Help braking by putting transmision in neutral

[majicmeow]

Cool... ever do anything with an F-Con Vpro? I've never played with emanage, microtechs or haltechs so I can't speak for them. I've spent some time on the 2JZ's in particular with the Vpro... totally insane system :p , but not enough to consider myself "great" at tuning them

Tuning the new cars is pretty hard unfortunately. I've helped on a Supercharged Elise project that used the Vpro as a "standalone" but the engine wouldn't run without the lotus ECM. Since we couldn't tune the Lotus box, we had to basically give it the inputs but cut its outputs (except VVT) and let the Vpro run the rest. Was a blast to tune!

The same has to be done for any "modern" system as the new ECM's are locked down pretty tight and are immune to the old EEPROM swap or rewriting of the unit due to signature checks across modules. With the SC Elise as an example, other modules in the car "looked" for the ECM's signature check so even if we got the Vpro to work the VVT, the car wouldn't behave properly. Unfortunately, the electrical side of the new BMW twin turbo engines or even the relatively basic Toyota 6cyls are so ridiculously complicated, even a system as powerful as a Vpro or AEM cannot handle all the necessary outputs or data throughput (yet )

I do agree with you regarding the turbo cars and detonation. However, sudden lean is an issue for any engine but is exemplified when under boost. This issue can be solved while still retaining the ability to shut down the injectors, but requires a fine tune with hardware fast enough to make the determination of fuel cutoff against cylinder pressure.

Glad to see a guy who actually gets into the nitty gritty and enjoys looking at ignition maps.

-Aaron

[ISLAMATRON]

nope never dealt with the Vpro, just waiting for a customer who will let me tune 1 for the first time, dont know anyone running them around here too much either.

All those things you mentioned about the newer models is why most people dont tune them too much around here.

That supercharged Elise project wouldnt have been in Ann Arbor was it, I used to step into their facility up there while in college. They were allways trying crazy things with lotus' up there.

[majicmeow]

The Elise project was in Calgary, all the way up here in Canada. The Vpro kind of rules the woods around here, so to speak... anyone with a crazy tuned Japanese car with a standalone usually runs the Vpro out in this area.

The Elise was just a one off project for a very happy customer 911TT's couldn't keep it out of the mirrors during track days

Sorry for dragging this OT...

[safeaschuck]

Could you potentially have a switch that when you would brake, the transmission goes into neutral so the engine wouldn't go against the brakes thus saving fuel, helping the brakes and save the engine

So what it comes down to Shrek, in plain english, is the engine is actually helping the brakes as long as your not pressing the throttle, and turning off the fuel when slowing saves more fuel than idling the engine in neutral. (sorry if you got that already man!)

As for engine wear if the (auto) trans was in neutral and the engine dropped from say 3k rpm to idle as you braked, but you needed to get going again suddenly, the engine has to come back up to speed to meet your demand (causing wear and also using fuel) and the trans might get a jolt (and some wear) trying to feed the power in in a hurry. So it's probably better just staying engaged.

The idea i got this from is that since you could press the accelerator when braking(heel and toe thing in other forms of motorsports)that it would mean that some of your braking would go to slow the engine turning the wheels instead of using all of it to stop.

When you push the accelerator under braking and it pushes against the brakes that is plain old left foot braking, it can be used to increase grip on FWD cars when cornering OR shift the balance of a RWD, 4WD & FWD car to get it to turn tighter, looser or slide.

Heel and toe is where your engine is disengaged (clutch pedal pushed down) so no pushing against the brakes, it's only used on fully manual trans cars (i.e. 3 pedals) and helps you get the stick shift in to gear quickly when your braking without having to ram it in or grind it. The whole point of heel and toe is to make use of the engine to help slow you down, so kind of opposite to left foot braking.

