Engine pinging/knocking after shut off?

[strokeoluck]

Boat details below. Yesterday we took the boat out for it's first full day on the water. We had a great time; very glad we bought the boat! We did have a few minor issues which I'll post in the appropriate forums on iboats.

The main issue I'm concerned with is that towards the end of the day, when I turned the engine off after towing some of the kids while tubing, the engine would continue to "ping" or "knock"...basically it sounded like the engine didn't want to quit and it was sort of sputtering. This lasted about 7-10 seconds. It happened 2-3 times. If it matters we were on an inland lake for about five hours total, with maybe 90 minutes of "running time" towing kids around on tubes. The boat was filled with 87 octane gas purchased just a few weeks ago (previous owner left it empty in fall of '08; we purchased it in 12/08 and filled it for the first time just recently).

Thoughts on how I correct this?

 

[Anchor Management 1]

Re: Engine pinging/knocking after shut off?

Check the ignition timing sounds like it is off.

 

[gshldon]

Re: Engine pinging/knocking after shut off?

i would also tend to try and run a higher octane gas, i use nothing but premium in my boat along with all my other small engines. The reason for this is that since they are not used all the time like your car, the gas can break down and start to cause more problems with the carb getting gummed up.

Just my thoughts. I have never had an issue with my boat since running only premium fuel

 

[strokeoluck]

Re: Engine pinging/knocking after shut off?

i would also tend to try and run a higher octane gas

I was thinking I might try the same thing, but wanted to hear from others if it worked. That would certainly be a simple and relatively inexpensive solution if it works. I would consider yesterday a full half day on the water and we used about 8 gallons. So the difference in fuel costs is nominal for us. I'll give it a shot.

 

[danond]

Re: Engine pinging/knocking after shut off?

Changing fuel octane is a bandaid. Get the timing set properly so it doesn't detonate/diesel and you'll actually have fixed the problem!

 

[rs2k]

Re: Engine pinging/knocking after shut off?

If you're going to use high octane fuel then make sure you get it at a well traveled gas station. The high octane in "off the path" gas stations can sometimes be worse than fresh 87.

 

[strokeoluck]

Re: Engine pinging/knocking after shut off?

Changing fuel octane is a bandaid. Get the timing set properly so it doesn't detonate/diesel and you'll actually have fixed the problem!

Can I use the higher octane through the season and then ask the marine shop guys to check out the timing in late Fall?

 

[rs2k]

Re: Engine pinging/knocking after shut off?

Can I use the higher octane through the season and then ask the marine shop guys to check out the timing in late Fall?

Detonation and dieseling may also mean you have another issue lurking inside your motor. Dieseling, which is when and engine continues to run once it shuts down, happens when fuel ignites without a spark. This can only be caused by low octane fuel or an over heated engine. The over heating can be caused by a cooling problem, head gasket problems, or by incorrect ignition timing. Since the engine is running okay (what are the temps?) my best guess is that you have a tank of old gasoline.

Fill it up with premium fuel and see if it has the same problem if you don't want to take it in and have the timing checked. Just make sure you keep a close eye on the engine and gauges the next time you go out. Also keep an ear on it. Pinging during high loads can destroy an engine in short order. It can melt and put hols in the pistons. It's also VERY VERY VERY hard on engine bearings.

I hope I didn't scare you too much.

 

[gshldon]

Re: Engine pinging/knocking after shut off?

after trying the higher octane fuel, see if that solves your problem then go from there.

I must ask how does the motor run at idle and and will under power, does there appear to be any miss or iradic idle going on, if the timing was off just like in a car you would be able to tell while the engine is at idle, if it is running really rough or not.

 

[dan t.]

Re: Engine pinging/knocking after shut off?

sounds like diesling or it is sometimes called run on,causes: late timing, to high idle speed,carbon build up, too hot plugs, poor quality fuel. beware, an engine with run on can actualy stop then run backwards briefly,you can imagine the conciquences in a marine set up,big gulp!

 

[strokeoluck]

Re: Engine pinging/knocking after shut off?

I must ask how does the motor run at idle and and will under power, does there appear to be any miss or iradic idle going on

It ran fine 99% of the time (the other 1% being when it was "dieseling" after shut off).

As a reminder, it only happened towards the end of the day. I kept an eye on my gauges all day (see my other post re: a "bouncing" fuel gauge) and don't recall seeing anything unusual re: engine temp. Also, the previous owner left the gas tank dry (almost) so I filled it up with fresh gas earlier this month - and it was from a busy gas station.

I'll fill 'er up with the higher octane stuff the next few times and see how she holds up. Thanks everyone!

 

[Silvertip]

Re: Engine pinging/knocking after shut off?

My gosh man -- you have a timing/idle speed problem. Putting it off until fall can result in you having to post here again with another more serious engine problem. The engine needs attention NOW -- not next week or next month. As the guy on the TV ad says -- pay me now or pay me a lot more later.

TIP #1: Idle the engine for three minutes or more before shutting down during a long hard run.

TIP #2: Your engine is designed to run on 87 octane regular grade fuel. If it doesn't run good with that grade there is something wrong. Fix it to avoid more serious future problems.

TIP #3: Check the tachometer to see what the idle speed is. The solution may be as simple as an idle speed adjustment.

TIP #4: Check the engine TEMP gauge while skiing/tubing to see if there is a marginal overheat condition that is not high enough to trip the alarm. You may have a cooling system problem such as a bad thermostat, bad water pump or clogged risers.

TIP #5: Continuing to run ANY engine with a problem can and generally does result in a more serious problem than one first observed. Gauges are installed for a reason but they mean nothing if one never looks at them or doesn't understand what they mean.

CONCLUSION: Engines don't generally wear out -- their operators KILL them!

 

[IVAZ]

Re: Engine pinging/knocking after shut off?

I agree with everyone that?s advising you to fix it now rather than later. When was the last time you gave it a tune up? As some have suggested, check the idle and timing. It very well could be an easy fix. I seriously doubt a change in octane will fix anything.

 

[Maclin]

Re: Engine pinging/knocking after shut off?

It may be as simple as letting it idle for a minute or so before shutting it down. I know that may not always seem possible but it is one of the recommended "fixes' for run on. Start the blower just before you settle down to idle, and let the engine cool down at idle for a minute or so before shutting it off.

Your spark plugs could be the wrong heat range, make sure they are in spec. If it has not been tuned recently then a full tuneup may be in order.

I also come down on the "octane is not the answer" side of the coin.