rough idle

[Ronald]

hi guy s I have a 2014 sd 26 cobalt with 180 hours with a 380 hp the engine is shaking like its running on 7 not 8 cylinder at idle I went out on the ocean today same thing at 4000 rpm it never did that before whats up a call the service guy at cobalt dealer he told me to put some ethanol treatment in the gas tank and call me back Monday did someone ever had this problem before thanks.

[Big Block Power]

Welcome from Wisconsin.
If it's actually running on 7cyl. I would start with spark plugs. What is the maint history on the engine. Replace the fuel filter. Could be a coil also. Buy a spark tester from a auto store and test each one. See if one isn't firing. Then you can swap could to see if that's it. Also can be a injector. If you unplug one at a time and the rpm doesn't change that is your cylinder to go after spark or fuel.

[ajcampen]

Your engine is still under warranty, right? I would give it to them and say have at it

[Big Block Power]

Your engine is still under warranty, right? I would give it to them and say have at it

Good call. I have old stuff so I forget about the warranty.lol

[AsLan7]

.
Hey Ronald, welcome aboard. So glad you found us!

The majority of the time, rough running marine engines are usually the result of something simple such as water in the gas or a clogged fuel filter. My guess--water in your gas.

Most likely you have gasoline in your boat tank which contains Ethanol. Ethanol absorbs moisture from the air. Your conditions sound similar to the experience in this link:

http://www.postandcourier.com/news/boat ... b6dc4.html

Marine tech quote from the rough running engine article...
"The biggest problem is ethanol which is alcohol-based and alcohol absorbs moisture from the atmosphere," Murphy explained. "Over a period of months, it can add up to a half-gallon, maybe as much as a gallon of water."

"That water separates from the gas and sinks to the bottom of the fuel tank. When a boat takes off, the bow rises and the fuel rushes to the lowest spot in the tank, which is where the pickup tube is located. Water is sucked into the engine, causing it to misfire."



Question... How long was your gasoline sitting in the tank since your last fill up?
I would fill up with a fresh tank of gasoline and add some Stabil Ethanol treatment or SeaFoam treatment to your tank--both of which can be purchased at your local Walmart for less than $10. Great insurance against gas going bad after being left unattended for over a month. Now you just need to run that bad gas out of the tank.

If you are still under warranty, your local marine tech will be able to diagnose this quickly. Just give him (or her) a call.

So great to have you here, Ronald. Feel free to introduce yourself in a new thread and how you got into a Cobalt. We love pics too!

.

[SWAGNATIONS]

.
Hey Ronald, welcome aboard. So glad you found us!

The majority of the time, rough running marine engines are usually the result of something simple such as water in the gas or a clogged fuel filter. My guess--water in your gas.

Most likely you have gasoline in your boat tank which contains Ethanol. Ethanol absorbs moisture from the air. Your conditions sound similar to the experience in this link:

http://www.postandcourier.com/news/boat ... b6dc4.html

Marine tech quote from the rough running engine article...
"The biggest problem is ethanol which is alcohol-based and alcohol absorbs moisture from the atmosphere," Murphy explained. "Over a period of months, it can add up to a half-gallon, maybe as much as a gallon of water."

"That water separates from the gas and sinks to the bottom of the fuel tank. When a boat takes off, the bow rises and the fuel rushes to the lowest spot in the tank, which is where the pickup tube is located. Water is sucked into the engine, causing it to misfire."



Question... How long was your gasoline sitting in the tank since your last fill up?
I would fill up with a fresh tank of gasoline and add some Stabil Ethanol treatment or SeaFoam treatment to your tank--both of which can be purchased at your local Walmart for less than $10. Great insurance against gas going bad after being left unattended for over a month. Now you just need to run that bad gas out of the tank.

If you are still under warranty, your local marine tech will be able to diagnose this quickly. Just give him (or her) a call.

So great to have you here, Ronald. Feel free to introduce yourself in a new thread and how you got into a Cobalt. We love pics too!

.

This is my guess...or spark plug/sp wire

[ajcampen]

Try valvtect product for ethanol treatment

[jhnmdahl]

Clean gas, check the plug wires, and replace the spark plugs will cost relatively little (maybe even less trouble than driving the boat back the dealer). And Sta-bil or some other gas treatment every time if you have to use ethanol gas is a great idea. Beyond that, I'd let them look at it as a warranty issue.

Please let us know what you found when you get it figured out!

[Ytmsn]

I agree. It sounds like bad gas and a plugged injector or fouled plug. I'd siphon what you have out, put in fresh gas, change your fuel filter and run a couple of cans a sea foam through. I think sea foam is better at drying up and cleaning out While sta-bil seems to be better at stabilizing fuel while it sets, but they may do the same thing. I use both of them.

While it's running you can pull each plug wire off until you find the bad cylinder. You may have to change the plug or pull the injector and clean it.

And then going forward avoid ethanol or use sta-bil ethanol treatment every time you put gas in if you cant get straight gas.

[AsLan7]

.
And remember, once this gasoline breakdown begins, there is no additive product that can "restore" it back to it's original state.

You are simply pouring an additive into the tank to help "absorb" the water --to help eliminate the engine hesitation you are experiencing. Still need to run fresh gas thru your system.
.

[Ronald]

thanks guy"s im working on it im trying to have the boat service at the dealer but they're backed up for a month and now I found a mobile service guy coming to run a laptop on it, I tried pulling plugs wire out one at a time it didn't change the idle. should I still change plugs and wire with new aftermarket better one 's i justs have 180 hours on the engine or go with oem parts.

[Big Block Power]

thanks guy"s im working on it im trying to have the boat service at the dealer but they're backed up for a month and now I found a mobile service guy coming to run a laptop on it, I tried pulling plugs wire out one at a time it didn't change the idle. should I still change plugs and wire with new aftermarket better one 's i justs have 180 hours on the engine or go with oem parts.

If the plugs have never been changed its not a bad idea to change them. That way you know when they have been changed. Second no don't use after market plugs and wires. Match what's in there prob both AC Delco.
If they look ok sure you can still run them but for the extra couple bucks per plug and you already have them out mine as well replace them. What kind of gas do you run in her?

[AsLan7]

Laptop diagnostic will help.
Like BbP said, new plugs will be for peace of mind.
I prefer OEM as well.
How old is your gas?

[Ytmsn]

Wait, you pulled each plug wire and it didn't change how it ran? It didn't die? It shouldn't change how it idles when you get to the bad cylinder..but I figured it would have died running on 6.

[Ronald]

I had a half tank in storage from june to September the boat is in florida I m in Vermont for the summer when I got back it rand good for a for a couple of time and then it started running rough so I tried seafoam I had stabil storage in it all summer the red stabil I fild it I top it of this weekend with new gas it clear up for a couple of miles on the intracoatal and when you arrive at wake zone it started to shake again so I went on the ocean for a ride it never clear up again even at 4000rpm il will be changing the plug tomorrow with oem plugs will keep you updated thanks