350 MPI suddenly Cut Out at 3700 rpm.

[SeaAyeOwe]

So, I have not started the fault finding yet because of a prior commitment but thought I would ask the forum for advice.

Half tank of fresh fuel from two weeks ago, new distributor cap, plugs and leads 25 hours ago.

I got up on plane with 4 adults and child, an hour after engine started, at 3700 rpm or so my port engine suddenly died. No alarms visible on smart craft other than Port Lo Speed.

Dropped anchor, opened hatch, nothing is visible at all - I was hoping it was a fan belt failure. No fuel smell, nothing visible electrical failure, cutout switch looks ok.

When I try to start it almost catches but then will not fire up.

Any ideas where to start looking when I get back tonight?

 

[Bay B's]

Bad distributer cap and or rotor and wires? Try reseating the ECM harness. Fuel pump? A sensor? Probably best to hook computer up to it and look at the faults.

 

[CliffA]

there is a host of things both electrical and fuel related that can cause this, but just from your description personally i would first look at a fuel issue simply because you said that the engine 'tries to fire up'....sometimes if it is an electrical issue there will not be any spark at all in the plugs so the engine should not even try to fire....

but as i stated earlier there are a lot of possible causes...it may be easier if you list all the things you check so that we can make suggestions on other things to consider and check....

cliff

 

[SeaAyeOwe]

I will certainly do that once I get to the boat - also trying to get my mechanic out there to check codes but it sounds like he is up to his neck right now. Does the IAC failure ever result in a flat out engine fail?
I have had it cause problems before but not as sudden so not sure whether the IAC has multiple fail modes. Also, the gear neutral switch failure - I would assume that would give me a smart craft code if it was field open?

 

[Bay B's]

I can't speak to the neutral switch, but my IAC failure experience would not allow the engine to idle. I could start it by putting it in neutral and increasing the throttle.

 

[SeaAyeOwe]

Ok, now I am thinking about the fail mode - and given temperatures today. I now think it may be the cool fuel unit and a vapor lock. Maybe a restriction in raw water. I will start there when I get to ten host in an hour or so.

 

[SeaAyeOwe]

Sitting in the cabin pi$$$ed right now - deep breaths.

Ok - so my mechanic called me on the way to a job, he was very confident we had a vapor lock issue possibly with a restricted raw water issue in the cool fuel unit.

So I start the process of dismantling, and of course both of those blasted plastic barbed fittings have broken. Now I need a fix for those.

I have just removed the cool fuel unit - what a PIA!!!! Really hard to get to those fixing bolts, anyway out now.

A couple of things,
- first can anyone tell me what fitting they have used to replace these barbed fittings, I have searched the threads and cannot find the thread that mentions the npt fitting size that can be bought from a hardware store to replace these plastic units.
- second, back on the original issue. When there is a vapor lock at the cooler would I expect to see fuel lines and filters all full of fuel, is the lock usuallyin the pump?

I am not sure now I have the whole unit out if I have found the original problem and my mechanic is three days away given his workload.

 

[Bow Tie]

It would not be vapor lock, vapor lock happens when the engine compartment temp causes the fuel to become vapor in your fuel line. This takes a while to happen and only while you are "not" running. First find out what the required fuel pressure is for your engine and put a fuel pressure guage on it. Your engine will probably have a shrader valve located in the front of the engine below the plenum. If you have no pressure you will know it needs a fuel pump, a dog to get to, but doable. If you have fuel pressure swap out port and starboard high energy ignition coil located on the distributor. Two screws and easy to do. One thing about vapor lock, if you ever do get it, you will need to: wait until the engine and compartment cools down completely or you'll have to toggle your on/off rocker about 2 million times and work the hell out of your throttle in order to get the fuel flowing again. Merc sells an inline 5 psi boost pump that wires into your existing fuel pump wire harness. It's the only right way to do it and you will never experience "vapor lock".

I would bet that you need a fuel pump, partsexpress.com is your best bet and price.

