Brickers:

First and foremost, a happy holiday to all on the board.

Now, on to business. My 745t's engine has a slight knock, and I'm wondering if someone can tell me all about engine knock.

1) What problems, aside from piston rings/engine age, causes it?

2) What's the best way to go about getting rid of it? Cleaners, lubricants, etc.?

3) Will buying a CO reader and checking the mixture help? I've heard knock can be an indication the engine is running lean... correct?

Recently I did a weak Throttle Body Cleaning. I basically took off the air inlet pipe from the Intercooler and sprayed soem throttle body cleaner on the walls of the visible insides of teh throttle body and sprayed in the edge around the plate to clean out some of the gunk. I'm afraid some overspray may have leaked around the plate and been sucked into the engine when I next ran it. Yeah, I know, should have taken my time, but something came up and I had to hurry.

It may be my mind runing with two coincidental events, or maybe I just didn't notice the very slight knock before, but could they be related? What would the effect of some TB Cleaner being sucked in? Will any efect be mitigated and non-existant over time? The TB Cleaner has to be sucked out or burned off at some point.

Any help on this would be greatly appreciated, I'm trying to silence my engine a bit and am approaching all the little things (outisde piston slap, which I can't help) to fix it up.

Thanks,
Rick

Hi,

"Piston slap" is common in the B230FT engines I'm told. My '91 B230FT with 247K km clatters almost as loud as a small diesel below about 1300 RPM. It's a little quieter after it warms up. I've been told by two good Volvo mechanics that it's "piston slap", my valves are within spec, and the engine should last just fine as long as I take care of it. The sound is kind of annoying though. Oh well, still has lots of power :)
--
Chris. Halifax N.S. '91 745Ti, 247K km.

The term knock usually refers to ping or the sound caused by pre ignition. This is a sound not unlike shaking marbles in a tin can. It is caused by ignition being too far advanced. On most fuel enjected engines this is controlled by the ECU and knock sensor which retards the timing slightly when required. Never heard of lean mixture causing preignition though.

I think you are talking about piston slap, valve tapping or some other noise. Without hearing it it is hard to know which. If it is valves the clearance should be checked although it is rarely off spec. You do not mention mileage but sometimes we just live with the quiet noises of high mileage engines.

The cleaner will do no harm to the engine, just gets burned off.

"Never heard of lean mixture causing preignition though."

On the contrary, lean mixtures can cause preignition. The combustion chamber runs hotter on a lean mixture. Heat leads to detonation (pre-ignition). You will notice all the performance people recommend fuel enrichment to prevent detonation. Fuel mixture gauges are sold for this, and many people with highly boosted cars run additional injectors (triggered by boost pressure) to prevent lean mixture problems.