ThreadHijacker

Hooked up a scanner to the 2012 jk today because I had it out. Some interesting things:

During a half-hour drive the timing advance was as follows:

idle -- 12°
45-55 mph coasting with foot off throttle -- 20-30°

The odd thing is when you push the throttle slightly while coasting the timing jumps up to 50° and push it more it jumps back to 20-30*° and 5-15° on heavier throttle. It seems like there is a spot in the throttle position where the timing really advances and if you back off completely or give it more throttle the timing retards. Does this seem normal to any expert tuners or mechanics? I wonder if that much advance at light throttle could contribute to ping.

I'm not trying to start any wild theory threads. I just thought the timing advance seemed really high. The other thing I noticed is that some people say the pentastar runs much hotter yet the coolant temp was 199-200° while moving and it hit 220° sitting still. I think the TJ 4.0 ran about the same temp. 210-215°.

Freewill

Nice observation.

I used to spend countless and insane hours calibrating carb, distributor, and cam combinations to get the result I was after. Likewise, without getting into any such debates, it would have been nice if I could have tried that advance curve when trying to get an engine to make a nice smooth and clean transition from trailing throttle to throttle-on.

Edit: Likewise, the computer curve you saw for getting off the throttle would help the emissions and make little difference to the driver. All the advance numbers seem right.

ThreadHijacker

Yeah I thought 50 seemed really high though. I understand why they say some spark knock will happen at lower RPM's now.

Freewill

With engines running so lean and clean, pre-detonation (knock) happens easily. It should never last longer than it takes for the knock sensor to tell the computer to dial back the advance. When a knock sensor doesn't do its job, the engine will detonate loudly and often. Sometimes a combination of bad fuel and high temperatures can outrun the computer's ability to manage knock.

Dale_K

My 2012 pings going up steep hills and your observation confirms something I;ve noticed. If I go up a steep hill with curves that keep me at a moderate throttle I get pinging. On an equally steep hill that's straight I can bury the throttle and there's no pinging even though it's at the same rpm as the other hill. My 2012 manual trans doesn't like 30% throttle up a hill at 2,200 rpm (3:73 gears). I drive my Chevy Cruze manual trans about the same and it doesn't ping going up the same hills. I can adjust my driving in the Wrangler to keep the rpms about 2,500 and make the pinging stop. I wish I could test an automatic up the same hill to see what gear/rpm it would use.

ThreadHijacker

Under heavy load it does always seem to come down so I guess that's what is really important.