When driving home, I have to go down a hill and so I go down it on 4th gear to keep my speed down. I noticed something that is strange. When I put the car in 4th and begin going down the hill, the car will speed up. Once the RPM's hit 1900, it's like a brake comes on. The car doesn't speed up anymore. Also when it reaches 1900 there is the slightest jerk, you can barely feel it so it's not anything to worry about. Also when it hit 1900 RPM's, the engine tone slightly changes.

I was just wondering if anyone else noticed this and is it anything to be worried about...

Thanks

 

Mine does the same thing. Then if you just slightly nudge the gas pedal, it looses the 'braking' and let's the engine rev back up for about 5 seconds. I know what it is now though.

It's the short term fuel trim. I figured it out with my predator. I dped up to 35 in 2nd and let the car coast down while watching the fuel trim stats in real time monitoring mode. When you let off the gas, the injectores still feed a bit of fuel. I assume this is to keep the cats cooled off with a bit of extra fuel. As soon as the STFT readout changes to 0 the 'braking' feeling kicks in.

Now you know.

Or at least now you know what I think anyway.

 

This is a "feature", built into the stock programming.

GM put this there to conserve fuel. If you're driving along, and the let off the gas to use engine braking, the computer recognizes this after a few seconds, and cuts the fuel flow to the injectors since it's just getting wasted. But, the slightest nudge of the gas pedal and your injectors receive their full flow amount immediately.

It's actually a pretty slick system when you think about it.