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Struggling at light throttle / TC issue

 
Old 01-04-2019, 10:33 AM
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Rockstar_Andy
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Default Struggling at light throttle / TC issue

The reality of where I live and work is that I'm stuck in light throttle traffic or not on the highway as often as I would like with the car but I'm noticing it has felt pretty bad when it comes to driving lately, and unfortunately I'm not much of a gear head when trying to figure out why.

The only way I can describe it is at light throttle it feels like the car is struggling. It almost feels like it just wants me to blow out a ball of air out the exhaust or something like a pressure buildup that I am convincing myself I feel through the accelerator pedal on light throttle. The car kind of lurches forward like it's looking over a ledge as it struggles to initially accelerate and then it finally begins to accelerate. I also feel like the car is not as fast in acceleration as it was initially unless I have a wide open throttle, even then it feels rough at times.

Now I have the torque converter issue (rumble strip feeling) that most A8's have and I can replicate it on command with light throttle input at certain ranges of MPH. I've gone through the rigmarole with the dealership of "we can't replicate" to "transmission fluid flush" next time, to them telling me when I got an oil change in December that Chevy has a "new answer" for this that they are supposedly enacting in January and scheduled me for then. (I was told it is a 'special tool' a new fluid formula and whatever else the PPD asks for.....I am reluctant to believe this is truly a fix for a mechanical part issue but, who knows.)

I don't know if these are related symptoms to the TC issue or an entirely different issue itself?
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Old 01-10-2019, 03:27 PM
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Gearhead Jim
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Hard for me to tell if your problems are related. A good dealer (there are some good ones) should be able to sort it out for you.

The new fluid and associated procedure is just arriving at some dealers, your own dealer should be able to get the descriptive bulletin and fluid "soon". Someone will likely post the new bulletin in C7 General soon. The last version was dated October 11, 2018; and is obsolete.

Throttle response is dumbed down somewhat when you have the car in Tour or Weather, putting it Sport will not give any higher total power but will make the throttle more sensitive at partial settings, which I prefer.

Good luck!
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Old 01-11-2019, 09:44 AM
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Yeah I pretty much leave it in Sport mode the entire time unless I'm on cruise control on the highway then adjust it to Touring or Eco.

They have me scheduled for the 22nd for the torque converter resolution and I hope it works but I'm skeptical about a fluid fixing a mechanical issue. Or am I wrong on that?

It's like a lurching/sucking in air issue. Feels like the car is gasping until a wide open throttle is given. Hard to describe but definatley a horrible drive feel. I'll bring it up and see what they say at the TC appointment but it is frustrating to not enjoy driving a car that is meant to be enjoyed.
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Old 03-06-2019, 11:04 AM
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Originally Posted by Rockstar_Andy View Post
The reality of where I live and work is that I'm stuck in light throttle traffic or not on the highway as often as I would like with the car but I'm noticing it has felt pretty bad when it comes to driving lately, and unfortunately I'm not much of a gear head when trying to figure out why.

The only way I can describe it is at light throttle it feels like the car is struggling. It almost feels like it just wants me to blow out a ball of air out the exhaust or something like a pressure buildup that I am convincing myself I feel through the accelerator pedal on light throttle. The car kind of lurches forward like it's looking over a ledge as it struggles to initially accelerate and then it finally begins to accelerate. I also feel like the car is not as fast in acceleration as it was initially unless I have a wide open throttle, even then it feels rough at times.

Now I have the torque converter issue (rumble strip feeling) that most A8's have and I can replicate it on command with light throttle input at certain ranges of MPH. I've gone through the rigmarole with the dealership of "we can't replicate" to "transmission fluid flush" next time, to them telling me when I got an oil change in December that Chevy has a "new answer" for this that they are supposedly enacting in January and scheduled me for then. (I was told it is a 'special tool' a new fluid formula and whatever else the PPD asks for.....I am reluctant to believe this is truly a fix for a mechanical part issue but, who knows.)

