2005 350 Mag dropping fuel pressure under load

[jrglombo]

Hey I’ve been hounding these forums but haven’t found a similar situation and have had no luck with recommendations. I have a rebuilt 2005 350 Mag MPI mercruiser with Bravo 3 drive. ECM 555 It was a repower into my older SeaRay. It starts and idles flawlessly. But under load after about a minute the fuel pressure drops from 40 to 10ish psi and the engine stumbles. It stays running after pulling back on throttle. It will consistently do this. I have no active faults on Vesselview mobile, one time I got a single beep but no record of why.

Question: if in Guardian mode, can the computer shut down fuel pump or does guardian control spark? Or how does Guardian actually shut down the engine power? Rinda scanner says I went into Guardian mode for 206 seconds, not sure why gauges read normal except water pressure gauge reads .5psi at idle 2.5 at 3000 rpm. New sensor coming to try to fix that.

New parts and things I’ve checked:
New Fuel injectors
New Cap, rotor, plugs, wires
New RW pump, circulating pump
Cleaned fuel system because it was culprit of peeling paint inside cool fuel module (I have the two pump cool fuel module)

My next steps are install water pressure sensor, Isolate twin tanks from each other, then run on a remote fuel tank. Is there a way to test voltage at the pump when underway? TIA!

 

[alldodge]

Got a motor serial number?

Guardian can happen when water pressure drops

The problem with loosing power is where I would look at fuel pressure

But under load after about a minute the fuel pressure drops from 40 to 10ish psi and the engine stumbles.

This is your current power problem

This could be a regulator issue but need more info

New Fuel injectors

Where were the injectors bought?

 

[jrglombo]

Got a motor serial number?

Guardian can happen when water pressure drops

The problem with loosing power is where I would look at fuel pressure

This is your current power problem

This could be a regulator issue but need more info


Where were the injectors bought?

Thanks! They were rebuilt Bosch on eBay. $350 for a set. There were like 400 sets sold so I was hoping they were somewhat okay. I’m figuring a pressure drop that significant isn’t an injector. Would a regulator really be able to restrict the flow that much? Does all the fuel flow through the regulator?

 

[alldodge]

Thanks! They were rebuilt Bosch on eBay. $350 for a set. There were like 400 sets sold so I was hoping they were somewhat okay. I’m figuring a pressure drop that significant isn’t an injector. Would a regulator really be able to restrict the flow that much? Does all the fuel flow through the regulator?

Was hoping you were not going to say that.
Sellers of injectors on ebay have ripped so many folks off and they keep going.

Point 1 - if an injector goes bad there is no way to rebuild it.
Think about taking something that manufactured to precise tolerances and then is crimped in stainless steel and sealed. Now to rebuild you have to cut the shell off, replace a coil driver, and reseal for less then what it cost new. This is not going to happen

Folks on ebay know full well that those buying the injectors are not going to have then flow tested to see if they react to given power inputs and deliver precise fuel amounts for given pulses.

Sorry but you got ripped off

There is an expert at Smitty's engines and transmissions that has tested a bunch of the ebay injectors on offshore only (guy I go to for injector testing) and he says most all are junk. They are injectors which failed test and sold on market for cheap to the ebayiers that resale

Point 2 - Reg will not restrict the flow, it just regulates to a specific pressure. When pressure increases above the specified value the Reg opens and sends excess pressure back to fuel filter.

Your dropping to 10 psi so something is really wrong

 

[jrglombo]

Was hoping you were not going to say that.
Sellers of injectors on ebay have ripped so many folks off and they keep going.

Point 1 - if an injector goes bad there is no way to rebuild it.
Think about taking something that manufactured to precise tolerances and then is crimped in stainless steel and sealed. Now to rebuild you have to cut the shell off, replace a coil driver, and reseal for less then what it cost new. This is not going to happen

Folks on ebay know full well that those buying the injectors are not going to have then flow tested to see if they react to given power inputs and deliver precise fuel amounts for given pulses.

Sorry but you got ripped off

There is an expert at Smitty's engines and transmissions that has tested a bunch of the ebay injectors on offshore only (guy I go to for injector testing) and he says most all are junk. They are injectors which failed test and sold on market for cheap to the ebayiers that resale

Point 2 - Reg will not restrict the flow, it just regulates to a specific pressure. When pressure increases above the specified value the Reg opens and sends excess pressure back to fuel filter.

