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 Fuel Ramping

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Name : Charlie
Age : 32
Location : Toledo, OH
Joined : 2011-05-17
Post Count : 3911
Merit : 30

PostSubject: Fuel Ramping    Sun Nov 10, 2013 10:35 pm

Not sure exactly what I'm asking for here, but let me try and see.

Scott was telling me that the stock tune for our cars ramps the fueling so that it's not 100% until you throttle up.

I think?

And that it should be tuned to be 100% at all times?

Is this why I see a spike of KR when entering WOT for a second or 2 before it drops to 0? Is it fueling?

I am trying to understand why I see KR for only a second or two then it goes away after I am WOT.

I dont think it's false KR because it never happens any other time. It only happens when I smash the gas pedal then disappears after a moment or two.

Is it safe to say it's because of my tune/fueling?

Thank you! yay
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Name : Todd Balestrini
Age : 35
Location : Beaufort S.C.
Joined : 2013-07-08
Post Count : 293
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PostSubject: Re: Fuel Ramping    Sun Nov 10, 2013 11:52 pm

Are you watching timing? I know my eclipse shows knock and then the computer starts to pull timing until the knock drops. Don't know if it's the same for the Riviera. Here is a old datalogger file from my eclipse, you can see the computer trying to control knock. Of course this was at 24psi and the computer failed to control it lol. But this is a good example of seeing the knock, and then it drops as rpm's climb.
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Name : Aaron
Age : 40
Location : C-bus, Ohio
Joined : 2007-01-13
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PostSubject: Re: Fuel Ramping    Mon Nov 11, 2013 12:30 am

Could be PCM cutting timing like Todd says. It takes a second or two to react to KR. Can't know for sure because we don't know at what RPM/gear it's happening.

If it happens before a downshift, the high load at low RPM will encourage KR. Then after it shifts down, the RPMs are higher and load is less, so KR will disappear. Tuning downshifts to occur earlier (w/ less throttle %) can erase KR caused by high-load at low/RPM.

Or it could be your fuel maps (MAF table) aren't asking for the correct fueling % as you increase throttle. There are 30 or so MAFF steps as you go from idle to peak RPM. If your MAF table is off, your LTFT will be on the + side. PCM can still compensate, but imo it's slower if your tables are way off. The OEM tables are set for 3.8" pulley, so 3.4" does require a tune for optimum air/fuel.

Btw, the idea that your injectors should be "100% at all times" is misleading. Your injectors should never be on for 100% duration - this is static operation (bad). The injectors open and close for an exact period of time for each cycle. This period is called the duty cycle, and determines how much fuel enters each cylinder. The duty cycle is very exact, proportional to the amount of air measured by the MAF sensor. It changes according to what the engine is asked to do.

For idle and cruise, commanded A/F ratio is usually 14.7:1. Even so, the amount of fuel changes as the amount of intake air changes. Under heavy throttle commanded A/F goes down to 12, 11, even 10:1. At WOT fuel is delivered to match the RPM value in the MAF table. It increases as RPM (intake air) increases.

So in short, fueling is always changing based on commanded A/F ratio and mass air flow.

'98 SC Riviera 281k miles 298 HP/370 TQ 0-60: 5.79s ET: 13.97 @ 99.28 4087 lb 20.1 avg MPG Nelson Ledges Lap: 1:30
3.4" pulley AL104 plugs 180 t-stat FWI w/K&N 1.9:1 rockers OR pushrods LS6 valve springs SLP headers ZZP fuel rails
KYB GR2 struts MaxAir shocks Addco sway bars UMI bushings GM STB Enkei 18" EV5s w/ Dunlop DZ101s F-body calipers
EBC bluestuff/Hawk HP plus SS lines Brembo slotted discs DHP tuned Aeroforce Hidden Hitch

^^^ SOLD ^^^ frown

'05 GTO 85k miles 0-60: 4.8s 16.9 avg MPG Nelson Ledges Lap: 1:26
Because fun

'70 Olds Ninety-Eight Holiday Coupe 116k miles 455 Rocket V8
Because cool

'95 Celica 152k miles 0-60: yes
Because free
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Name : Evan
Age : 25
Location : Granite Falls, WA
Joined : 2012-07-13
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PostSubject: Re: Fuel Ramping    Mon Nov 11, 2013 1:06 am

Boom. Roasted
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Name : Todd Balestrini
Age : 35
Location : Beaufort S.C.
Joined : 2013-07-08
Post Count : 293
Merit : 5

PostSubject: Re: Fuel Ramping    Mon Nov 11, 2013 2:24 am

llamalor2112 wrote:
Boom. Roasted
Yea that killed the head gasket lol. Which is why im a firm believer in non metallic head gaskets, they act as a "fuse"
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Joined : 2007-07-01
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PostSubject: Re: Fuel Ramping    Mon Nov 11, 2013 2:26 am

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