Jump to content
SAU Community

Fuel Cut On Deceleration?

benl1981

By benl1981,
in General Maintenance

 Share

Recommended Posts

benl1981 Grand Master

benl1981

Posted
Posted

Since fitting a PFC I notice that the injectors don't pulse on decel. Or as soon as the throttle is closed (assuming still ingear). This is to save fuel, just wondering how the ignition still carries on. The engine keeps going because of the inertia etc but I assume the spark plugs still spark but there is nothing to ignite but the engine keeps going I guess.

Cheers

Link to comment
https://www.sau.com.au/forums/topic/90436-fuel-cut-on-deceleration/
Share on other sites
siksII Grand Master

siksII

Posted
Posted

how do u know that the injectors dont pulse? i really doubt it...

im assuming u are talking about how the injector duty drops to zero(powerfc) on no throttle sometimes, it does with my car too and believe the injectors are still injecting, just too small an amount to register.

Cubes Grand Master

Cubes

Posted
Posted (edited)

The PFC and stock ECU does cut fuel on deceleration to conserve fuel.

One good reason to use lots of time decelerating, also saves your brakes. :P

You will notice in the rev/idle menu of the pfc there is 2 options that allow you to set the fuel cut return rpm. The RB20det's are typically set of 850rpm a/c off 950rpm a/c on.

Edited by Cubes
siksII Grand Master

siksII

Posted
Posted

so in theory if this is the case, there would be NO exhaust gases coming out of the exhaust when injectors are at 0%, just air?

In that case the exhaust would all of a sudden go very quiet would it not, and i dont think that happens....???

Cubes Grand Master

Cubes

Posted
Posted (edited)

lol.

Roll down a hill and turn the ignition off, be sure not to have your steering lock up.

Tell me if the exhaust still has noise. :P

On deceleration, a car that has deceleration fuel cut sounds different to a car that doesn't have it.

Edited by Cubes
benl1981 Grand Master

benl1981

Posted
  • Author
Posted

My car is quite a bit louder as soon as I lift of the throttle. The smallest throtttle brings the injectors on again and it is quieter.

Just wondering if the spark plugs still spark while on fuel cut....I didnt think it would be good as it is running lean - i.e. no fuel - but I guess there is no load..

Since I found out this if I'm coming up to a set of red lights I'll just leave it in gear and hit brake... I used to sometimes knock it into neutral, this would be using more fuel and also there is no engine braking.

siksII Grand Master

siksII

Posted
Posted (edited)
lol.

Roll down a hill and turn the ignition off, be sure not to have your steering lock up.

Tell me if the exhaust still has noise. :P

On deceleration, a car that has deceleration fuel cut sounds different to a car that doesn't have it.

i will try it next time i drive, although my exhaust is nearly silent most of the time anyway so it will be hard to tell...

i always leave it in gear until im nearly at a standstill, i dont trust the car to stay on when dropping to idle especially with the random turning off problems that people get..

edit: and how do u explain bens exhaust noise when injectors are at 0? surely just the air is not making the exhaust sound loud?

Edited by siksII
benl1981 Grand Master

benl1981

Posted
  • Author
Posted (edited)

Are you running standard cat back siks? I wouldnt mind putting a stock cat back on mine so it doest hang as low and is a bit quieter. Not that mine is really loud though.. its a kakimoto cat back.

Would I lose much putting standard cat back on? I have 3" dump/front/3"cat

The engine is under huge vacuum on decel - not sure if this contributes to the louder noise. Its more noticeable below 3500rpm. My exhaust gets quieter as you rev it :P

Edited by benl1981
siksII Grand Master

siksII

Posted
Posted (edited)

i have a full 3 inch exhaust from turbo back, and the muffler has 4 inch tip. not sure about the cat though.

mine is one of the quietest i have heard, not much noise on or off throttle it doesnt even have a proper muffler in the middle so it must be a good mufller, i think its an apexi super megaphone.

although, above around 5500 it changes tone and goes quite loud, people driving behind me say it sounds like i have an external gate at high revs :P

Edited by siksII
siksII Grand Master

siksII

Posted
Posted
Check the internal design of the muffler, some jap mufflers I've seen tend to taper down to a smaller size than the entering and exiting pipe, as a result its a quiet muffler.

