Anyone experienced "Carbon knock" on 4.0 SOHC?

[Crash513]

I have had a problem with a rattling noise on light to medium acceleration for the last several months. This sound is a light tapping, which varies depending on load. It seems more noticable when the car is cold, but it is still slightly noticeable when warmed up.

The service writer at my dealership (who I have known for years and trust) has diagnosed this problem as a condition called "Carbon knock". His theory is that carbon buildup in the combustion chambers is causing pre-ignition. He recommended that I "drive the snot out of it" for a few days, flooring the car to redline whenever I get on a freeway onramp. I was a little skeptical about this at first, but for the last 2 weeks, I have been punching it out at least a few times a day when the safe opportunity to do so arises. Suprisingly, it seems to be working, as the condition has improved a great deal, but I still notice a vey slight knock when cold. The other suggestions he gave me to resolve this problem were:

1. Buy better gas (not higher Octane, just a better brand.
2. Perform a "top soak" by injecting a solvent solution into the cylynders and letting it break down the remaining carbon.
3. Injecting water into the intake charge to break the carbon down.

I did switch from ARCO Uleaded (RON 87) to Unocal 76 Premium (RON 89) which may have helped. This is not 91 Octane super uleaded, but the ARCO gas has a reputation for being pretty crappy, so I wanted to try it.

I am now wondering if I should try the "top soak" process, or just keep punching out the motor when I can to see if I can get rid of the remaining carbon. Anyone have any other suggestions for an action plan? This is no longer a debilitating problem, but it is a nusaince, and I sure don't want to end up with an air conditioned piston or busted ring due to preignition. Any suggestions?

OBTW, the timing chain, tensioners, and blocks were replaced about 9 months ago for the noise problem, which also sounds like tappet noise or preignition. This is not the same sound, and I think the new chain is fine. The Engine has about 58K miles on it right now.

Any suggestions or input would be much appreciated!

Thanks,

[Edited by Crash513 on 10-25-2000 at 10:07 AM]

 

[Goober]

You could use a an injector cleaner. Since it sprays in the chamber it may help to get rid of some of the carbon. I have the same little ticking when going at highway speed and give it a little more gas or start going up a hill. It starts to sound a little like a diesel. I always thought it was just that way. Of course, I have so many rattles in my truck, what's one more!

 

[Cameron]

It sounds like knock to me. I would be surprised if your truck with less then 60 K on the odometer and less then 3 years old would have a large carbon buildup. Try one tank of higher octane gas and see if the problem goes away.

How old are your plugs, wires?

Just some thoughts.

Let us know.

 

[AgExplorer]

You may want try AMSOIL's Power Foam. I does an excellent job of cleaning out carbon and other buildup. A Ford dealership will charge you $120 or more to do the same thing.