[Belatti]

A Scarbs explanation of heel and toe:

http://scarbsf1.com/heel_toe.html

Driving arround the Andes like I have done many times and you´ll need engine braking unless you have some racing ventilated discs, calipers and pads installed in a real light car

About injectors being shut down or not, I still see no links, I might be blind or something

Just is case, a link I have found, nothig "official" from a manufacturer:

http://www.gassavers.org/archive/index. ... t-865.html
http://www.dailyfueleconomytip.com/driv ... e-braking/

[Roland Ehnström]

Please provide your reasoning as to why engine braking gives higher gas milage

I have no real proof other than the fact that eco-driving schools (at least here in Sweden) actually teach you to use as much engine braking as possible (when you would otherwise have to use the brakes, that is; of course any retardation should be avoided if at all possible). majicmeow has explained what is also my understanding of the reasoning behind this, but I do not have enough technical knowledge to prove it myself.

[lz2lps]

Not sure if this will be helpful, but here is one graph logged from my 1994 Honda Civic:



TPS (Throttle Position Sensor) - green
RPM - black

The other two are AFR (Air Fuel Ratio measured with wide band O2) and Injector Duration - can't name the colors

The ECU is the factory Honda ECU, but chipped. Data logging protocol was also added to the new EEPROM.

The test performed is to lift off the throttle at around 4700 RPM - engine braking.

As you can see from the injector duration graph (the lowest one), the ECU shuts off the injectors, until the RPM reaches 1085.

I was told that with modified engines this fuel cut is not implemented to improve cooling.

Also the consumption of a 4 cylinder engine when idling is probably under 1L/hour - so compared to switching to neutral, probably the fuel save is not that much, if even exists (due to the braking effect).

[majicmeow]

Bellati,

I can't provide you with any direct links to any of the BMW training literature I have. I value my job too much to give that out.

I CAN tell you from personal experience with the new generation BMW 6 cylinder engines that this DOES in fact take place. I am able to monitor injector pulse and voltages on my testers during overrun and can confirm that they are shut off or cycled at a VERY low rate during overrun.

On my Yaris, I can actually hear the injectors stop "ticking" as the engine is in overrun. I cannot verify it with scantool data, as I do not have a Toyota scan tool in my BMW shop

I cannot tell you for sure why the duty cycle would be dropped to near 0 as opposed to complete shut off, but the ECM has a mind of its own and does it for reasons I can only guess at. Cylinder temp could play a large role in the decision to run at low duty cycle or off mode, as could emissions...

lz2lps,

Are you running a Hondata EPROM in that ECM? Its been years since I've looked at Hondata, so I'm not sure where they are now in terms of capabilities...

[lz2lps]

lz2lps,

Are you running a Hondata EPROM in that ECM? Its been years since I've looked at Hondata, so I'm not sure where they are now in terms of capabilities...

No, the factory Honda ECU can easily be modified (thanks to pgmfi.org) and there is free software you can use to modify the different tables and add additional code (e.g. CROME). It has place for an external EEPROM. You just need to solder a socket and a couple of resistors and capacitors. All tracks and holes are already on the board... You can switch from the original program/tables to the external EEPROM just by placing a jumper

It also has serial port, just need to solder a header on the board and TTL to RS-232 converter (i don't have RS-232 on my laptop, so there is one more step - RS-232 to USB).

The program on the new EEPROM is the program that comes from the factory, but from an ECU for another engine, because the data logging plugin was written for it. I just played a little with the fuel tables (out of curiosity, not that much for tuning . What can you tune on a stock engine... )

Having said all that, i do not understand that much of engine tuning. Just "playing" in my free time. Honda engines and electronics proved to be idiot proof

Note that i am talking about OBDI ECU, not OBDII, which i think are not that easy to modify

Just wanted to show that this fuel cut thing is not that new, because it is in my 1994 Honda, and i think earlier models also have it too...

[ISLAMATRON]

but you said it yourself, the injectors turn off until you reach 1085(close to Idle)RPM, so you might as well have just put it in neutral(injectors would still go to 0 cycle) and braked with your foot... it would lead to less powertrane wear, and the fuel is the same.

Idle rpm should be about 800

[lz2lps]

but you said it yourself, the injectors turn off until you reach 1085(close to Idle)RPM, so you might as well have just put it in neutral(injectors would still go to 0 cycle) and braked with your foot...
Idle rpm should be about 800

I have the feeling that either i wrote it wrong or don't quite got your answer

The injectors are OFF ABOVE 1085 RPM, and the ECU switches them ON again when the RPM goes BELOW 1085. You can also see the AFR graph that it goes to its MAX value, if you doubt that somehow the ECU messes with the data . The wide band O2 in this case was directly connected with the laptop. Its value is not read via the ECU data logging protocol.

