Having problems going from engine brake to accelerate

Synchros shot? Weird noises while shifting? Not sure what needs to be replaced?
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Having problems going from engine brake to accelerate

Postby bk7794 » Sun Jul 22, 2012 9:53 pm

I am having major issues with for a while going from engine braking to something like acceleration or even just a little bit of gas. It is really bad in second gear when I am fully linked up and go to accelerate I get some major bucking with some clunking going. I am wondering if the bucking would be less pronounced if the front motor mount would be replaced. And the acceleration to engine braking aswell.
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Re: Having problems going from engine brake to accelerate

Postby fr4n » Tue Jul 24, 2012 12:38 am

no it doesnt harm anything. try flooring it to 8000 rpm in 2nd then suddenly foot off throttle because the street you thought was empty wasnt empty after all...

head through windscreen, seatbelt through ribs and i havent even touched the brakes

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Re: Having problems going from engine brake to accelerate

Postby theholycow » Tue Jul 24, 2012 7:06 am

I'm surprised there was so little response in this thread. I can think of a few users I expected to post.

If your motor mount is messed up then yes, that would almost certainly magnify the clunk.
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Re: Having problems going from engine brake to accelerate

Postby RITmusic2k » Tue Jul 24, 2012 11:43 am

Even with a bad motor mount, going even smoother (and yes, 'even smoother' is almost always possible) on your throttle input can minimize the jerkiness. The tradeoff is that it takes slightly longer to do so.

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Re: Having problems going from engine brake to accelerate

Postby bk7794 » Fri Jul 27, 2012 9:36 pm

fr4n wrote:no it doesnt harm anything. try flooring it to 8000 rpm in 2nd then suddenly foot off throttle because the street you thought was empty wasnt empty after all...

head through windscreen, seatbelt through ribs and i havent even touched the brakes

I didn't think it really harmed anything. It is just annoying...and hard to get smooth. Then my passengers think I don't know how to drive. It usually happens in second gear.

You have a honda?

theholycow wrote:I'm surprised there was so little response in this thread. I can think of a few users I expected to post.

If your motor mount is messed up then yes, that would almost certainly magnify the clunk.
I was hoping it would magnift everything. It is strange..and very irritating. Its whenever I put my foot on the gas usually in second gear. It is all hooked up it just lurches twice...

RITmusic2k wrote:Even with a bad motor mount, going even smoother (and yes, 'even smoother' is almost always possible) on your throttle input can minimize the jerkiness. The tradeoff is that it takes slightly longer to do so.
Of course but by then I might aswell put it in third gear and give it more gas. That is usually what I have been doing. I am wondering if its either the gear ratios or the transmission itself..
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Re: Having problems going from engine brake to accelerate

Postby SonicHKS » Fri Aug 31, 2012 11:01 pm

That's throttle response combined with the mechanical connection that a clutch gives you. When you let off the gas at higher (usually 1800+) RPMs it cuts fuel, a feature called DFCO. When you get back on the throttle you have that sudden application of power. That, and 1st and 2nd gear in which the engine has the least load on it, contributes to it bucking violently. The most you can do is make sure the engine is secure and try to be more delicate when you get back on the throttle. I also meant to say that it can also be a MAF/TPS or even IAC issue.

As said earlier in the thread, a bad motor mount will make that much worse, if you know its bad you should replace it.


THC, maybe you can answer this since you seem to think you know everything. My Sonic seems to barely engine-brake, if at all. Does that mean it doesn't have DFCO and its actually supplying fuel on decel at higher RPMs?

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Re: Having problems going from engine brake to accelerate

Postby Shadow » Fri Aug 31, 2012 11:06 pm

Without even looking it up, I can pretty much guarantee you that the Sonic cuts fuel on deceleration. It's a modern economy car, so there's no way they wouldn't incorporate a fuel cut-off on that car.

I know that the Cruze has three overdrive gears, so I'm pretty sure your car has three overdrive gears too. That's probably the biggest reason that you don't feel much engine braking, especially in the top three gears. Combine that gearing with a small engine and it doesn't surprise me that there's not much in the way of engine braking.
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Re: Having problems going from engine brake to accelerate

Postby Shadow » Fri Aug 31, 2012 11:09 pm

Forgot to say--if you have access to a basic scan tool, you can check the injector pulse and see what it does while you're decelerating. That's probably the quickest and easiest way to know for sure if a car has DFCO.
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Re: Having problems going from engine brake to accelerate

Postby SonicHKS » Fri Aug 31, 2012 11:59 pm

Shadow wrote:Without even looking it up, I can pretty much guarantee you that the Sonic cuts fuel on deceleration. It's a modern economy car, so there's no way they wouldn't incorporate a fuel cut-off on that car.

I know that the Cruze has three overdrive gears, so I'm pretty sure your car has three overdrive gears too. That's probably the biggest reason that you don't feel much engine braking, especially in the top three gears. Combine that gearing with a small engine and it doesn't surprise me that there's not much in the way of engine braking.



I'm talking about engine braking at 3500-4000 in 2nd or 3rd. In fact today I engine-braked at 4500-5000 in it for the first time, and it wouldn't slow down the car at all. Its the first manual car I've driven that drives like this.

I have a BT OBDII scanner that works with my droid, but I don't really trust it. It doesn't seem to interpret boost/vacuum or throttle % correctly so I've just used it as a rough guide.

