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Re: Any particular year? Answers Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 25 May 2005 06:19:28
In Reply to: Re: Any particular year? Answers, Buz, Tue, 24 May 2005 12:24:39 Members do not see ads below this line. - Help Keep This Site Online - Signup |
If an engine is going to knock, hot and boosting is the most common time. An engine is most likely to knock at high air temperatures, and under boost. When it's hot out, the air coming into the engine is that much hotter, and the intercooler, which uses outside air, can't cool the intake charge as well. Yes, hot air is less dense, but the turbo does a fine job of compressing it. So the air coming into the chamber is hotter than on a cool day. If the problem is the intake charge burning too soon, starting with something hotter is more likely to burn sooner.
When boosting, the pressure in the cylinder is higher (than not boosting) The intake charge is supposed to burn when the spark plug ignites it. It is a very controlled process, and the idea is to produce expanding gas to push the piston down. If you simply squeeze the charge until it expodes, it burns differently. And too soon. Obviously, under boost, the intake charge in the piston is already compressed - if the engine has a tendency to squeeze the charge into pre-ignition, the most likely time is under boost.
So a normal engine is more likely to knock when the air is hot or under boost.
A couple of things are going on here-
The biggest worry is that the APC system isn't kicking in, if you can actually hear knock. Something is wrong there. It should be limiting boost. You might have a faulty BPC valve (mounted on the radiator). When they fail, they usually limit you to Base Boost, or provide wild amounts of boost. But it is possible that it just wouldn't limit boost.
In the meantime, run higher octane fuel. Techron is good stuff, but it doesn't make gasoline less likey to detonate. Only octane does that. Knock just isn't annoying - it WILL destroy the engine. Those are explosions in there. Each one is taking small chunks out of the top of your pistons. I have actually seen uncontrolled knock blow a hole through a piston. (usually only one - the engine stops before you get to completely destroy any more).
When it comes to spark plugs, you should always use the exact NGK plugs specified in the manual - I believe it's the BCPR7ES. And gapped per the manual. NEVER substitue, even if the parts guy says the BelchFire 500X is an exact replacement. The DI cassette in your car was designed to work with those exact NGK plugs. Others may work. Or not. But if you are chasing problems, messing about with other plugs is the wrong approach.
The spark plugs live in the engine, and tell what's going on during combustion. If you're running rich, they'll be black. If you're running lean, they'll be white. If you're running really lean, they'll look melted and have yellow junk welded to them. If the gap gets too big, the engine will miss under boost. Look at the plugs to see what is going on.
If you are getting full boost (needle all the way to the end of the yellow) and you can hear knock, something is wrong with the APC. Try this trick - find a nice long hill and charge up it, so you can get full boost. With your left foot, GENTLY touch the brake, so that the brake lights come on (you'll hear the switch click) but you aren't braking hard. The boost gauge should drop down to mid yellow. That's because the system limits boost under braking (makes sense - why have full boost when trying to stop?). If it doesn't, there is an APC system problem to chase.
posted by 192.249....
, Mon, 23 May 2005 08:37:51, Tue, 24 May 2005 06:33:31, Wed, 25 May 2005 06:19:28 <-- Viewing This Message
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