I think my car is knocking. I had bumped up the timing last fall and didn't have any problems, but now that it's really cold, I think she knocks at low speeds. I always run 93 octane and occasionally an octane booster of some sort. I really like the increase in power from doing this, but I'm a little concerned as to what the "possible" knocking might be doing to my engine.

Hell, I don't even know what knocking sounds like. Help.

 

The best way to determine if there is knock is to get a scanner. That would be the easiest to. Usually knock is from WOT, but if it is a low speed, then there might be something else wrong. I have heard headers, broken motor mounts, broken transmission mounts, and even bumps in the road have caused a couple counts on the knock sensor.

I wouldn't bump up the timing on the car, I would only use the computer. The computer will think it is at 6*, when you have it a 10*. I can't remember which one it does, but it does one of the two following things.

1) It doesn't matter, because if the car is to advance the timing to 23*, it will only hit 23*. That means that you raised it up for idle.

2) You bumped it up across the whole board, and most likley made knock, higher RPM is where knock is most probable.

Make sense? I might be wrong about both of those, but on the DIY/PROM board they said that it doesn't matter. Might do a search for timing advance or distributor advance on that board.

Knock sound like pinging. I don't think that you would have any harming knock, but you will lose power with knock. It retards the timing back down when knock is picked up.

 

by bumping up the timing via the distrubtor you are raising the BASE timing... and the timing in the chip just adds to that... so if you have base timing at 6* and in the chip its 23* then you have 29* of TOTAL TIMING... so by bumping the base up to 10* you get 27* total timing... more spark means you can get more power... IF YOU HAVE ENOUGH FUEL... knock comes from having too much timing and not enough gas causing a lean condition... when you get knock the knock sensor will retard timing until the knock goes away... so you can bump timing up 4* from 6* to 10* but end up getting like 13* knock retard for your troubles... which totally counteracted bumping it up in the first place... like already said... get a scanner and see if you are getting knock and knock retard... however you can at times get false knock from headers, roller rockers, exhaust leaks near the heads... all types of stuff... only way to see if its real knock or false knock is to throw in some 93 and octane boost, or some 110 octane race gas and see if the knock goes away... if it does then you need to turn the timing back down, cause its real knock... if it doesn't its false knock and you are alright...

 

one other thing i thought i would add...
there is a point where there's too much timing no matter how much fuel you use. Knock will occur when the mixture fires while the cylinder is still on its way up...timing advance is firing the plug this way too...before top dead center, but if you go TOO far before TDC you lose power for obvious reasons...the combustion slow's the pistons speed and is pushing against it while it is going up. The goal is to fire it off early enough that its really hottest when the piston gets to the top, but not so early that the flame is out too early.

 

having more spark wouldn't cause a lean condition would it?

if you have a set amount of air and fuel going in by advancing the timing you are not going to out of nowhere reduce the air. the know is caused by, as you said in your second post, the combustion proccess starts going off to early and sets the pressure back agains the piston before the piston reaches TDC... so you are making the motor work against it self


there are some other things you can try to do though. I would recomend leaving the timing stock since advancing it isn't going to make s<x>hit loads of power. but you can warm the motor up and then srap some water into the TB and in hopes of it breaking up the carbon build. another t rick that I use on my rotary (not sure how it would work for you though) is to turn the motor on let it suck up som ATF/carb cleaner mixture and then shut the motor off right when I think it sux enough in there. this way I don't burn all the shi<x>t out of there and yet I don't over do it and waste the mix.... I let it sit like that for atleast 24 hours then turn it on and let it run for a while. trust me it smokes like a b<x>itch but it seems to work to break up the carbon... WARNING: this last one was taught to me for a rotary though, could work for you car but but not sure if it would or not without causing hydrolock.

other things that can cause knock include a clogged fuel filter, bad plugs/wires, and a few other things that elude my sick a$$ right now


hopefully someone else will help out here


best of luck though

 

Pre-ignition= Mixture ignites before the spark plug fires. Usually from carbon deposits glowing red hot in combustion chamber.

Detonation= Mixture burning way too fast. Usually caused by excessive pressure and heat and/or low octane fuel. A richer mixture will help stop detonation cause it has a cooling effect in the chamber. Retarding timing helps cause the mixture is ignited when piston is closer to TDC. If timing it advanced too far, the mixture starts burning while it's still being compressed. If the press exceeds a certian value, the mixture explodes instead of burning.

 

That is what I was wanting to say, but it didn't come out like that.