I usually do not go to such low RPM when braking in gear (this even probably will stall it), so during the whole braking the injectors are OFF. I really feel that have more control without going to neutral and it noticeably helps me while braking.

Probably it also help to not lock the brakes that easily and to have the power from the engine if something goes wrong (things happen...)- i think this is the main reason they teach it in driving schools, not the fuel economy. Not a very pleasant experience when you go with the clutch in through the corner, because you mis-shifted on corner entry and you are trying to "find" the correct gear . Also i prefer to have both of my hands on the steering wheel in this case too.

Anyway, blipping the throttle while braking and going through each gear on down shifts probably doesn't help with the fuel economy, but i really don't care . 6 l/100km highway (or 39 mpg) is not that bad (this is when I am keeping the pedal from the metal and the RPM under 3000).

I used to switch to neutral when was driving my first car - old Russian one, that had carburettor, instead of EFI, but i know that some carburettors also have fuel cut-off solenoid.

There are other ways to save fuel and probably one of them is to make lighter cars I have one favorite quote about this:

Driving involves 3 basic abilities: Accelerating, braking and turning. More power will only help acceleration. Lower weight helps all three!

Or what about the A/C? Or keeping the speed through the corners? Or watching far ahead so you do not accelerate/stop hard between traffic lights, etc...

But I am sure you already know everything that i wrote

I also agree that the brakes are for stopping the car, not the engine , but a little help is welcome too

[peteskar]

The new audi TDI 3.0 only fires the injector on post combustion to aid in engine braking and it helps to keep engine noise down. The new 3.0tdi in the Q7 is amazingly quiet and smooth.

[ISLAMATRON]

I have the feeling that either i wrote it wrong or don't quite got your answer

The injectors are OFF ABOVE 1085 RPM, and the ECU switches them ON again when the RPM goes BELOW 1085. You can also see the AFR graph that it goes to its MAX value, if you doubt that somehow the ECU messes with the data . The wide band O2 in this case was directly connected with the laptop. Its value is not read via the ECU data logging protocol.

I usually do not go to such low RPM when braking in gear (this even probably will stall it), so during the whole braking the injectors are OFF. I really feel that have more control without going to neutral and it noticeably helps me while braking.

Probably it also help to not lock the brakes that easily and to have the power from the engine if something goes wrong (things happen...)- i think this is the main reason they teach it in driving schools, not the fuel economy. Not a very pleasant experience when you go with the clutch in through the corner, because you mis-shifted on corner entry and you are trying to "find" the correct gear . Also i prefer to have both of my hands on the steering wheel in this case too.

Anyway, blipping the throttle while braking and going through each gear on down shifts probably doesn't help with the fuel economy, but i really don't care . 6 l/100km highway (or 39 mpg) is not that bad (this is when I am keeping the pedal from the metal and the RPM under 3000).

I used to switch to neutral when was driving my first car - old Russian one, that had carburettor, instead of EFI, but i know that some carburettors also have fuel cut-off solenoid.

There are other ways to save fuel and probably one of them is to make lighter cars I have one favorite quote about this:

Driving involves 3 basic abilities: Accelerating, braking and turning. More power will only help acceleration. Lower weight helps all three!

Or what about the A/C? Or keeping the speed through the corners? Or watching far ahead so you do not accelerate/stop hard between traffic lights, etc...

But I am sure you already know everything that i wrote

I also agree that the brakes are for stopping the car, not the engine , but a little help is welcome too

Well we were strickly talking about decreasg fuel consumption, although the OP may have been talking about racing. But you may have a point that if the ECU does indeed turn off the injectors above 1085 then keep it in gear above that if you wanna save fuel, but it still does put more wear & tear on the power/drivetrain. Obviously street driving and track driving require totally different driving styles.

[Belatti]

This thread should go to the Automotive category.

[Shrek]

In the beggining it was for Formula 1 but now there at automotive