Your dropping to 10 psi so something is really wrong

Okay I looked again and they are new Bosch, not remanufactured. Still from eBay though. Unfortunately I’m not able to pay $200-$400 each for Mercruisers injectors. I’m willing to risk a bad injector over that much difference is price. Sounds like I’ll continue to isolate the problem with a remote tank and then go from there. The plugs look good so I do not believe an injector to be dumping that much fuel if for some reason there was a bad one.

 

[Scott Danforth]

Okay I looked again and they are new Bosch, not remanufactured. Still from eBay though. Unfortunately I’m not able to pay $200-$400 each for Mercruisers injectors. I’m willing to risk a bad injector over that much difference is price. Sounds like I’ll continue to isolate the problem with a remote tank and then go from there. The plugs look good so I do not believe an injector to be dumping that much fuel if for some reason there was a bad one.

Bad injectors will cost you your motor. Have them tested

 

[jrglombo]

Alright I will get them tested, thanks. I’m still going to lose fuel pressure under load though. Hoping someone has some opinions before dismantling the fuel rail.

 

[Scott Danforth]

Have the injectors tested
Test the fuel pump
Test the anti siphon valve
Check the contents of the fuel filter

 

[alldodge]

Alright I will get them tested, thanks. I’m still going to lose fuel pressure under load though. Hoping someone has some opinions before dismantling the fuel rail.

A miracle will happen, just believe

It's not the fuel rail

 

[jrglombo]

Well I’m sure you didn’t see this coming! I took the boat out while monitoring voltage at the fuel pump. The voltage would drop to 11v each time the stalling under load occurred. Thinking I had it figured out my Vesselview mobile data would cut out also, and then the ignition beep. Ignition beep is now consistent with each stall occurrence. Is there a procedure to rule out the relay? And can anyone tell which relay is for the ecm? Next culprit is ECM? Thanks for your help here. Edit - Alternator at 14.4 volts

 

[Scott Danforth]

It's not the ECM. Check your wiring connections everywhere. Start at the battery and work your way to the helm cleaning every connection

 

[jrglombo]

Alright thanks will do. Would you agree the ECM is shutting off though? Be it wiring or anything else.

 

[Scott Danforth]

Alright thanks will do. Would you agree the ECM is shutting off though? Be it wiring or anything else.

If your voltage feed to the ECM drops below 9volts yes.

So find out where the bad connections are

 

[jrglombo]

I will add that I connected to Vesselview mobile on my phone with the engine running and it stalled the engine.

 

[alldodge]

Bad connection somewhere
The relays are Main power and other is fuel pump. Main powers up entire motor and both are same kind and can be swapped.

 

[kenny nunez]

Bravo drives especially as yours is older are known to cause low water pressure. You stated that you were going to test it. That could be the whole problem. If it is, the best thing to do is to go through the hull bottom for incoming water connecting the drive’s water to the hull supplied incoming with a “Y” arrangement.

 

[jrglombo]

Bravo drives especially as yours is older are known to cause low water pressure. You stated that you were going to test it. That could be the whole problem. If it is, the best thing to do is to go through the hull bottom for incoming water connecting the drive’s water to the hull supplied incoming with a “Y” arrangement.

That’s a good tip. So it can pull water from a seacock and also the existing supply?

However would low water pressure shut the computer off completely?

 

[kenny nunez]

I believe that is one of the Guardian modes. I might be wrong but it is worth a try. There also are kits that put the water intake on the transom so you do not have to go through the bottom.
And yes you want both water supplies merged before the pump.
I once had a Donizi with the 555 system and I hooked it up with the dual intake system. Your boat should have a water pressure gauge on the instrument panel.

 

[jrglombo]

Well I’m just full of problems I guess. I replaced the water pressure sensor and it reads correctly now. Score. Also I replaced the relay for computer because it was cheap enough.

I was out for a much longer test ride this time testing at all different levels of rpm. Thought I was good after 15-20 minutes so headed in but fuel pressure dropped again. This time I verified with voltmeter that the voltage to pump does not lower. The pressure recovers so quickly when you pull back the throttle. I feel like maybe the low pressure pump isn’t feeding the hi pressure pump enough when this happens. Isolating between the two tanks doesn’t change the instance. Verified my pickups are good. Boat is old enough not to have antisiphon valves. Fuel water separator is fuel when removing

 

[jrglombo]

Update here. There was a 1/4” drill socket used to plug the line during repower stuck in the line. I’d call that a fuel restriction LOL. I’m going to test tomorrow as the north wind was howling today on Lake Huron, gotta think that was the problem. No idea if I or a helper shoved the line on with that fitting still in there. Ridiculous!