Engine shutting off occasionally when warm

[Mozart]

Hello, I had surging problem with my 5.7L vortec inboard in the summer. It seems to have been fixed after practically changing all electronic sensors and parts on the engine. Now the engine when running continuously at high speed has no problem. (Ie slow cruise out of harbour then high speed to fishing ground)
However, if I go speed up, slow down drop trap, speed up, slow down drop trap, speed up then engine coughs and dies. Restart, engine would run for a sec or two then shuts down. However, if I leave ignition at on till fuel pump stops then start the engine would run okay at low rev, and when I try to speed up it’ll cough and die. Leave the engine to cool down for about 10min it’ll accelerate okay to planning speed, and will be okay so long I don’t slow down and speed up. It’ll run fine. What do you think might be causing the problem?
Thank you

 

[Doug]

Check you wires going to your starter for cracks and a good connection. If the positive cable voltage fluctuates down the computer brain which runs the engine timing will shut the engine down. I had the same problem and changed everything out before, I decided to check the starter connections and found a crack in the wire which dropped the voltage. I check my manual and there is a short paragraph that notes voltage drop issues in the distributor due to that cable. Once it cools down it ran ok until I started power up and it would die.

Good luck

 

[Max123]

On an issue where the motor periodically dies, I'd be checking over all my electrical connections (including battery connection) for something simple or obvious. That said, based on the symptoms you describe i'd be homing in on a failing fuel pump, or a clogged fuel filter.

On an inboard, I suspect you have a high pressure fuel pump in the tank. These in-tank fuel pumps typically have a strainer built into them (you replace the entire thing as a unit), or an in-line high pressure fuel filter which can be replaced on its own. If you can get a pressure gauge on the fuel line, it would tell you a lot (unable to build correct fuel pressure).

 

[Offshore]

Carb or injectors?

 

[salmonkiller01]

Have ran a Volvo injected, had a similar issue and it was the fuel pump. It would heat up and stop working then would sit for a bit and work again. Really hard to diagnose, should have done a draw test on it to see if it was within specs

 

[Max123]

Have ran a Volvo injected, had a similar issue and it was the fuel pump. It would heat up and stop working then would sit for a bit and work again. Really hard to diagnose, should have done a draw test on it to see if it was within specs

Exactly - had the same issue in an old car of mine. Often the fuel filter is partially clogged, stresses the pump, causes it to overheat and stop work. Cools down and starts working again (for a while at least). Can be a frustrating diagnosis, because invariably when you take it to the mechanic it works fine.

 

[kingblazer84]

Fuel pressure regulator bleeding pressure away but you’ll need to hook up a mechanical gauge and test pressure on and off load etc to prove out if fuel is bleeding back once it’s shut down. Either way sounds fueling related atleast to me right now.

 

[Mozart]

Carb or injectors?

It's an injector.

Thank you for al the tips.
I've changed fuel pumps (LP and HP) But not filter (fuel and separator filter). I'll do that first. If problem solved that'll be great if not then I'll go get gauge to measure fuel pressure.

Thank you

 

[salmonkiller01]

It's an injector.

Thank you for al the tips.
I've changed fuel pumps (LP and HP) But not filter (fuel and separator filter). I'll do that first. If problem solved that'll be great if not then I'll go get gauge to measure fuel pressure.

Thank you

Definetly change filters. All it takes is one fill at the wrong time. I always fill at the same place, always clean except once, got a bunch of dirt and plugged the filter. Took about a year to get back to normal dirt volume in the filter Has not happened since but I did sell the boat

 

[Mozart]

Changed filter engine performed better but still have occasional pressure drops. Decided to add a lift pump which can be turned on manually. Today went out to try and when engine is having pressure drops I turned on the aux lift pump for about 10 sec and engine run fine for rest of the trip. May be vapour lock? Not sure but. Today for the first time this year we went out and came back with main engine. Thank you all for your input.

 

[Max123]

I'd proceed carefully - especially if you already replaced the fuel pump on the engine (so presumably no longer the source of the issue). My guess is that you have a small leak in your fuel system before the engine and you were sucking air and the pump was losing its prime. By adding a lift pump, fuel now gets to the engine - but might be dripping out at a fitting somewhere.


The fuel pump on your engine sucks fuel from the tank and would be sensitive to a bad fitting in the line (it potentially wouldn't leak fuel, but would suck air). A lift pump is pushing fuel from your tanks, so a bad fitting is now going to drip fuel. By turning on the lift pump for a few seconds, you are basically just priming a line that lost pressure or was sucking air.

Suggest pressure testing the fuel system between the engine and tank.

 

[Mozart]

I've always thought it's vapour lock but that's a likely scenario. I'll check all fittings

 

[SpringFever552]

If its tbi and shuts down again when hot, have you checked to see of you have fuel at carb, electric pump?
Key on , engine NOT running, while looking into carb cycle throttle a few times, Getting fuel? If yes
It could be what I had, a bad coil that caused this same issue when hot..

 

[Mozart]

Found out where it's loosing fuel pressure. Bulb pump to kicker was failing. Sunday trip put engine ran well. Thank you all for the help