5.0 surges/cuts out for a second

[Kman530]

Hello,
I recently purchased a 2003 Bayliner 2150 with the Mercruiser 5.0. I’m experiencing what feels like the engine cuts out for a second and comes back while cruising at 2500-3000 RPM. It only happens for a second and comes right back but I haven’t been able to figure out why. I changed the cap/rotor, plugs, plug wires, fuel filter and coil as a tuneup but it’s still there. I did notice that it seems to only occur when the fuel tank is full. I took it out one weekend with a full tank and it would intermittently cut out and come back. After three hours of running it and with a 3/4 of a tank, the next weekend the problem didn’t occur so I figured that maybe I had some water in the fuel or something. Filled the tank up and took it out the following weekend and it’s back. Any thoughts?

 

[Kman530]

I guess the first thing I’ll do it make sure the vent isn’t clogged for the tank.

 

[QBhoy]

This a carb or MPi

 

[Kman530]

Sorry, it has a carb

 

[Kman530]

So I took the vent line off and blew low PSI air through it. It sounded like it had good flow. I also checked the ignition switch and all the connections are tight.

 

[Kman530]

Thoughts?

 

[Scott06]

Check the contents of your fuel filter for anything but clean gas.

When this happens three things I would check to see if its fuel or spark

unscrew the fuel filler cap see if it makes a difference. The fact that you are correlating time running and fuel tank level still points to clogged vent

take flame arrestor off pump the throttle and look down the carb bores - do you have a good shot coming out of the accelerator pump? If not carb may be empty of fuel

bring a timing light see if the spark is consistent. maybe use a spark gap tester or igniton analzyer to test strength of spark vs when its running well. just looking for loss of spark. The ignition analyzer goes over the plug wires and gives how many kV are being delivered tot he plugs.

other thoughts
man overboard switch Ive had mine indavertantly click off when im on it pretty good in rougher water

disconnect tach incase it is shorting out ignition

Antisiphon valve on top of fuel pick up - although I dont think this would be inttermittent

Shift interrupt getting activated by somehting loose on shift plate

check 12v supply connections from engine to ignition switch at helm and back to positive side of coil for corrosion or loose connections.

 

[Kman530]

Check the contents of your fuel filter for anything but clean gas.

When this happens three things I would check to see if its fuel or spark

unscrew the fuel filler cap see if it makes a difference. The fact that you are correlating time running and fuel tank level still points to clogged vent

take flame arrestor off pump the throttle and look down the carb bores - do you have a good shot coming out of the accelerator pump? If not carb may be empty of fuel

bring a timing light see if the spark is consistent. maybe use a spark gap tester or igniton analzyer to test strength of spark vs when its running well. just looking for loss of spark. The ignition analyzer goes over the plug wires and gives how many kV are being delivered tot he plugs.

other thoughts
man overboard switch Ive had mine indavertantly click off when im on it pretty good in rougher water

disconnect tach incase it is shorting out ignition

Antisiphon valve on top of fuel pick up - although I dont think this would be inttermittent

Shift interrupt getting activated by somehting loose on shift plate

check 12v supply connections from engine to ignition switch at helm and back to positive side of coil for corrosion or loose connections.

Thank you for the reply! I took the vent line off the tank and blew some air through it, seemed like there was some resistance at first but hard to tell. I also changed the ignition coil which was the original. I had about 3/4 of a tank and ran it for a few hours and didn’t experience the issue. I’ll fill it up full again this weekend and see if that has any effect. I’ll start burning down the list you provided if it comes back. Appreciate the help!

 

[Rick Stephens]

If an Alpha drive, might be something misadjusted on the shift interrupt allowing vibration to engage it.

Might be a loose or corroded ground wire. Dirty contact on any connector in the ignition system.

As stated, a loose connection at the safety lanyard switch.

Loose or dirty wires at the ignition switch. Bad ignition switch.