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2018 ATS Standard; (RIP) 2004 Sedan Deville
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Discussion Starter #1 (Edited)
Hi all,

I have the 2018 ATS 2.0 RWD. I've noticed that w/ the recent cold weather in NY during the first few minutes of a drive the car behaves almost as if there's fuel restriction and shifts kind of hard into 2nd. This happens when going from a 10mph roll after I hit the accelerator to ~50%.

I do sometimes warm the car up for 5 mins before driving it, but this has no affect on the lag.

After 2-3 mins of driving, this seems to go away.

ALSO, when the vehicle is idling, I sometimes feel a slight shimmy from the engine--almost like a car running an octane too low. (I only run Tier-1 93).

Anyone ever experience any of this ??

It's gonna be going in for it's first oil change at around 6,000 miles in a week or two and I'm wondering if I need to mention this to the dealer...or if they're gonna think I'm crazy.


Thanks!
 

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2014 ATS 3.6 Premium RWD, 2016 Corvette Z06, 2018 GMC Sierra Denali 2500HD Diesel
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2,907 Posts
The 1 to 2 upshift sounds like a common issue with the 8L family of transmissions. My 2016 Z06 has the 8L90 high torque version of the 8L45 in your ATS and to avoid an initial rough 1 to 2 shift while the car is still stationary I manually shift into second and then back into first during the first cold start of the day. The hydraulic clutch pack actuator used in the 1 to 2 shift has an initial slow fill after it fully drains while sitting and manually doing the first shift while the car is at idle allows a pre-fill so that you don't get an initial rough shift that occurs when the clutch packs used for first gear release before the pack for second is fully ready to engage. I have no idea why GM hasn't changed the programming to do a partial fill of the offending actuator at startup, this same problem existed in 2001 when they first started using the Allison 1000 series in their heavy duty pickups and a few months into ownership they issued a software update which did a partial pre-fill at cold start.

You will notice a different operational pattern at cold start. Until fairly recently, cars were allowed to be pretty dirty for several minutes after a cold start but the EPA tightened up cold start emissions requirements so now at cold start the timing will be severely retarded for a short time while the mixture is enriched so that the cats will have raw gas vapor to work with which will heat them up very quickly so that the car can pass the cold start test. After this initial strategy, engine programming is still different until it is at normal operating temperature in order to provide better overall drivability but this strategy to avoid really annoying performance behavior will cause some minor anomalies like the intermittent harsher than usual idle. Transmission programming is also different with shifts to higher gears being slightly delayed and the torque converter lockup clutch engagement will also be delayed until higher road speeds; these strategies reduce the load on a cold engine and also help it to warm up more quickly by allowing the engine to run at higher RPM and using the heat generated in an open converter to also add heat to the engine coolant (there is a fluid to coolant heat exchanger in the radiator tank).

Many current engines will not idle as smoothly as older engines, direct injection tends to work against a really smooth idle and there has been some move back to using a combination of port and direct injection to smooth the idle and provide intake valve cleaning with some manufacturers. GM uses a combination of direct and port injection in the new LT5 engine used in the Corvette ZR1 but that is purely because the direct injection system can't flow enough fuel to meet the engine's maximum power rating and this engine runs direct injection only from idle up to near rated power before the port injection system also comes into play.

They won't think you are crazy BUT it probably is normal for this setup and even if it weren't the odds of you getting some form of the "no CEL, no problem" response are very high.

And letting the car idle to warm up is about the worst thing you can do for a cold engine. Let it run a few seconds to get the fluids moving and drop off from the fastest part of the cold start idle and then drive it at moderate load, moderate speed to finish warming it up. It takes a very long time to warm up an engine with no load and a lot of wear along with oil dilution occurs under these conditions. You don't want to run it at full load/RPM until temperature is near normal but part throttle is good. My 2016 Corvette at cold start displays a red line at 3,500 RPM that gradually moves up to the rated 6,600 RPM as the engine comes up to normal temperature. I still will not run it at high throttle until the oil temperature comes up to normal but it is a dry sump engine with a 10 quart oil reservoir so the oil doesn't heat up as rapidly as a normal wet sump engine and with the ATS once the engine comes up to normal the oil is close behind. I wish GM gas vehicles had a warm-up strategy like their heavy duty pickup diesel. When it is 32 or below ambient the pickup starts at its normal 650 idle in park and then gradually ramps up to 1,200 RPM and the transmission is engaged with the output shaft locked so that the torque converter puts a significant load on the engine. The variable exhaust vanes on the turbo also go to their closed position to help heat the engine and this cold start strategy provides a nice warm-up under load. Driving moderately is still the best but this loaded cold idle is far better for an engine than the unloaded cold idle in a car.
 

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'14 ATS 2.0T 6MT
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464 Posts
Agreed, all emissions related. I have a 6MT and my wife has a cruze 1.8 6MT. Both exhibit goofy throttle response when cold... They both also run pig rich during this time so ya, not a DI issue just the tune.
 

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2018 ATS Standard; (RIP) 2004 Sedan Deville
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206 Posts
Discussion Starter #4
Thank you for such a detailed reply--there are so many knowledgeable folks on here!

I am going to try to shift to 2 and then back to 1 while in park and then shift to D and drive it to see if this strategy works.

