car pulling timing below 1500 rpm
 

My car pulls timing under 1500 rpms in closed loop only. Would an lt4 knock module take care of this? I hve been chasing this problem for the last couple of weeks. My car currently won't pass the im240 emissions test. The test is almost exclusively conducted under 2000rpms. I have adjusted the rockers to stock speck 3/4 turn past zero lash in an effort to minimize noise. But it still pulls timing as much as 10 degrees sometimes.
Any thoughts would be helpful.
Thanks,
Kory

This will happen almost all the time if the throttle position changes quickly at those rpms, like if you try to give it a good amount of throttle under 1500 rpm.

If it pulls timing while the throttle is held stready in a cruising type situation, then you have a problem, and a LT4 KM would be a very good idea to help diagnose the issue.

Dan

Thanks for the reply. Do you happen to know a good place to get one?
Thanks again.
Kory

I got mine from gmpartsdirect.com

Dan

If this is happening in closed loop only, i would be suspicious of the problem being acutal knock.

In open loop you run a slightly richer afr than stoch. which can reduce detonation. You might try a tank of race gas to see if the kr is reduced or goes away.

Also, what gear is the KR happening in? KR while lugging the engine in a high gear/low rpm is pretty normal.

Good point.... the LT4 KM is not the cure-all for every knock problem. It is useful to filter the noise from the Crane Gold roller rockers used in the factory
LT4 engine. That's specifically what the module was designed for. Its ability to filter out exhaust noise or other extraneous mechanical noise is open to debate. To ascribe some sort of magical knock elimination properties to it is not realistic.

What part of the emissions test won't pass - CO, HC or NOx? How close are you to the allowable? Posting the actual results might help point you in the correct direction.

The first step in addressing knock retard is to identify the specific conditions that produce it. Shifting with lifting throttle can easilly produce knock retard. Lugging the engine, as described in the post above, is a common cause of knock, particularly if you have deleted the EGR system. EXACTLY when, in closed loop under 1500 RPM do you get knock retard? How much? Is the throttle steady or moving up or down? Do you get any knock retard under any other conditions?

Then try the high octane unleaded fuel. If that cures it, you know its real. If it doesn't its probably "false". Start looking for mechanical noises - loose/worn motor mounts can be a serious problem, since the knock sensor is right next to the motor mount. Look for signs of a high voltage wire too close to the knock sensor harness wire. Induced cyclic voltages will be seen as "noise",