Hello, I have a 2002 SS 6spd. I have the 345HP version from SLP, and have added only the SLP loudmouth cat-back. My question is, when decellerating I downshift to slow the car. On occasion the engine will decell normally, then sudenly decell even more, as if it has a "jake brake" !! I really like it when it does this, as it adds more sound to the exhaust, and when it finally comes to a stop, it gets a nice, burble/pop out the exhaust. It also lets me not use the brakes, which cops hate by the way! Anyways, I'm wondering what causes this? Is this due to the air pump? It only seems to act this way once the car is warmed up, and I don't have the A/C on. Which, by the way, ****' me off! Why does the idle remain so high, and the throttle react so slowly when the A/C is on?? My goal would be to get perfect throttle response at all times, but I'm guessing the only way to do so, is removing all the electronic controls, and emissions stuff. So, has anyone felt this?? Thanks in advance!!!

 

I just read on here recently that the engine will go into a different "mode" when it slows down below 1900 rpm I think it was.........or thereabouts?! It was something to the effect that more fuel is still being applied to a certain point, but then once the car senses that the speed (or just the rpm's) are dropping, then more fuel is cut??

....................."please don't quote me on that though?!" What I read was something along those lines though.

In regards to A/C hurting your throttle response?? Well why do you think that guys remove all the belts from the engine for extreme racing?? (ie: A/C, PS, alternator) or simply don't use some of these devices (ie: no A/C, no PS, electric water pump instead of belt driven water pump)........................it's a known fact that the A/C compressor draws a lot of power from the engine, and that's why it's a "luxury" item, and if you don't like the power loss, leave the switch OFF!!

 

Capn Pete, you sure like using smilies a lot, don't you?

 

I know, I get carried away sometimes?!

 

Its a well known fact that a/c robs power, not just on LS1's but most cars. You have t-tops.......use them.

 

To answer the question, what you are describing is a "feature" of the GM programming.

The short version: When you are off the gas and slowing down, the computer waits a specified amount of time, looks for a specified RPM (around 3K), and a specified rate of decelleration (don't know the specifics ) and then it begins to cut back on the fuel flow.

So, it's cutting back on the fuel since you're not using it. It saves gas, and makes a modified exhaust have that great burble sound. I drive with my cutout open all the time, and I love the burble.

 

Thanks for the input guys, but I think some may have been confused to my A/C remark. I do not have a problem with the A/C "robbing" power. Instead, I noticed that while cruising with the A/C on, and pushing in the clutch to shift, the idle remains very high. It will gradually come back down, but it takes a bit. My problem is while cruising with the A/C on, the engine seems to go on it's own, without my throttle input! I realize not using it would be the simple solution, and that's what I already do,... but... there must be a better way! As to the deceleration.. I figured it was some computer controlled thing, but... what affect does a Hypertech, or similar device have on this decell condition??Does anyone have a "chip", or other computer mod, and still have these symptoms?? Thanks...

 

Cutting back the fuel happens, but that happens immediately after you let off the gas. The sound is caused by the fact that the computer retards the timing by a pretty big amount on deceleration. When you are at an rpm above what the computer thinks the idle should be and you let go of the gas, it waits a second or so, and if the rpm did not come down to the specified number, the timing will go from around 40 degrees before TDC to about 10 degrees before TDC. That is what makes your exhaust louder. Just log some data or look at real-time data with Freescan or another program, you can see it happen!

Sam

 

/\
|
|

Yeah ... that too.

As for the Hypertech thing, when I ran their tuning, it did not change this feature.

 

About the A/C revs...when you turn on your A/C, it puts a slight load on the engine (when the condenser pulley kicks in). Therefore, it'd be possible that the car is programmed to idle a couple hundred revs higher to help avoid stalling and/or low, low rpm clutch engagement (almost stalling). Keep in mind the LS1 very well puts out 300+ hp, but that's @ 5000+ RPMs. When you're driving around town, you're not launching off the line with the tach pegged at 5000. At 1000 RPMs, a stock LS1 only has about 50 hp and 200 ft/lbs of torque dragging a 4000 lb skin. So, by idling a little higher on the power curve, the slight load from the A/C is compensated for to assist daily driving.

 

Ahhh...I have always wanted to know why this happens.

Sometimes I decelerate while in gear and the clutch out, and the engine decelerates smoothly and then "drops" to what feels like a lower power level all by itself (without the air on or anything), without touching the clutch, the gas or the stick. This happened on my LT1 and now my LS1.

The explanations above makes all kinds of sense now. Thanks!