I never get on the accelerator of a car until it is fully warmed up. That said, the only reason I am "warming up the car" is because mine came with the remote start feature and I hate wearing a jacket in the car...but if not doing this improves the longevity of the engine (components, thereof) I can deal with a jacket for my 10 minute commute to work.

When the lease is up I may consider buying this thing and seeing if I can get it to 200,000 mi. but we'll see!
 

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2013 ATS 3.6 Premium RWD
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363 Posts
Anyone run a heater block on these cars? That might part these issue, plus hopefully less cold start wear.
 

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2013 ATS 2.0T Lux AWD Black Raven
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Lol, shortly after I bought my ATS I started it on a cold morning and my wife, standing near the car, said "do you know there is black smoke coming out of the exhaust pipes?"
 

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2014 ATS 3.6 Premium RWD, 2016 Corvette Z06, 2018 GMC Sierra Denali 2500HD Diesel
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On the C7 Corvette forum a number of people want to know how to keep that loud startup idle going so the EPA regulations do have some unintended benefits. With the dual mode exhaust in track mode the Z06 startup bark and initial idle will rattle garage doors but it quiets down after about 30 seconds much to the dislike of some owners. It is fun to remote start it when cold while an unsuspecting friend is near the back of the car :)

Part of the cold shift strategy is to warm up the engine more quickly in order to provide faster heat to the cabin. Prior to my 2008 CTS, I could leave the climate control in auto with my GM vehicles and the blower didn't come on until there was sufficient coolant heat but with the 2008 CTS I had to remember to shut it off when pulling into the garage for the evening. When I bought the CTS my daughter was still very young and the HVAC would start blowing icy air at full blower speed right after starting the car while I was strapping her in the car seat and when it is already cold I didn't need GM adding to the wind chill.
 

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2018 ATS Standard; (RIP) 2004 Sedan Deville
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Discussion Starter #8
Let's back up for a second here: Is it bad for the car/engine to warm it up for 2-3 minutes prior to driving in cold weather? If so how and why is it bad?
 

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Prev: 2018 ATS 2.0T NOW: 2020 CT4-V JR
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Other than a stutter 1 to 2 shift when cold, and it did that in the summer, I haven't seen any cold driving issues with my ATS.

I very seldom use remote start, but it seems to me that a 3 minute warmup could be better than putting a strain on a cold engine
by driving it right away and having to gun it to get out of your street, while it's not warmed up. I admit that I don't worry about
longevity past the warranty and I don't drive a lot of miles. I use premium gas.
 

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2014 ATS 3.6 Premium RWD, 2016 Corvette Z06, 2018 GMC Sierra Denali 2500HD Diesel
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Any extended cold idling isn't good for an engine because any warm-up occurs very slowly while creating fuel wash-down of the cylinder walls and dilution of the oil. Part of the OLM calibration extracts a big penalty in calculated oil life based upon extensive cold idling and frequent short trips in cold weather.

Basically, you want your cold engine to run at idle just long enough for it to stabilize and then drive it with moderate load. You don't want to immediately go to high throttle/high RPM operation and if you live on a fast (55 MPH), busy street that isn't optimal but pulling out into typical residential 30-35 MPH traffic provides perfect warm-up conditions. I am in a rural area with 55 MPH limits/ 63+ typical but traffic is light and I am typically up to around 55 before braking for the first stop sign 2.5 miles away; the engine never has to go over 3,000 RPM during this segment and is well below this for the first mile or so. When traveling, especially with my pickup which is diesel powered with a slow warming engine, I will drive it for a couple of miles around town before hitting the interstate on-ramp with its high merge speed. To my knowledge, modern vehicles aren't doing any specific power or RPM limit during cold operation other than the normal operational changes and emissions required programming, my 2016 Z06 has recommended RPM limits shown on the tach during warmup but it still has the same 6,600 RPM fuel shutoff when cold or warm. Back in the days before fuel injection some makers of 4 barrel carburetors locked out the large secondaries during initial vehicle operation as specified by the engine manufacturer to prevent excess loading of a cold engine.

I use remote start a lot on my vehicles for convenience but I start it as I am walking up to the vehicle. By the time I am belted in, maybe 30 seconds after hitting remote start, the car/truck is ready to go.

A block heater does help and if I lived on a busy street that required hard acceleration to high speed I would use one. When I was growing up on the coast a friend's father was the chief engineer at a TV broadcast station transmitter site and one of his responsibilities was maintaining the large emergency backup generator. The prime mover for the genset was a big Detroit Diesel engine and its cooling system was plumbed into the liquid cooling system for the high power transmitter tubes which kept the engine block and lubricant at normal operating temperature 24/7. When the power failed engine air starter engaged and the transmitter was running at full power off the generator in a couple of seconds after power failure courtesy of an engine that was already ready to go. Some of the larger home standby generators have an automatically controlled block heater so that they can better take the load during switchover during cold weather.

There are many articles written within and outside of the automotive industry as to why extended cold idling is bad, here is a recent one citing an engineer from Argonne National lab (they are more the defense applications side compared to their sister Fermi lab which is more pure academic research driven): https://www.popularmechanics.com/cars/a19086/warming-up-your-car-in-the-cold-just-harms-engine/
 
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