Pinging

"Hi all this is going to be fa

"Hi all this is going to be fairly long winded so please bear with me.
I have a 2001 model 4.3 litre mercruiser with TBI in a Haines Signature Bowrider, I have had this boat for about 9 months. The engine is a long motor quicksilver rebuild with new just about everything being new except starter motor and alternater. When I took ownership the dealers mechanic told me to run the boat on Premium unleaded as that is what they recommend all customers to run in their mercruiser engines. I took this as gospel until I stumbled across this website and saw posts that said mercruisers are designed to run standard unleaded 87 octane. So trying to save a few bucks I decided to give it a go. No immediate differences were noticed as I was just topping up on a half full tank. I must also add that before I tried the 87 octane their was sometimes the occasional pinging or knocking that would come from the engine when under extreme load e.g pulling up a skier or when WOT around 4500 rpm.
After the addition of standard unleaded the pinging was no worse than before. So after a couple of months of good running and really no pinging, the engine decided to start to ping a little. After a bit of research on the net about pinging, came up with a few possible causes. Timing too advance, low octane fuel and carbon deposits in the cylinders. The first two looked pretty easy to deal with. Retarded the timing till pinging went but the boat lacked lot of power and would only WOT to abot 3500 rpm. HAve now drained the fuel tank in preparation to put premium into the tank. The other thing that was observed at the time of pinging was the tacho would be really erratic and even if there was a small ping you could see the tacho jump. Am I going down the wrong path of timing or octane problems or do I have some sort of electrical problem. I just can't understand how pinging would affect the tacho. Thanks to all with your replies. By the way even when the timing was retarded it did not take away the pinging.

Cheers guys and gals"

That engine should run fine on

That engine should run fine on 87 octane. Usually timing too far advanced does that but apparently something else is wrong. Also the mechanic either is unskilled or is covering something up.

I had similar problem with a t

I had similar problem with a truck and I ran dobule concentrated fuel system cleaner and it took care of the problem. It wasn't even the good stuff. It was store brand at $1.99 per bottle. It called fro 1 bottle per 20 gallons so I ran 2 bottles. A can of seaform may do the trick as well.

"I agree with EfO and w2f. Re

"I agree with EfO and w2f. Reset the timing to specs. Check the wires on the coil for tight fit. If wiring is ok then disconnect the tach. If the pinging stops and the accel. problem is gone, replace the tach.

If the accel. and tach. problem is solved but the pinging persists, inspect the ignition components for any wear; cap and rotor--replace if worn or suspect. Pull the plugs and clean/regap to .045 if platinum or replace if center electrode tip is rounded. Dump a can of SEAFOAM in the fuel tank before filling it w/a name brand fuel; Shell, Sunoco, Mobil, etc. Try running the engine w/10 gals. of 87 octane until the tank is near empty. If the pinging persists, add a can of Mercruiser carbon remover and step the octane up to 89 grade and run 10 more gallons. Let us know what you find."

"Scott,
What I would do is

"Scott,
What I would do is first make sure the fuel is ok by adding Sta-bil and E-zorb.I next would change the fuel filter.The 87 will be fine but 89 would be better.A complete tight tune-up is next, missing nothing, as I am not so sure you are running properly on all 6 cylinders with the statement about the tach jumping.The timing should be set exactly what is called for.Theory is that if the fuel is ok,engine is electrically ok,then you should be ok as long as the TBI is working properly.Thats what I think from the info givin and I think you will find your problem from doing the above.......Todd"

"Scott...
I know you said tha

"Scott...
I know you said that everything was replaced, so you shouldn't suspect carbon deposits anywhere. BUT during re-assy of the engine, there is the possibility that something wasn't buttoned up tight enough or properly. There could be a vacuum leak in there somewhere causing a lean air fuel mix and raising combustion chamber temps to cause that ping. Check around the bottom of the carb (I know its a TBI)for a vacuum leak at the base gasket, miss routed vacuum line, vacuun line off, whatever. Listen for it whistling as its sucking air. How does it idle? If it idles rough, use a do-it-yourself at home propane plumbing torch to try and find the vacuum leak. Open the valve up on the torch, don't light it and go in around the bottom of the carb and sides of the intake manifold (with engine running) to see if the idle smoothes out. As the vacuum leak sucks in that raw propane it'll smooth out the idle.

Wrench"

Thanks for all the input guys.

Thanks for all the input guys. As was said in my original post I have drained all the fuel out in preparation to put in some premium fuel. Unfortunately I won't be heading out to the water again for a couple of weeks so I am not going to be able to give any feedback till then. I talked to my mechanic today and told him the symptoms and the first question he asked was if I was still running premium fuel. I told him no as I had read that the mercruiser web site states they are designed to run on standard unleaded. He said that mercruiser australia recommends that premium fuel be used. I have no reason to not believe him especially when one of the walls in his office is covered by Mercruiser attainment certificates for one thing and another. I guess I will just have to wait and see in a couple of weeks when I get to go out again.

Once again a big thanks to all with their invaluable information

Cheers
Scott

"Just an update for everyone.

"Just an update for everyone. The timing was set at 12 degrees BTDC and was brought back to 8 degrees BTDC. Fuel has been changed over to premium. Took boat out today for a short run to see if it made a difference, and it did. Although I can still hear the engine ping a little bit as it gets up to full rpm. The tacho has settled down a bit but still goes up past 5500rpm then settles back to about 4600 at WOT with a bit of spiking every now and then. So I think everyone that posted a reply was on the right track. I just need to find out why the tacho is still spiking. Going out on the water on the weekend so maybe will come across something else.

Cheers

Scott"

bump

bump

Scott:

"tacho has settl

Scott:

"tacho has settled down a bit but still goes up past 5500rpm then settles back to about 4600 at WOT with a bit of spiking every now and then"

I'll bet the tacho is dying. Mine did that until I replaced it.

"still hear the engine ping a little bit as it gets up to full rpm"

JUST A THOUGHT:
Auto mfgs. state that condition (ping a little bit) is normal and not an issue because the engine is running at its optimum.

Thanks Guy

Thanks Guy

Scott:

Our pleasure. Let u

Scott:

Our pleasure. Let us know the final outcome. One last thought: does the engine have a knock sensor? Test it. Use the Handle of a hammer and wrap the metal hard with handle end TWICE around the sensor while the engine is idling; if it is working RPMs should change as the timing is retarded by the computer to compensate for the knock.