It may also be quiet as it may have a center muffler.

the muffler is definetly straight through with no tapering at all..

and it does not have a center muffler, only one of those skinny hot dog things that is about half an inch thick around the pipe.

in my car the intake and engine noise is way louder than the exhaust, which is the opposite of most others ive experienced.

Cubes Grand Master

Cubes

Posted
Posted (edited)

Thats all good then.. :P

Just a well designed muffler.

I've got a rather larger (as big as will fit) aussy straight through muffler on the end of mine with a resy in the middle.

It was fairly quiet with the stock turbo on it, since I bolted up the new turbo with a slightly larger turbine housing it has got a little louder.

Should also mention mildsteel is quieter and less drony than s/steel.

Offtopic lol

Edited by Cubes
siksII Grand Master

siksII

Posted
Posted

yeah more gas going through it i guess u cant help the extra noise...

i have stock turbo and 10psi so im sure that helps with the quiet-ness :P

the cat back came with the car and im sure its at least 5 or six years old so if anything its probably louder now then when new!

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • Kapr
      ECU sees many times the speed than speedo does (R34 swap)

      By Kapr · Posted

      The car/ECU will have all the sensor that it needs and expect to have. I think i do not have to explain to you how the Link is way better specialy if you have swapped engine   I just do not want to deal with any "problems" cuz i have only Nistune which i learned is not that great and in my case cant even deal with that speed problem (Link can) And of course it will be way more easier to tune and diagnose and safe. And for the ECU/speed problem...i dont know.
    • wizlb
      Who has a Infiniti Q60, Q50 (V37)?

      By wizlb · Posted

      Per Mark Roberts of Sonictune: Mark Robert Author At this time, no. No ETA either 2016-17 models. You will be able to purchase and install a 2018.5+ TCU though   TCU purchasing and pricing info! As we near the release of TCU tuning, I am going to answer some questions I get asked often.   What do I need for TCU tuning? At this time, you will need a 2018.5+ TCU to be able to tune. If you have a 2016-to early 2018, you will need to replace your TCU with the newer version. One good way to know if your TCU is good is if you have auto upshift in manual mode in 1st gear around 6500 rpms. If your manual 1st gear goes to 7k rpm and will hit the rev limiter unless you shift, you have the older TCU.   Why do I need to buy another ecu license/phone flash if I already have it on my ECU tune? The TCU is its own computer module. It is completely separate from the ECU. Because of this, you will be required to purchase a TCU license and, if your tuner has it, the phone flash license required to tune it via phone/bluetooth.   Do I need TCU tuning? TCU tuning is NOT required. However, the faster your setup, the more it will assist in track and dragy time consistency.   If I’m ECU tuned by (tuner A) can I get my TCU tuned by (Tuner ? Yes, since it’s a different module and a completely separate flash, you can have two different tuners. However, it is highly recommend that you have both tuned by the same tuner. For me, my TCU tuning will directly complement my ECU tuning style and features and running my ECU and another TCU or vice versa MIGHT cause some issues. At this time and for the foreseeable future, I will only be tuning my current ECU tuned customers TCUs.     I have a SYVECS AWD controller. Do I still need it? Yes! The AWD controllers main job is to control your AWD system. However, with TCU tuning, you will no longer need the auto-shift function as that will be done through the TCU. The AWD controller will still be very beneficial for racers looking to maximize traction on the launch.     Shift schedule changes: holding gears longer at lower pedal input as well as max shift rpm changes. Please note, the new ECU race rom coming out will address 90% of the shitty drivability issues these cars have through custom maps from myself and Racebox—as well as others I am sure.   Increase shift speeds: as seen in the videos I’ve been posting, the TCU shifts much faster once tuned.   Increased shift pressures: as also seen in the videos, much firmer full throttle shifts.      
    • wizlb
      Who has a Infiniti Q60, Q50 (V37)?