Bow Tie

 

[Bow Tie]

I have a lot of experience with vapor lock, if your boat was running 3700 rams and just topped, you cannot get vapor lock if the engines are running. Is your cool fuel system located under the engine attached to a raw water hose on both ends.?

Bow Tie

 

[SeaAyeOwe]

It is below the engine on the alternator side. The cool fuel unit on the port engine was significantly warmer than the starboard when I got back to my slip - having said that I limped home on the starboard and it will have been getting raw water through it.

Here are pics of the unit now out of the ER. Now I need to find the correct fitting to re-attach the raw water hoses. The searay dealer has been absolutely no help after an hour on the phone.




Whatever happens, I now need to get the cool fuel unit back in service and that is my first priority. Anyone know the correct fitting to source for a repair - you can see the salt water corrosion. I am hoping not to have to drop a boat buck on a complete new unit.

 

[kvduff]

U sure the fuel pump was coming on when you out the switch toward?


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[SeaAyeOwe]

I have a lot of experience with vapor lock, if your boat was running 3700 rams and just topped, you cannot get vapor lock if the engines are running. Is your cool fuel system located under the engine attached to a raw water hose on both ends.?

Bow Tie

Bow tie - yes a feed and return raw water hose was attached - one top one bottom, or both ends. It is the 2 bib setup.
You may be right - time will tell, I disagree about not being able to get vapor lock with engines running, this used to happen to me all the time with a previous boat in a hot climate when the raw water was restricted with crud. I could always tell when it was the cause as the cool fuel unit itself would be very warm on the outside. My unit was v. warm two hours after the engine shut down, while the good engine unit was very cool.

For now it is a moot point, as soon a si get the cool fuel unit repaired and back in place I will know if it was not the problem and can start looking elsewhere.

 

[SeaAyeOwe]

U sure the fuel pump was coming on when you out the switch toward?


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I think you are asking if I heard the fuel pump on the first start switch position yes I did - and I cycled it an number of times when trying to get it to start, though not two million times I admit:grin:

 

[skolbe]

I am sorry you are going through this. Is it Masterfab that has rebuilt some cool fuel modules? If you find the part would appreciate the share.

 

[SeaAyeOwe]

I am sorry you are going through this. Is it Masterfab that has rebuilt some cool fuel modules? If you find the part would appreciate the share.

EDIT: The only way to get an original replacement part is to buy the whole two bib unit - I will get that part number loaded up if I find it. Meanwhile I have fabricated a fix, I will start a seperate thread explaining how I did that.

I guess the real issue here on buying the replacement or fabricating is whether you want to replace a crap piece of engineering with another crap piece. I will go to my local hardware stor tomorrow to see if I can find something more robust than this and if I do I will share wit and start a new cool fuel thread with these details.

I hate marine engines sometimes. If only there was a better way to enjoy our pastime :huh:

 

[kiloil]

Could it be a water pressure sensor cutting the engine off?

 

[SeaAyeOwe]

Could it be a water pressure sensor cutting the engine off?

Usually you would see that on thesmartcraft as the preliminary alarm I think - and nada on smart craft other than low speed when ten engine stopped.

Anyways - I gotta tray to get the cool fuel unit back in service, all new filters in the fuel line up and then we will see where we are at.

 

[scoflaw]

My 2006 had the o ring fittings, later years of the cf3 had the plastic NPT water line fittings. I fitted my housing with the NPT style and a very tight fit it was

 

[paulswagelock]

To change the fittings requires using a tap to cut threads into the housing. Others have done it with success.
I had a very similar situation this year, and it ended up my cool fuel module was failing - same symptoms but happened at 4400 rpm.
Put a pressure gauge on the fuel rail - no pressure. I decided to replace the whole unit rather than try to R&R the old one. $900 later the boat runs perfect.

 

[SeaAyeOwe]

My 2006 had the o ring fittings, later years of the cf3 had the plastic NPT water line fittings. I fitted my housing with the NPT style and a very tight fit it was

Scofflaw, did you get the npt style to fit without modification or any sealer products? And did you need the bracket with them still?
I have the unit on the bench so if they can be fitted with the black npt style I may try that approach.