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Re: Having problems going from engine brake to accelerate

Postby Shadow » Sat Sep 01, 2012 12:52 am

SonicHKS wrote:
I'm talking about engine braking at 3500-4000 in 2nd or 3rd. In fact today I engine-braked at 4500-5000 in it for the first time, and it wouldn't slow down the car at all. Its the first manual car I've driven that drives like this.

I have a BT OBDII scanner that works with my droid, but I don't really trust it. It doesn't seem to interpret boost/vacuum or throttle % correctly so I've just used it as a rough guide.


I've never driven a manual trans car that didn't have some amount of engine braking when I was completely off the throttle and still in gear. The only time I've ever experienced a manual trans car maintain its speed in gear (with no throttle) is going down a steep hill in top gear. I've actually gained speed at times in those situations. Other than that, I'd say that my cars always have some degree of engine braking. So you're saying that if you're in 2nd gear at 4000 rpm and you let off the gas, you'll get no engine braking? I find that very hard to believe. Just to be clear, I'm not calling you a liar, I'm just saying that seems almost impossible to happen. Does your car have an extreme amount of rev hang? How fast does the rpm drop in that situation? I'm sure that you realize that your speed is directly proportional to your rpm (given that we're talking about just 2nd gear here), so the car will slow down as the revs fall. If what you're saying is true, then there would be no difference in the rate of deceleration if you were to bring the car up to 4000 rpm in 2nd gear and let off the gas or if you were to bring the car up to 4000 rpm in 2nd gear and pop the trans into neutral.
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Re: Having problems going from engine brake to accelerate

Postby theholycow » Sat Sep 01, 2012 6:59 am

SonicHKS wrote:THC, maybe you can answer this since you seem to think you know everything.

:lol:
My Sonic seems to barely engine-brake, if at all. Does that mean it doesn't have DFCO and its actually supplying fuel on decel at higher RPMs?

Textbook case of rev hang. How long have you waited for engine braking to begin?

Could also be a feature to prevent loss of traction from engine braking. VW reportedly had something like that, although my rev hang did not match up with the description of that feature.

Side note:
DFCO is not as simple as people like to think. There's a million variables used as excuses not to DFCO.
Shadow wrote:Forgot to say--if you have access to a basic scan tool, you can check the injector pulse and see what it does while you're decelerating. That's probably the quickest and easiest way to know for sure if a car has DFCO.

Which "basic" scan tools can provide injector pulse width? It's not part of generic OBDII data, so it either has to be guessed from other variables (as the ScanGauge II does) or measured by a tool that has access to manufacturer-specific data.

SonicHKS wrote:I have a BT OBDII scanner that works with my droid, but I don't really trust it. It doesn't seem to interpret boost/vacuum or throttle % correctly so I've just used it as a rough guide.

What makes you think it's inaccurate? Keeping in mind that TPS is not going to match, or even be vaguely related to, accelerator pedal position...
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Re: Having problems going from engine brake to accelerate

Postby Shadow » Sat Sep 01, 2012 10:02 am

theholycow wrote:Which "basic" scan tools can provide injector pulse width? It's not part of generic OBDII data, so it either has to be guessed from other variables (as the ScanGauge II does) or measured by a tool that has access to manufacturer-specific data.



Sure it can. Even my old OTC Mindreader (which is a cheap scan tool that is more than 10 years old) can read injector pulse width. You don't need a manufacturer-specific scan tool to see pulse width on OBDII cars, at least not on most cars.

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Re: Having problems going from engine brake to accelerate

Postby SonicHKS » Sat Sep 01, 2012 3:45 pm

theholycow wrote:
SonicHKS wrote:THC, maybe you can answer this since you seem to think you know everything.

:lol:
My Sonic seems to barely engine-brake, if at all. Does that mean it doesn't have DFCO and its actually supplying fuel on decel at higher RPMs?

Textbook case of rev hang. How long have you waited for engine braking to begin?

Could also be a feature to prevent loss of traction from engine braking. VW reportedly had something like that, although my rev hang did not match up with the description of that feature.

Side note:
DFCO is not as simple as people like to think. There's a million variables used as excuses not to DFCO.
Shadow wrote:Forgot to say--if you have access to a basic scan tool, you can check the injector pulse and see what it does while you're decelerating. That's probably the quickest and easiest way to know for sure if a car has DFCO.

Which "basic" scan tools can provide injector pulse width? It's not part of generic OBDII data, so it either has to be guessed from other variables (as the ScanGauge II does) or measured by a tool that has access to manufacturer-specific data.

SonicHKS wrote:I have a BT OBDII scanner that works with my droid, but I don't really trust it. It doesn't seem to interpret boost/vacuum or throttle % correctly so I've just used it as a rough guide.

What makes you think it's inaccurate? Keeping in mind that TPS is not going to match, or even be vaguely related to, accelerator pedal position...



I had it up around 4500-5000RPM in 2nd and it wouldn't come down much, I engine-braked for a good 5-10 seconds to see what it would do. It might engine brake since it does lose a little speed but I just thought that might be from other sources of friction. My Fiero drops speed immediately when you let off the throttle at higher RPMs in any of the lower gears.

I almost seems like they removed DFCO on the Sonic so it'll coast in any gear like a slush :lol: .

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Re: Having problems going from engine brake to accelerate

Postby bk7794 » Sun Sep 02, 2012 12:14 am

I wonder if that is because of the type of mounts it has, that's why its smoother then others. I noticed this one guy broke his motor mount in his 01 civic and it was filled with oil.

I was thinking it was the fuel probably cutting since there is like no draw on the engine other then the alternator. I think I am going to do some diagnostics tomorrow with my front mount. I might do that relatively soon.
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