What EXACTLY is Injector Slope? - Pontiac GTO Forum
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post #1 of 3 (permalink) Old 10-07-2005, 02:09 PM Thread Starter
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What EXACTLY is Injector Slope?

I am primarily talking about what a Predator actually "does" when adjusting the slope to the minus or plus side of scale.

I have searched and read these forums for days and seen a lot of references to it, and settings used. I have googled it, yahoo'ed, and even excite'ed it and I can not find a good explaination for exactly 'what' slope is or what exactly it changes about fuel delivery.

The closest thing I can find is this article:

and this article (scroll to middle of page)

But both articles fail to explain the following:

Does adjusting slope plus or minus change:

A. the pressure the fuel is being discharged from the injector? -- or -- Does it change the amount of fuel delivered?

B. open or close the injector sooner or later?

C. richen or lean the cylinder?

D. change the spray pattern of injector? (make it flow in more of a stream or mist)

My biggest reason for concern is; I am finding in order to get no KR and -3 to 0 LTFT's, I have to go -5 to -9 on Slope and + 6 to +9 richened on Fuel. (these settings depending on whether I modify Factory or Pred. Perf. tune)

I am concerned by going rich one way...and "minus" on slope -- what I was actually 'doing' inside my cylinder and for fuel delivery. Am I drowning the cylinder, or starving it?

Hope someone can give me a simple, layman's answer to some of the above.

I am not one who's satisified with just knowing how to tell time....I want to know how the watch works
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post #2 of 3 (permalink) Old 10-07-2005, 02:39 PM
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Injector Slope
Use to determine the injector size and also to correct the long term fuel trims.

* Injector change: To properly set up injector size it is recommended that you multiply the current slope by injector % change.
#24 to #30
(30-24) / 24 * 100 = 25%
so multiply the entire slope by 25% to get you in the ballpark.
* Determining long term fuel trims: Long term fuel trims are an accumulated value of fuel added or subtracted during closed loop operation.

To verify and tune for long term fuel trims, drive the vehicle for 30 minutes or until warmed up, monitor long term fuel trims and get an average value. The easiest way to do this is to get on the highway, enable cruise control and sit at 55mph while monitoring the data. Ideal values should be in the 0 to negative 2 range.
* Once you get the average long term fuel trim value:
o Positive long term fuel trims
For a positive value you subtract that value in percent in the predator injector slope. It is also recommended to lean both fuel tables by the same percentage.
o Negative long term fuel trims
For a negative value you add that value in percent in the predator injector slope. It is also recommended to richen both fuel tables by that same percentage.

Once adjustment is done and tune installed, take the vehicle out and verify the long term fuel trims per previously described method. Adjust again if necessary.
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post #3 of 3 (permalink) Old 10-07-2005, 03:10 PM Thread Starter
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I've seen that on Diablo's website many times in the last few weeks of this searching and tuning saga. I've even read it over & over and even out loud.

And I even e-mailed them about it this week, because I think it's wrong......

Because it says.....if you're positive on LTFT you go minus on slope (which is correct) and then you LEAN the Fuel (which is NOT correct)

That is the very opposite of every RWTD tune I've seen #'s on. James RICHEN's fuel for positive LTFT's--as positive LTFT's indicates you're already lean.

What I want to know is by richening fuel and then going "minus" on slope, what effect is that having? By going minus on slope...am I leaning myself out more, and counter-acting the richening of fuel....I want to know exactly what slope actually does to the injector and it's spray pattern or fuel delivery and pressure.

Last edited by AGR81; 10-07-2005 at 06:21 PM.
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