350 Mag fuel pump cuts off intermittently

[Mhill3784]

2006 Searay 220 select with 350 Mag
while under power the engine will cut off randomly but always fire back up. I installed a fuel pressure gauge and found that the fuel pump actually (audibly) cuts off and fuel pressure drops to zero. Sometimes it will die completely other times the pump with cut back on and engine run fine until it happens again.
I have a Mercruiser computer and no codes are present except for a random fuel pump relay ck code a week ago in which I changed the relay on the water and it did not fix. Lately it has taken atleast 45 min of riding to duplicate the engine cutting off at speed. I have not checked for 12 volts at the fuel pump when it does die.....with the information given does it sound like a failing fuel pump or do I need to check for voltage when it does die? I have a video of the pressure gauge if someone can tell me how to post it.

 

[alldodge]

Have a serial number?

 

[Mhill3784]

Ow338961

 

[alldodge]

I'm thinking a bad connection, either on the Green wire between Pin A19 and Relay pin 86, or the fuel pump ground (not shown in pic). Could also be a bad connection on the hot side, but would start with ground on fuel pump first

 

[Mhill3784]

Is the green wire from ecm connector to the relay a hot or ground? Where does the fuel pump ground to?

 

[Mhill3784]

For what it’s worth, I don’t believe I was able to feel the relay click when the fuel pump stopped pumping. But could have just been too much motor vibration to feel it.

 

[Mhill3784]

[No message]

 

[alldodge]

The green wire is a ground, and the ECM applies a ground to energize the relay. The ground on the fuel pump should be a black wire coming straight off the pump along with the red from the pump. After the pump connector it should go into the harness which connects to other grounds and then is attached to the block.

Pull the connectors and have a look at the contacts, this includes the ones on the relay connector, make sure they fit clean and tight

 

[alldodge]

Now that is just flat different. Your saying the motor continues to run while the pressure is dropping, or this is the key ON but motor not running?

 

[Mhill3784]

In the video the motor continues to run while fuel pump cuts off and then cuts itself back on and stays running. In other instances at WOT when the pump cuts off it has completely died on me. Turn the key off, turn key back on, let the pump prime and cranks just fine. The video was taken after it tried to die on me and I quickly jumped to the back while in idle to get that video...

 

[Mhill3784]

If you watch the video with sound you’ll hear the motor running and also you can hear the pump cut back on as the pressure rises. Meaning while the pressure is dropping the pump is audibly NOT on...

 

[alldodge]

What gets me is how the motor continues to run with the pressure that low. If it was a carb motor I would understand, but fuel injectors need more pressure.

Need to check your connectors, disconnect the battery and then pull the ECM plugs arn look for anything that isn't clean

 

[Mhill3784]

I just pulled the ECM plug and checked #19. Exceptionally clean and the wire does not appear to be loose. Then moved to the Relay and checked all connections, tugged on green wire and seems tight, also the tabs that connect to the relay are not bent and make a tight connection. Would it be a good idea to try conductive grease in those 2 connections? I have had an instance where it took 2-3 key turns for the relay to click and engage the pump.

 

[alldodge]

Not sure dielectric grease would be a good idea. When you turn then key to ON, do you hear a short beep?

Hey muc this is a strange one for sure

 

[Mhill3784]

Yeh short beep. Wait for pump to prime and then it cranks just fine. After it dies...every now and then it will take 2-3 key turns with beeps to hear the relay click and pump to prime.

 

[alldodge]

The beep is good, means the main power relay has energized the ECM and it came back with all is good, but the relay is not coming ON, so I'm now thinking more a ECM issue. Still doesn't explain how it will run with next to no pressure, maybe muc of Fun Times may have a clue

 

[Mhill3784]

Would the oil pressure sensor be after the Relay or before? Or is that even in question

 

[alldodge]

Oil pressure sensor/switch has no connection with your fuel pump

 

[Mhill3784]

What tells the fuel pump to shut off when you turn the key but do not start the engine?

 

[alldodge]

What tells the fuel pump to shut off when you turn the key but do not start the engine?

The ECM
Key turns, ECM checks things says all is good, primes fuel by turning pump on for couple seconds. Once the motor is cranking, the ECM looks to see that the distributor is firing and then turns fuel pump back on (all done real quick)