Crazy thread title, but I couldn't think of anything better.

OK, you're in 2nd gear and in traffic. Things are slowing down so your car has to go slower and slower. You are not on the gas nor have you depressed the clutch yet. As the car gets slower, suddenly there is this feeling of "release" almost like you have depressed the clutch (but you haven't yet---but of course, you have to soon ...).

What is doing that?

This has always happened even with my other cars.

Just curious to know what the clutch/transmission is doing? :smile:

 

I think it's the ECU going from engine braking (no injection) to getting ready to run at idle (squirting gas).

Just a guess though.

Matt

 

I can confirm this. Usually happens right around 1800 RPMs for me. Quite annoying.

 

yeh, it's pretty abrupt on our cars. i just clutch-in around 1800rpm
as mentioned above or half clutch it, or tap the gas slightly while
you continue to brake past the 1500rpm range...i do this when i might
need to re-accelerate in 2nd from a slow roll.

 

Mine does this as well. I have only been able to replicate it in 2nd as well, doesn't seem to happen in the others. Very odd.

 

Hmm interesting.

Yeah, sometimes I can prevent it by giving it just a little gas (and hoping the guy in front starts rolling soon!)

 

I complained about this initially a few years ago on my 11/02 build 03MCS. I drove with shop foreman in my car to show him, & we also rode in several showroom cars that did same thing. It was there with version 32 stock software, & also with version 36 & with version 39 mandatory upgrade. Has not changed with GIAC install, VGS or anything i've done. I live with it and try to compensate but it is annoying.

 

basically what I am doing is heel and toe... i am still applying my brakes while i tap the gas a little bit...it doesn't hesitate at all nor is it dangerous of hitting the car in front as you're still applying the brakes.

 

I just started posting about this problem in another thread ("I'm noticing a lag @ 3krpm")

I really can't remember if I have had this problem all along or if it just started.
what are your experiences.

 

I don't see it too much as a 'problem.' I had the same effect in my Subaru and my Toyota pickup.

If Dr. O's (second post above) explanation is correct, then it should be normal and should be in all MCSs. Although I suppose the computer could make it a smoother transition from 'no gas' to 'with gas.'

 

I have it but thought that I was crazy or all alone (no comments on that)

The ECU moving from braking to idle make most sence

 

I have felt it in all my manual transmission cars.

I take it as a perfect opportunity to do a clutchless shift into neutral :smile:

 

I have felt this in all of my manual cars as well.
I have always thought that it was the engine speed matching the speed of the driveline.(RPM"S) The RPM it ocures at would be different for each gear.
During engine braking, once the engine has reached the driveline speed, it causes that little bit of, where the engine is no longer braking, the feeling of no resistance, and will eventually lug, making the engine turn slower than the drivline speed.
It wouldnt be the ECU telling the engine to go from idle to throttle. As you let off the gas pedal a long time ago, the TPS sensor already told the ECU that the throttle plate is closed when you let off of it. If you leave the clutch engaged, the engine would eventually lug itself to a stall. Maybe the effect is intensified due to the SC?
Am I making any sense here?
Of course this is all my opinion.:smile:

 

very true

 

Under engine breaking, there is NO INJECTION AT ALL! as the rpms drop, at some point the car has to squirt gas, and this happens at an RPM above idle speed. I don't think our cars are smart enough to match revs, but I may be wrong here. My Mustang (92 EFI motor) has something similar, an electronc dashpot, that keeps the motor from dieing when you put in the clutch. When it had a carb, it just sucked massive vacuum, and would burble and bang as gas got sucked into the exhasut manifold.....

Matt

 

Hmm... I guess I don't understand this explanation.
What is the "driveline" as opposed to wheels, gears, clutch, engine, etc.? Aren't wheels, gears, clutch, engine, etc. all rotating "together" when the clutch is engaged? What is this 'driveline' that is rotating differently?
(Please educate me! :smile

 

There is injection when there is engine braking. Another reason why automatic trans get worse mileage than manuals. It takes gas for engine braking. When you disengage the driveline,clutch, you are making the brakes do the work,not the engine. So they get better mileage. Yes I understand there is also driveline loss in a torque converter,this contributes to the mileage as well.
When a trannny is spinning faster than the engine, it is called overdrive. yes thats whats going on in the autotrans when it shifts into overdrive. It is so common these days, its not really colled overdrive anymore.
The driveline consists of the tranny and the halfshafts ect. When you are coming to a stop,or a slow in this situation,eventually,the driveline, matches the engine RPM.So the engine is no longer creating braking force. If you downshifted into the next lower gear, the whole process will happen again.Which is why I stated it will happen in all gears. It is a matter of what RPM your driveline is at compared to the engine RPM.

 

OK, K4KAS, I think I know what you mean. That can't be it if I understand you correctly. The engine revs do/must match the transmission (driveline) as long as the clutch is fully engaged (i.e. not slipping). When I am slowing down and the clutch is engaged all the driveline elements are moving 'together' and there is no 'catching up' of certain parts. So, I think Dr. O's explanation makes more sense.

 

K4KAS nailed it. Explaining it is not that easy. I have noticed it in all manual vehicles I have driven. The lighter the car the more noticable it is. Especially a Formula Ford! To me it was always a sign I was in a gear higher than needed. Kenchan has the right idea with a correct heel and toe downshift you miss the whole engine/driveline lurch, or like others have said, just depress clutch a little sooner.

I'll take it over an automatic any day

 

I log RPMs via injector #1. When engine braking, RPMs (as logged via the injector) goes to 0!

Matt

 

Ah ... the cold truth of data. I love it. :smile:

 

Ok then give us your explanation of the cause of that "releasing" feeling when slowing down?
As I stated, this was only my opinion. ASE certified back in 93/94. Technology has changed a bit since then!

 

I just read the "Fuel Injection" section of my Bentley manual, and sure enough it says that the ECU reduces the fuel feed when your off the gas (of course), but provides more fuel as the revs approach idle speed. So, I'm pretty sure that's what I'm feeling. So it is not so much a "releasing" as a mini "surge" as the engine is receives more gas.

 

I always wondered what that little surge was. I just chalked it up to the quirky charms of the car and used it to shift to Neutral.

Now it makes sense.