Can someone please explain to me what it means by the timing being pulled ? Why does it have an effect on the car's power ? I don't need an indepth explanation just please help me understand.

 

Timing is when the spark plug fires in respect to the position of the crankshaft (and therefore the piston). In order to get complete burn, the spark plug is fired before the piston reaches the top of the compression stroke. In the old days the distributor did this job with a set of points. There was also a set of weights that flew out the faster the distributor spun and this actually moved the plate the points was mounted to and thus giving more timing (fired the plug further and further before top dead center) the faster the engine spun. There was also a vacuum advance that allowed more timing at part throttle.

In the old days a small block chevy liked something like 36 degrees of total timing (number of degrees of the crankshaft rotation before the piston hits absolute top dead center). However, the LS1, LS2, LS3, and LS7 can't run that much timing. Most people run around 20 degrees of total timing at wide open throttle. If you run more than that, the burn happens too fast and explodes (you hear pinging). If you run a higher octane fuel (actually slower burning fuel), then you can run more timing and make a little more power.

On our cars, the computer takes care of how much timing the engine has. There is also no distributor since each spark plug has it's own coil.

Sorry for all the info,
Glenn

 

VERY WELL STATED

 

The LS engines are very efficient and don't require a lot of timing to make power.

The term timing being pulled, refers to the ECU removing timing due to detonation, saving the engine from damage.

 

Thank you very much. No need to be sorry it was exactly what I was looking for.

 

Thanks.. So does a "tune" adjust the amount of timing that's being removed ?

 

I just had mine tuned and the tuner changed the timing tables so that I had less timing. That was because I was getting Knock Retard (KR). The problem when you get knock retard is that the computer pulls timing and even after the knocking (pinging) subsides, it takes some time before the computer quits pulling the timing. So if you can reset the timing tables so that you don't get any knock retard, the engine actually will make more power than if you have more aggressive timing but the computer is always pulling timing because of knocking.

I was getting up to 8 degrees of KR when I scanned my car. Sometimes headers or rattles can cause something called false knock. The way to check this out is what I did. Go get some 100 octane fuel. I mixed it so that I had 95 octane in my tank. I did the scans again and sure enough the KR went away. That told me it was real knock and not some rattle or false knock.

The last problem is that even though Chevy says the engine is fine on 91 octane, it really likes 93 octane a lot better. We are stuck with 91 out here in the West. So you have two good choices. Retune your computer so that it runs fine on 91 or add Torco to get your octane up to 93 to 94.

 

The ecm also pulls tiimng if the intake air temp is over 87 degrees.

 

Timing is pulled or added during tuning. The engine actually "listens" for knock or ping as this is actually audible. The sound indicates something is wrong. Either the fuel has too low in octane rating and is flashing faster than it should and expanding while the piston is still moving up to finish compressing the fuel mixture or the fuel is fine but the timing is too much BEFORE the piston is ready and at full compress (there is always some advanced time as it needs a little time to light off the fuel) and then the expanding fuel pushes the piston down. If the timing is correct, the push happens smoothly. If the timing is too soon it causes a push from the burning expanding fuel down on the upcoming piston thus the term "knock". When the knock sensors hear knock the sensors tell the pcm that the piston is being hurt by the early firing and the pcm pulls timing so the firing happens later in the compression stroke and stops the "noise" or "knock". Pulling timing limits or reduces the power in the engine.

 

My '05 C6 (4 spd auto, 15k miles) knocks under hard acceleration during cool conditions, say 60F and below. I find when the temperature is higher I do not hear the knocking. I only use Shell, Chevron or BP premium grade fuel (93 in Atlanta). Is the protection provided by the engine management system sufficient to prevent damage (by pulling timing only after it senses the knocking); is this kind of knock too little to cause concern or should I preferably have the engine retuned? I am not keen on losing power. Any advice will be appreciated. It will also be interesting to hear whether other owners experience knocking due to cold air. I find it awkward, but my son hears the same.

 

We had a 60-130 local event, driving there I noticed knocking on a couple of pedal mashes. I was concerned because of the event I didnt want the knock to be present. As it turns out the car ran fine. Great weather, high 70's

So did the ECM "pull" the timing for me and the "knock"went away?

 

Great explanation but just to correct one thing.....The vacuum advance moved the breaker plate (points). The centrifugal advance (weights) moved the rotor in relation to the distributor shaft.