Z-BOSS

I think I maybe reading this title wrong or understanding it wrong...
does a postive % change add or take away fuel

I maybe reading this wrong...

TRAXION

Positive = addition (more fuel)
Negative = subtraction (less fuel)

Tim

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TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

Kevin91Z

iTrader: (1)

While we're on this subject, I see no place to add or subtract fuel at WOT, like there is for the spark advance. Am I not seeing it? I see a Power Enrich Spark Advance vs RPM, but I see no Power Enrich Fuel Adder vs RPM. All I see is the PE Change to Air/Fuel ratio. My A/F is already 12.5:1 and I dont want to change it, so how would I add or subtract fuel at WOT? I just went to the extended VE table and changed the values at 100 KPA for my dyno runs.


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West Coast GM Shootout 2001!
1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.23 @ 107.62 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-

Grim Reaper

The problem Kevin is that 100 KPA is not PE (WOT). What happens when you are at a higher elevations and your MAP cannot register 100 KPA at WOT?

The rational for using %Fuel @ RPM in PE Mode is to ensure that things like elevation which may cause you to have significantly less MAP (80 kpa at the summit passes here is common), that you will get the fuel added.

If you only set 100 KPA, then at 80 KPA you may be too lean. And it is possible on climbing some grades tha you could hit over 80 kpa yet not be in PE mode. The proper solution is to have good MAP VE tables @ 14.7, then add %Fuel vs RPM in PE Mode.

Doing it your method, you only get fuel added at 100 kpa, anything less than 100 does not and runs lean.

[This message has been edited by Glenn91L98GTA (edited April 24, 2001).]

Kevin91Z

iTrader: (1)

I'm still not getting it. How does changing the WOT air/fuel ratio affect the fuel? I'm already at 12.5:1 like I said, and that is a good number. If I change it to add fuel wont that affect that number and cause it to run richer? I've already dialed in the WOT settings for 100 KPa, I wouldnt know how to change it back and adjust the Air/Fuel ratio without another dyno tuning session to figure it out.

There is a local track at 2900' but I rarely go to it, maybe once a year. And I certainly wouldnt hit WOT anywhere else but the track.

TRAXION

KEV: How does changing the WOT air/fuel ratio affect the fuel?
TIM: What do you mean kev?

KEV: If I change it to add fuel wont that affect that number and cause it to run richer?
TIM: It depends. This is why I wrote that P730 post on tuning part throttle fuel. Tuning your part throttle fuel curve is the most important tuning. The lower and upper VE curves are incredibly important. The WOT PE %Change to AFR vs. RPM **ASSUMES** that your VE curves are on the money. Thus, if you dial in your WOT first and then proceed to dial in your part throttle curves you will be screwed. I made a big point in that P730 post about tuning the part throttle curves first. Tuning these curves first is of utmost importance.

Now - let me explain further. WOT is engaged via a signal that indicates WOT should be engaged. This signal is based on a delta TPS at a particular RPM. In TunerCat this is called "TPS Threshhold for Power Enrichment". There is a table for normal coolant temps and a table for high coolant temps. Whenever the change in TPS readings equals the amount of change specified in this table at that RPM then the car goes into PE mode (WOT). Most often (not always!!!!) WOT is close to a 100kPa reading. Thus, you should be able to modify any point in the VE tables except for the 100kPa values and you will not affect your WOT AFR. However, as Glenn so rightfully pointed out - at higher elevations WOT will not be at 100kPa. So - as a "QUICK FIX" I would suggest no changing any VE values above 70kPa (this means the 80, 90, and 100kPa values). THIS IS A QUICK FIX. It is not the real fix. The real fix is to retune your VE curves according to what I posted in the P730 article and then go back to the dyno. This quick fix specified above will hurt you if you find yourself driving up a steep hill and NOT in PE mode. You will probably run lean and start to detonate

Tim

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TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

Grim Reaper

Actually, you don't even have to be that high (elevation wise) to not attain 100 kpa. You loose a couple KPAs @ WOT if you were to compare you baro reading with the engine off (102 kpa @ sea leve, but only 100 kpa @ WOT).

At about 500-700 feet you may be lucky to register 95 kpa, now you will no longer use the 100 kpa table but a mix of 90 and 100. A little lower, and you are just using 90.

The effects of just a little elevation is amazing on your max kpa @ WOT.

Yelofvr

I have been looking at this table and trying to make sense of it. One area I don't understand is why at 2000 rpm do the values go negative?????? I looked at the camaro, corvette, and an ADS chip for 1990 SD systems and they all go negative in this region. Does anyone understand why it works this way??? It doesnt seem to follow the VE curve. Dont understand why you want it to go leaner ONLY at 2000 rpm and richer above and below that point.

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Dave Zelinka

Kevin91Z

iTrader: (1)

Tim, first question, I meant I'm not good with percentages. So I should put my 100kpa values back to stock and use the PE %Change to modify the values? I just took another look at it and it looks like I can figure it out, but I still feel stupid for doing it my way. What about the PE %Change vs Coolant Temp? Which value does it look at first? Does it do a percentage of one value then percentage that value again for the other table?

Right now I am just "cheating" and letting the computer handle the part throttle stuff. I'm not maxing out either BLM or INT, but since I'm not at 128/128 that means I'm not running at the best efficiency either.

TRAXION

It depends. Are you willing to go back to the dyno to retune your WOT curve? How did you tune your WOT curve ... using the 100kPa region or using the PE WOT vs. RPM?

I posted HOW the ECM calculates AFR based on these tables in a previous post. It looks at both values at one time. The AFR is calculated like this ...

WOT AFR = 6553.6/((Coolant Modifier + RPM Modifier + 128) * 445)/256)

Tim

------------------
TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

Kevin91Z

iTrader: (1)

I used the 100kpa method, like I said above.

I must have missed that formula, I dont read every post.

I dont know if I would go back and dyno-tune again, unless I make a change.