I don't know if these are related symptoms to the TC issue or an entirely different issue itself?
Andy, I can completely relate to that feeling. Basically, our C7's were designed to be very economic at part throttle (1.2 g/sec-deg throttle MAF response, this is a meager airflow rate/power you feel is not enough) and a track car at 1/2-full throttle (10 g/sec-deg throttle MAF response, "the lurch after the ledge"). It is very unpredictable. Visit our technical page for a better explanation. https://www.solerengineering.com/technical

I've added a picture of the OEM throttle body here in your own terms, not bad for a non-car person. You nailed it IMO.

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Last edited by [email protected]; 03-06-2019 at 11:22 AM. Reason: added pic
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Old 03-12-2019, 06:31 PM
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They all do this stock.There are a couple companies that make a dial up throttle that makes it mild to wild.
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Old 03-15-2019, 08:39 PM
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Are you sure this illustration is accurate?

it seems there is no airflow until the blade is over 30 degrees.
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Old 03-15-2019, 08:48 PM
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Originally Posted by RussM05 View Post
Are you sure this illustration is accurate?

it seems there is no airflow until the blade is over 30 degrees.
Exactly, that is the OEM design. It is choked until that point. From idle up to 30 deg mass air flow increases at a meager rate of ~1.2 g/s-deg. Check our SE8223-100 Modified Throttle Body.
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Old 03-16-2019, 09:07 AM
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I don’t agree with your analysis exactly as you stated above. It’s not chocked. It’s controlled at low throttle operation as it should be. I started a thread about this subject a couple of years ago and posted photos of both the stock and ported throttle bodies. See: https://www.corvetteforum.com/forums...post1592298998

To give the throttle a smooth response as you come off of idle, the GM engineers restricted air flow for the first ~20 degrees. The helps when you are pulling out the garage or around a parking lot.

I ported my throttle body and in the process totally removed the upper lip. Wrong thing to do as the amount of air delivery increase so dramatically off idle, the ECU pulled timing by 15 degrees. Then when RPM reached ~2800, the timing jumped instantly back to normal and the engine surged. The ECU monitors manifold vacuum and pulled timing assuming the engine was under load to prevent knock when you remove enough material in that throttle range.

From my experience, a ported throttle can lead to low speed drivability issues.

I scrapped that throttle body and bought one from Katech. Their first version and it also removed the upper lip. Same problem. I emailed Katech and explained what I had observed on my HP Tuners scan. They asked me to return it and was sent a new one which the upper lip was almost untouched. The car drove smoother and timing wasn’t being pulled. I still have the Katech ported throttle body on the car. But the stock throttle body is good.

in my view, the GM throttle body is a good design as-is to give good control as it comes off idle with this very powerful engine at low RPM.

Last edited by RussM05; 03-16-2019 at 09:22 AM.
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Old 03-16-2019, 10:47 AM
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I agree Russ, the OEM is a good design according to their goal. It shall fit many models (Trucks, SUV's, Cadies, Camaros), it should be fuel efficient at low to part throttle, and very aggressive at say >40% throttle. That is what they marketed, a track star that does nearly 30 mpg on the Hwy...and they truly did it.

It is choked, very, very choked. Measure/monitor your manifold pressure at part throttle, compare it to your local ambient pressure and you will see for yourself. The most important part is not that, it is the MAF rate of increase ~1.2 g/s-deg, monitor that and see results for yourself, you will land near that number at part throttle.

Completely removing the upper lip is a step too far to fix the problem. There is a certain amount that is adequate.

Yes, some PTB's can lead to low throttle drivability issues, we found that on four different brands of those, this is exactly why we designed our own.

If your taste and goals align w/ those of the OEM design, there is nothing wrong w/ that. I just wanted to offer a solution to the OP, who is concerned about "struggling at low throttle".
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Last edited by [email protected]; 03-16-2019 at 12:03 PM.
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Old 03-16-2019, 02:38 PM
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My 2016 C7 Z06 A8 with an AFE CAI and Tony Mano TB has always run like a top, smooth and fast.
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