      By wizlb · Posted

      Per Mark Roberts of Sonictune:     Mark Robert Author At this time, no. No ETA either 2016-17 models. You will be able to purchase and install a 2018.5+ TCU though   TCU purchasing and pricing info! As we near the release of TCU tuning, I am going to answer some questions I get asked often.   What do I need for TCU tuning? At this time, you will need a 2018.5+ TCU to be able to tune. If you have a 2016-to early 2018, you will need to replace your TCU with the newer version. One good way to know if your TCU is good is if you have auto upshift in manual mode in 1st gear around 6500 rpms. If your manual 1st gear goes to 7k rpm and will hit the rev limiter unless you shift, you have the older TCU.   Why do I need to buy another ecu license/phone flash if I already have it on my ECU tune? The TCU is its own computer module. It is completely separate from the ECU. Because of this, you will be required to purchase a TCU license and, if your tuner has it, the phone flash license required to tune it via phone/bluetooth.   Do I need TCU tuning? TCU tuning is NOT required. However, the faster your setup, the more it will assist in track and dragy time consistency.   If I’m ECU tuned by (tuner A) can I get my TCU tuned by (Tuner ? Yes, since it’s a different module and a completely separate flash, you can have two different tuners. However, it is highly recommend that you have both tuned by the same tuner. For me, my TCU tuning will directly complement my ECU tuning style and features and running my ECU and another TCU or vice versa MIGHT cause some issues. At this time and for the foreseeable future, I will only be tuning my current ECU tuned customers TCUs.     I have a SYVECS AWD controller. Do I still need it? Yes! The AWD controllers main job is to control your AWD system. However, with TCU tuning, you will no longer need the auto-shift function as that will be done through the TCU. The AWD controller will still be very beneficial for racers looking to maximize traction on the launch.     Shift schedule changes: holding gears longer at lower pedal input as well as max shift rpm changes. Please note, the new ECU race rom coming out will address 90% of the shitty drivability issues these cars have through custom maps from myself and Racebox—as well as others I am sure.   Increase shift speeds: as seen in the videos I’ve been posting, the TCU shifts much faster once tuned.   Increased shift pressures: as also seen in the videos, much firmer full throttle shifts.      
    • The Bogan
      NC MX5

      By The Bogan · Posted

      The fancy pants red shock tower brace is finally incoming from MX5 Mania, getting it shipped from 'Merica has been a long and problematic process, and GWR, the 'Merican supplier will not ship directly to consumers outside of the US, Mania basically had to order a heap of them, the colour choice was silver, or red, and we all know anything red adds 5 killerwasps of dynotorques..... Whilst it does fit over a 2.5, and I've seen a few photos and videos of it being installed and fitting, google also says it might get real close to the FAB9 intake front runner, people in the US says it does fit with the FAB9 intake, except for one person who said it slightly touched.......so there is that.....LOL..... As it seems that I am the first in AU to have this combination of parts there's no local knowledge about fitment, so I'm just a willing guinea pig in this endeavour, I'll cross my fingers and toes and hope for the best In other news, I ordered stuff from China  on the same day I ordered the 23° silicone bend from Victoria, the stuff from China arrived a day ago, the 23° silicone bend is still travelling around Australia thanks to Australia Post, and "may" be here next week
    • Duncan
      Who has a Infiniti Q60, Q50 (V37)?

      By Duncan · Posted

      Very good news...I contacted Racebox about it last night. My car is a 2016 so remains to be seen if it is compatible, requires a TCU swap, or is impossible.
×
×
  • Create New...