Mercury 3 liter EFI experts???

[rdoaner]

I recently purchased a Merc 3l EFI "Offshore series" from 1996 I want to say. The oil injection was disconnected when we got it, and the mechanic had significant trouble getting the oil alarm to turn off without disabling all warning alarms (but eventually got it figured out).

Upon testing, the boat popped the boat (a 23 SeaCraft) onto a plane a couple times, but other times bogged down and couldn't get her on a plane. The diaphragm pump has been replaced as well as spark plugs, and still same issue. The mechanics are scratching their heads and have basically given up. They think that once you disable the oil injection on this motor, it screws with the computers, leading to our symptoms.

Are there any experts on this particular motor that could give input? Even better would be someone willing to drive to the Palm Beaches in Florida to take a look at it (and get paid of course!)

[vnemous]

Removal of oil injection has no effect on motor, that is as long as you are now premixing your oil. I've run my 1998 250 efi like this for years. The symptoms you have are the same as when one of the bobbins on stator starts to go. JMO

[rdoaner]

Removal of oil injection has no effect on motor, that is as long as you are now premixing your oil. I've run my 1998 250 efi like this for years. The symptoms you have are the same as when one of the bobbins on stator starts to go. JMO

Thanks for the reply! As a quick update, I just test-rode the boat myself for the first time. It seemed to me that the exhaust was only coming out of the hub, making the engine sound really quiet and anemic at lower speeds. When we tilted the motor up before gunning it, it finally planed out. No water/splash got anywhere near the powerhead (no matter how it was trimmed), so I have a theory that perhaps the exhaust is being pushed underwater causing enough back pressure to bog the engine down. I'm thinking when we tilted it up, it raised the exhaust enough such that it it could start planing, where speeds are fast enough to create a low pressure area behind the prop. Is this possible? Or do you think this was just a coincidence?

Edit: I'll add it's a 30" shaft, so that prop is REALLY deep in the water

[half fast]

Try a prop with less pitch. hf...

[rdoaner]

Try a prop with less pitch. hf...

It's not that, it jumps on a plane when we're not having the issue, it's propped perfectly as per Ken's recommendation at PropGods, and it's a SeaCraft, which is a famously easy hull to put on a plane

[lpugh]

What prop is on there and how is it vented
What are the wot rpms when the trim is set maximum speeds
You need to find a mo better Mercury technician

[Merc 2.5]

It's not that, it jumps on a plane when we're not having the issue, it's propped perfectly as per Ken's recommendation at PropGods, and it's a SeaCraft, which is a famously easy hull to put on a plane

Every boat is diffrent even the same 2 hulls. U cant take 1 person word for it and think u cant get any better setup cause that person said , your prop needs more ventilation or u need go down little in pitch. What r the wot rpm and mph and what pitch prop now?? Will b very helpful to know those #s

[vnemous]

The prop isnt sometimes gonna get you on plane and sometimes not. If its a prop issue it might need to be ventilated. But if its a symptom that comes and goes you're looking in the wrong place I bet. JMO

[lpugh]

be be sure it is vented to achieve 3500 pulse rpm during hole shot.Pull the power head and clean the idle relief ports
Removing oil injection will cause a lot more carbon to form in the relief holes as well as ring grooves, I am not a fan of removal on fishing motors, I get it on race motors though

[rdoaner]

The prop isnt sometimes gonna get you on plane and sometimes not. If its a prop issue it might need to be ventilated. But if its a symptom that comes and goes you're looking in the wrong place I bet. JMO

Agreed, and thank you! Btw do clogged idle relief ports affect the motors performance? Cause they are most certainly clogged

[rdoaner]

Thought I'd give an update:

When the boat was finally delivered, I took off the cowling and noticed one of the spark plug wires was severed (my mechanics must've been blind?). On top of that, the throttle was mounted in such a way that it runs into the console before reaching full throttle. That combination is one that would make it difficult to plane a boat.

Well, two weeks ago I got the motor to Chaz, who not only knows his sh!t but really takes pride in his work. He has quite an impressive shop, as well as quite impressive attention to detail. He will be doing a complete restoration of the motor, as well as replacing the reed valves, drilling out the exhaust tube, and presumably sprinkling some of his magic into the motor.

When I talked with Chaz, he seemed interested in documenting the process for ScreamandFly (I hope I got that right Chaz... if not my apologies!). If so I know I will not be the only one interested in seeing the process

When she's all said and done, I will be updating with a video of her performing. Very excited to show this motor off... the 1995-1999 Merc Offshore EFI 3 liters are my favorite motors of all time