oil pressure.  This is the function of the oil pressure safety switch.



If you don't understand what MadMan is saying, the pump should get voltage when you are cranking the engine.  There is a wire from the ignition switch or from the starter motor solenoid that goes to the pump and supplies voltage even if there is no oil pressure.  The pump will get voltage under 2 circumstances: 1) You are cranking the engine during starting even if there is no oil pressure.  2) The engine is running and there is oil pressure.

You seem to having a problem with #1.  Maybe check for a loose wire or connection between the starter motor solenoid and the pump.  Or maybe a loose connection between the key switch and the pump.

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Yea I got what he was saying but thanks for going into more detail and your suggestion.

Btw yesterday I was trying to find a wiring diagram for my boat, but didn't have any luck. Anyone have one by chance or can provide me with a link?

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First check continuity between the ground terminal on the pump and another known ground.  If that is good then jump the fuel pump like you did before (but positive side only), then disconnect your jump once the engine is running.  If it continues to run normally after you disconnect the jumper then you know it is the "starting" feed that is bad.  An easy solution would then be running a wire from the starter solenoid to the pump, and not worry about the original wiring.  Kind of a ghetto fix but I don't think it'll hurt anything and will get you on the water.

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My (Clymer Indmar shop manual) wiring diagram shows any  power to the fuel pump passes thru the oil pressure switch and is supplied by the I terminal of the key switch which would be hot during cranking too .  Remember there is already gas in the carbs bowl for starting.  Oil pressure switch closes at 4-6 psi which would happen during cranking.  My diagram shows the wires on the oil pressure switch as purple wires and one should be hot with the key on.  The other goes directly to fuel pump. Hope this helps.

Edited by electricjohn
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I believe the oil pressure sensor in question is at the back of the motor near the distributor.  Pump does not run when cranking till motor starts off existing carb fuel and switch sees pressure. Last year we ran our tank dry (oops) and so also ran the carb dry. When refilled, could not start it because pump would not activate and fill the carb bowls. Had to jump power to the pump to refill the circuit, then all was back to normal. There's a way to jump the pressure switch as a diagnostic test. Will look around to find the link.

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Yesterday I checked the wires on the sensors on the back of the engine and on the sensor by the oil filter. All seemed good, just gotta figure out how to test the sensors. I also checked all wires on back of the key switch and kill switch.  I haven't pulled off the black cover where the main circuit breaker is to check behind there yet. 

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2 hours ago, minnmarker said:

 An easy solution would then be running a wire from the starter solenoid to the pump, and not worry about the original wiring.  Kind of a ghetto fix but I don't think it'll hurt anything and will get you on the water.

If I understand what you are saying, there is a problem with this.  Once the engine starts, and there is oil pressure, the power being supplied to the fuel pump will back feed to the starter solenoid and reengage the starter.

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There should be an oil pressure activated switch by the distributor. This is referred to as a fuel pump safety switch and depending on the vintage will have two or three wires. If it is a three wire switch there will be a red wire that goes to the fuel pump, a purple wire from the wiring harness and an orange wire that comes from the starter solenoid. When you are cranking the engine, the orange wire will get power from the starter solenoid (only gets power when cranking) The orange and red wires are connected together internally in the safety switch and the fuel pump should run. When the engine starts, the orange to red connection in the safety switch opens and the connection between the purple wire (always hot when the key is on) and the red wire is completed which keeps the fuel pump running. The three wire switches were somewhat problematic so we switched to a two wire switch.

With the two wire switch, the orange and red are on one terminal and the purple is on the other one. During the crank cycle, the orange wire is powered by the starter solenoid so the pump runs during cranking. When the engine starts, oil pressure closes the circuit between the purple (hot with ignition on) and the red/orange connection. The red wire supplies power to the pump and the orange wire just dead-heads at the solenoid.

Electric fuel pumps are wired this way so the pump will not run with the key on and engine off which is a Coast Guard Regulation. The see if the pump is working, you can temporarily run a jumper between the purple and red wires and turn the key on. The pump should come on. If it does, the pump is probably OK and the switch is bad. There is a three wire to two wire switch replacement kit, Indmar P/N 496007 that has everything you need to replace the three wire switch with the better two wire switch.



  • Like 3
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Wow.. Very very helpful Engine Nut. I remember checking the wires on the switch that you are referring too and mine is the three wire. Hopefully tonight I can test it by jumping the wire like you said. Thanks so much. 

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