Strange acceleration issue

[mhughett]

I've noticed that my car has had the following trait since it was new and wanted to see if others have noticed it on their cars as well.


When I leave work, I exit the parking lot and immediately get on an open road (50-55mph limit) and go about a half mile before I stop to turn. As I am accelerating on this open road, initially the car lacks power. It doesn't sputter or sound bad it just lacks the normal power. However, after about 10-15 seconds it is like a boost kicks in and it is back to normal. Most of the time I am accelerating in third gear when the "boost" kicks in and it is very evident and predictable when it happens. It almost seems like it could be something related to the fuel system but I've never had it checked out. Once this happens, the car runs perfectly and it won't do it again until the next time I leave work. When I come from home I have to go through a bunch of residential streets and I never notice the issue. Only when I just start up and have consistent acceleration from the beginning does this occur.


Anyone have any ideas?

[bababooey]

warmed up properly before mashing the gas?

[cdq85]

I've felt exactly what you felt there a couple times. It's 100% from the vehicle not being warm enough. Not sure what the technical aspect of why it does but I'm pretty sure it's normal

[Joyride86]

What RPMS are you at? At low RPM, you're not in the power band. Once it hits a certain RPM, that's where the power kicks in.

[Tcoat]

Originally Posted by cdq85

I've felt exactly what you felt there a couple times. It's 100% from the vehicle not being warm enough. Not sure what the technical aspect of why it does but I'm pretty sure it's normal

Back in the day (sorry Hum) there was a mechanical choke that would cut air to make a richer mixture for starting and warm up. There was no way on earth you were going fast until the engine heated up and opened that choke (or in the case of several of my cars I pushed the control back in). There was a very perceivable difference when that sucker opened up and leaned out the mix.
New cars do the exact same thing with the air/fuel mix only they do it electronically.

[twag4]

@Tcoat is right. Also, the cam timing doesn't work properly when the engine oil temperature isn't up at least somewhat. This was explained to me by one of our very knowledgeable vendor/gurus from this site. If the car was at or near full operating temperature, none of these things would be an issue. Hopefully, that is all you're experiencing.

[mhughett]

These explanations all make sense and I have no issues if they are considered "normal" for this vehicle. It's just that I've had all sorts of high-performance as well as other sports cars and I've never seen anything like this. It's almost like there is a 15-20 second timer in the engine and it only allows for 50% of normal power and then after the timer goes off, the other 50% kicks in. It isn't a gradual increase in power--it is instantaneous. It occurs at relatively low (3-4k rpms) so it is not like I am thrashing the car when it is not fully warmed up. At lower rpms, it is not nearly as noticeable as generally, you aren't using much power and don't get much torque anyway.


By the way, it has nothing to do with the well-known "flat spot" in the torque curve that we have on these cars around 4-5k rpms. Also, this only occurs on a first start-up and it does it only once. After that, car behaves as it should.

[Tcoat]

Originally Posted by mhughett

These explanations all make sense and I have no issues if they are considered "normal" for this vehicle. It's just that I've had all sorts of high-performance as well as other sports cars and I've never seen anything like this. It's almost like there is a 15-20 second timer in the engine and it only allows for 50% of normal power and then after the timer goes off, the other 50% kicks in. It isn't a gradual increase in power--it is instantaneous. It occurs at relatively low (3-4k rpms) so it is not like I am thrashing the car when it is not fully warmed up. At lower rpms, it is not nearly as noticeable as generally, you aren't using much power and don't get much torque anyway.


By the way, it has nothing to do with the well-known "flat spot" in the torque curve that we have on these cars around 4-5k rpms. Also, this only occurs on a first start-up and it does it only once. After that, car behaves as it should.

See post #5.
It is an immediate change in power. These are "lower" powered than many (most? all other?) performance cars so the change is just more noticeable then it is with them They do it as well you just can't tell.

[BRZSS]

Don't quote me, but I believe the Direct Injection system does not come on right away. It waits a certain period of time before it goes active. One of the tuners would have to confirm that, but I recall reading it a while back during a tuning discussion. Its part of the warm up cycle on the engine. And if thats the case, your only running Port Injection with reduced timing while the car runs a little richer to warm the cat's up on a cold start. Would make perfect sense why your seeing hesitation for a moment. Can't say I've experienced this myself though. But, I let my car sit for about 30 seconds to a minute when I first start it before I drive.

[Tcoat]

Originally Posted by BRZSS

Don't quote me, but I believe the Direct Injection system does not come on right away. It waits a certain period of time before it goes active. One of the tuners would have to confirm that, but I recall reading it a while back during a tuning discussion. Its part of the warm up cycle on the engine. And if thats the case, your only running Port Injection with reduced timing while the car runs a little richer to warm the cat's up on a cold start. Would make perfect sense why your seeing hesitation for a moment. Can't say I've experienced this myself though. But, I let my car sit for about 30 seconds to a minute when I first start it before I drive.

You are 100% correct and may be quoted. That is part of the "electronic" choke system I was talking about.

[Clipdat]

Are you running a tune?

Originally Posted by mhughett

I've noticed that my car has had the following trait since it was new and wanted to see if others have noticed it on their cars as well.


When I leave work, I exit the parking lot and immediately get on an open road (50-55mph limit) and go about a half mile before I stop to turn. As I am accelerating on this open road, initially the car lacks power. It doesn't sputter or sound bad it just lacks the normal power. However, after about 10-15 seconds it is like a boost kicks in and it is back to normal. Most of the time I am accelerating in third gear when the "boost" kicks in and it is very evident and predictable when it happens. It almost seems like it could be something related to the fuel system but I've never had it checked out. Once this happens, the car runs perfectly and it won't do it again until the next time I leave work. When I come from home I have to go through a bunch of residential streets and I never notice the issue. Only when I just start up and have consistent acceleration from the beginning does this occur.


Anyone have any ideas?

[mhughett]

Originally Posted by BRZSS

Don't quote me, but I believe the Direct Injection system does not come on right away. It waits a certain period of time before it goes active. One of the tuners would have to confirm that, but I recall reading it a while back during a tuning discussion. Its part of the warm up cycle on the engine. And if thats the case, your only running Port Injection with reduced timing while the car runs a little richer to warm the cat's up on a cold start. Would make perfect sense why your seeing hesitation for a moment. Can't say I've experienced this myself though. But, I let my car sit for about 30 seconds to a minute when I first start it before I drive.

This is exactly what it feels like and I was wondering the same thing. I am not running any kind of a tune.