Is there anything peculiar or unusual with the performance or the drivability of the LS4. Can you feel the engine switching from 4 cylinder to 8 cylinder? And when this happens how does it affect the transmission?

 

Should only happen under low-load situation and highway. The biggest problem is that a lot of the LS4 oil consumption occurs during that switch on cars that suffer from that problem. Often when DOD switches On/Off a puff of smoke comes and you can tell oil is getting by.

Also if you change up the exhaust on the car, it might start to sound like a helicopter when it goes into 4-cyl mode.

Luckily, it's a very easy thing to tune out and turn off.

 

On a completely stock car, its very seamless. Id bet most any non-car person would never even pick it up unless you told them about it and they specifically kept an eye out.

You can definitely tell when it happens if you're familiar with the car as it changes over fairly quickly after you've completed acceleration and hit a steady throttle / low load situation. The engine sound definitely changes a bit and feels a bit different, but after driving for a few weeks you won't even think about it happening.

I don't think it does anything with the transmission. If I remember correctly, it doesn't engage until its done shifting and at a steady state for the speed you're going. The throttle % to disengage it is very low, so almost any notable throttle (to the point where the car would even consider downshifting) and it goes back to all 8 right away.

I agree with Chibi on the exhaust if you change it from stock. I ran an electric cutout on my GP GXP. The exhaust sound in 4 cylinder mode was terrible. The gaps between firing cylinders are notable and causes that "Huey coming in for a landing" kind of sound. I couldn't cruise on the highway with the cutout open as that thumping sound would give you a headache real quick - but admittedly a dumped cutout is the worst scenario for that situation.

If it bothers you at all, just find a local tuning shop to shut it off. Its easy to do. I never bothered as it didn't really bug me.

 

👍 thanks

 

Thanks for the responses - here’s what I’ve noticed - slowing down at approximately 25-20 mph I feel a slight vibration then it goes away - this only occurs when slowing down. Would this be something in the engine program or something transmission? I just bought this car so I’m still learning about it- I’m going to try several different stuff and make notes.

 

Hard to tell just from that description, could also be something in the brakes. Are you coasting, or hitting the brakes when that happens?

 

I forgot to add the brakes have been inspected, a new tie rod and alignment done. Yes on coasting to a stop and it occurs more like less than 20 mph - occurs with the brakes applied or coasting. Going to try something else tomorrow.

 

If you are fairly confident its a powertrain issue, I'd hook up a scan tool to see what the engine data shows. That would help you fairly quickly rule that in or out as a possibility.

I'll say it doesn't sound like one to me either, but I also struggle to come up with an explanation given the stuff you've had done already to the suspension/ brakes.

It is admittedly tough to diagnose stuff like that remotely though.

 

Thanks - I noticed that if I put it in neutral as I come to a stop the vibration doesn’t happen, so it’s obvious it’s a transmission issue or it’s just the way it is. Sooooo??

 

Does the car have poly inserts in the top engine mounts?