6.0L V8-380-C-D Stalls on Acceleration

[david.aka.butch]

My 2015 Cobalt R5 will start instantly every time I turn the key and I can use the throttle to engage the prop and idle along but as soon as I push the throttle forward to speed up the engine dies. I can turn the key to the off position then back to start and the engine fires right back up. I tried taking my boat to the closest Cobalt dealership (1.5 hours away) but they just charged me a bunch of money and didn't solve my problem. My fuel pump had been making a high pitch whining sound for a while so I thought perhaps that was the problem so I did a complete strip down and rebuild of the fuel pump assembly, replacing both the high and low pressure pumps. That did solve the whining issue but the boat is still stalling when I try to accelerate. When idling along I will also get an occasional momentary alarm. It just comes and goes, not affecting the engine running, but interestingly I don't seem to be getting any fault codes. I don't have an actual diagnostic scanner (any recommendations would be appreciated) but I did purchase a Volvo Penta Easy Connect a few years back and it is not showing any alerts. (It has in the past when I had an issue with a sensor so I believe it is working correctly). Any recommendations on where I should look next would be greatly appreciated!

[AsLan7]

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So glad you found us d.a.b.

When your technician attached their code reader, what codes popped up?

Post a pic when you get a chance.

And welcome aboard mate.

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[jhnmdahl]

It does sound like a fuel flow problem - either the pump, a clogged fuel filter, or something similar, but it could be any number of other things too. One thing you could do without a trip to a shop is pull the plugs and see what they look like - lean, normal, fouled, etc.. It's also possible you just got some bad gas or it turned old.

[david.aka.butch]

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So glad you found us d.a.b.

When your technician attached their code reader, what codes popped up?

Post a pic when you get a chance.

And welcome aboard mate.

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I don't believe the technician attached any diagnostic tool/code reader. If they did I wasn't provided any of that information. One thing is for certain, they never put it in the water to test drive it or else they would have immediately experienced the problem.

R/
David

[david.aka.butch]

It does sound like a fuel flow problem - either the pump, a clogged fuel filter, or something similar, but it could be any number of other things too. One thing you could do without a trip to a shop is pull the plugs and see what they look like - lean, normal, fouled, etc.. It's also possible you just got some bad gas or it turned old.

As mentioned earlier, I did a complete rebuild of the fuel pump so it is basically new. I also replaced the fuel filter even though I had just put a new one on a few months ago. I will check the plugs, but it seems like that may cause the engine to run rough but not necessarily just die. When the engine stalls it doesn't sputter or anything like that, it just cuts completely off. Like throwing a switch.

R/
David

[jhnmdahl]

Code reader during operation would be my next step. Most things I can think of would cause a stutter rather than a complete and sudden switching off, other than something like a bad electrical connection that shuts power to the computer or engine off when it vibrates or is under load. Realistically, we're just spitballing, based on some pretty broad symptoms.

[Kate]

Start fine, then stalls at acceleration: That sounds like limp mode.

Sometimes, disconnecting the battery for a bit then reconnecting can reset the system and solve the problem.

Other times, there's a long list of problems that can cause limp mode, e.g., restricted fuel flow somewhere, low fluids, overheating, faulty sensors, trans problems.

[NautiWeasel]

Based off of my experience with the same engine... I'd say it's fuel related as well. This engine seems to be very picky about fuel flow. I would do as stated above, and change the fuel filter (water separator) and change the spark plugs for good measure. Together, those things are about $100, and might take an hour or so (at most, if you're mechanically inclined). The plugs are AC Delco: 41-110 for OEM. I would start there, and see if that helps. If nothing else, now you know you have fresh plugs after 10 years!