Fuel pump on 2000 225 efi

[hawksuper1900]

Buddy has a boat that is real boggy coming out of hole. We started checking different things. When we got to fuel pump checking across the post on fuel pump we get 11.70 volts with key on. When we fire it up goes to 13.57 volts and after few seconds it drops to 10.50 volts. I would think it should stay above 12 volts. Any ideals. I'm thinking either fuel pump is bad or the ecu is telling it to drop

2000 225LEFI
Serial # 0T076321


Fuel pressure was at 32 psi also.

[lpugh]

what is the voltage at the battery when the pump is at low voltage
What is voltage from negative battery to fuel pump positive
What is voltage from negative battery to fuel pump negative

[hawksuper1900]

While it was running and fuel pump check 10.50 the voltage coming out of positive wire on alternator it was 13.5 volts. We checked the fuel pump from a ground on the motor on bolt - and + post. It checked 12.70 on + and 12.70 on - post on fuel pump .. anything else we can check.

[lpugh]

While it was running and fuel pump check 10.50 the voltage coming out of positive wire on alternator it was 13.5 volts. We checked the fuel pump from a ground on the motor on bolt - and + post. It checked 12.70 on + and 12.70 on - post on fuel pump .. anything else we can check.

Fuel pump can not operate with 12.7 on the negative side of the pump, was this with engine not running? Voltage on - side running should be less than 1 volt, Positive should be within 1 volt of the battery
Voltage across the pump + to - should be almost the same as source voltage, less than 1 volt
Use battery negative for testing, ground level voltages at other locations may vary even though they should not
Be sure the gauge is dead on accurate, check tire pressure with it and compare, I think your motor requires 34 to 36 psi, If you have 12 volts across the pump running, I doubt you have a concern on the electrical side or computer as far as fuel pump operation is concerned

[hawksuper1900]

OK here what we got

Motor not running
On both + and - post on the fuel pump it checks around 12 volts

Motor running

When we first start the engine we have around 13 volts on + side but after about 3 to 4 seconds the voltage will drop to 10.50 on the positive side

This we have tried

We ran a ground wire to fuel pump - side post. Of course it kicks pump on. But we will fire it up and while it is running with negative to battery the voltage is around 13 volts.

So we thought the ecu was bad so we run the ground with back to the ecu from the battery. Thinking maybe it had a bad ground at ecu. We still got same results we got 10.5 volts on the + side of fuel pump.

So we found another ecu off another motor. We was thinking ecu was bad tried it with the other ecu and still after a few second it goes from 13 volts to 10.5 volts.

We got 32 psi pressure coming out of regulator. Not sure if the gauge is dead nuts accurate. When we rev motor up the pressure does not drop.

What were seeing is that the pump is suppose to drop to 10.5 psi. After putting to different eciu on it and still does the same. I guess the ecu tells it to drop. Which still makes no sense to me.

[hawksuper1900]

Sorry bought the 3 post.

[lpugh]

ECU does not control the voltage to the pump, it controls ground level voltage, some systems do vary the ground side a little. If positive side is dropping there as a resistance somewhere in that circuit. I would first to the fuel pump fuse and verify it has a good connection, discoloring or voltage drop across it

[EuropeanAM]

ECU modulates the GROUND for the fuel pump, so voltage across the terminals (or on the ground side) will vary.

If you have, and are maintaining 32 psi fuel pressure, I suspect you're down a rabbit-hole and there may not be a problem (or rabbit) there.

[hawksuper1900]

Well to start off by say we have caught the rabbit in the hole

Here what we did. The fuel pump dropping down to 10.5 was just killing me. So we did the toggle switch effect. We took the negative wire off of the fuel pump that goes to the ecu. Run unless a ground wire from battery to to ground on fuel pump and added a toggle switch so could controll it and not burn pump up. When we did this we was getting 35 psi of fuel pressure.

So off to centerhill lake we went again. Turn toggle switch on and started motor. Sounded smoother. Trim the jack plate and motor alway down. Then wot. She jumped out of hole like a completely different motor. Buddy that owns the boat got on front deck and did happy dance. Lol

So next thing we got to do is find out what is causing the fuel pump drop down to 10.5 volts. We have tried a different ecu so any one have a ideal were i cant start.

What is old is it will do 13.5 volts when you first start it for about 3 to 5 seconds. So what is tied into the ecu that might be kicking on. Any ideals are needed

[Savage]

I would be cleaning the PCM grounds and all the other grounds where they touch the aluminum block.

[EuropeanAM]

Try this:

Add two (2) 10ga grounds to the Electrical Plate at the back of the engine.

-One connected to the STB-TOP ground point, running up over the block and connected to the battery cable GROUND bolt.

-One connected to the lower ECU, on the same bolt that currently has a ground wire (run this one under the head/block and then up to the battery cable ground bolt).

Sometimes the harness crimps for the grounds begin to fail- and this will almost always resolve it if that is the case.

[hawksuper1900]

We have put new 4 gauge ground from battery to motor. We have also cleaned all grounds on motor. Plus added the 2 grounds and it still goes down to 10.5 when wired up correctly. But if we added straight ground from battery it runs at 14.5 volts which is what coming out of alternator. Now what

[Savage]

We have put new 4 gauge ground from battery to motor. We have also cleaned all grounds on motor. Plus added the 2 grounds and it still goes down to 10.5 when wired up correctly. But if we added straight ground from battery it runs at 14.5 volts which is what coming out of alternator. Now what

Your "work around" proves that a ground wire somewhere on the motor is not good. The ground wire(s) could be bad internally.

[EuropeanAM]

+1... OR the Fuel ECU has a poor connection (or an internal failure in the driver circuit).