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Old 02-26-2010, 03:26 PM   #1
robertway

 
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Power Enrichment at WOT... does it ever have a chance to even happen?

***Tuning Noob Alert***

Just trying to work through the tuning learning curve so I was working through the numbers in the PE vs RPM table and it seems that GM has these cars set to command about 11.5-11.7 at WOT once enrichment kicks in, the key being once enrichment actually kicks in. Looking at the default PE Delay RPM of 5000 and the Enrichment Rate of 0.0200, does it EVER actually kick in. Seems to me it only kicks in once you get past 5000 and does it ever have enough time between 5000 and 6000 to ever get to the commanded AFR because of the 0.02 rate?

I did my first HPTuners scanning earlier this week just to start "observing" things to see how the car behaves from the factory. I noticed during one of my 2nd gear WOT runs there was a good amount of knock and a bunch of timing pulled. I do not have my Wideband operational yet so I cannot speak to my actual AFR just yet. My IATs were between 46-48F during the run so things are not too hot (I'm in Jersey so it is cold out). Being the noob I am I just want to figure out why the car is behaving the way it is from the factory before I start getting involved with tuning it myself. The only thing I can think is that because the WOT enrichment doesn't kick in until you pass 5000 rpm and the rate being so slow that during the WOT run the car is running in the low 14s to high 13s for AFR until the PE starts to kick in over 5000.

So a few questions, once you go to WOT, what AFR does the PCM target until PE kicks in? Is it 14.67?

Do the LTFT's get added to the fueling both before PE kicks in and fter it kicks in?

Correct me if I am wrong in how I am reading into what I see in the scan log below, thanks in advance....

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Old 02-26-2010, 06:37 PM   #2
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The PE can be delayed when under 5,000RPM, but it still kicks in. When the STFT's stop switching and the 02's stop switching you know you are in PE.

There is a PE enrich table that determines the AFR during PE.
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Old 02-26-2010, 06:51 PM   #3
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...and yes, the LTFT will get added to the PE.
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Old 02-26-2010, 07:38 PM   #4
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Yes, 14.67 while in closed loop.You should be able to log for open loop status (when it goes into PE mode) and the Commanded AFR PID to see and how fast it changes from 14.67. My L99 timer is factory set to 0.00 sec , meaning no delay before 5000 RPM. You can make it in come in faster by changing the ramp-in rate from .02 to .1 or .2, etc.

LTFT's only work in CL but they can cause it to add fuel at WOT if they are more than 0.0 when you go into PE mode. That's why you want slightly negative LTFT #'s.
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Old 02-26-2010, 07:55 PM   #5
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According the the Tuning School Book on the late model cars you should set the enrichment rate to 1.0 -1.2 for NA cars....
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Old 02-26-2010, 09:59 PM   #6
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So whether you are at partial throttle or WOT, once you enter PE it will target the commanded AFR based on the EQ Ratio vs RPM table until you fall below the thresholds that put you in PE mode in the first place?
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Old 02-27-2010, 12:47 AM   #7
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Quote:
Originally Posted by robertway View Post
So whether you are at partial throttle or WOT, once you enter PE it will target the commanded AFR based on the EQ Ratio vs RPM table until you fall below the thresholds that put you in PE mode in the first place?

Yes, that should start ramp-in or ramp-out based on TP.
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Old 02-27-2010, 07:10 AM   #8
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OK, tolerate me as I walk through these scenarios and let me know if my assumptions are correct;

1. I am crusing along in 6th with MAP over the default 15kPa PE threshold but TPS at 18%, I give it a little more throttle to maintain speed on a slight uphill and TPS only goes to 28%. Here I would not go into PE Mode and would operate in Closed Loop.

2. I am crusing along with MAP over the default 15kPa PE threshold but TPS at 18%, I want to pass a car quickly, drop it down into 5th and give it a lot of throttle putting TPS at 50% (over the 30% TPS PE threshold default). The car would go into PE mode and start to works towars the AFR in the PE EQ Ratio table at a PE Rate of 0.02 (the LS3 default), it does all this while in closed loop.

3. I am cruising along above 15kPa and about 18% TPS and decide to drop it into 3rd and go to WOT. The car immediatley goes into PE Mode and Open Loop and works towards the Commanded AFR from the PE EQ Ration table.

4. Finally, trying to figure out the Delay RPM, I am in first gear on a slight downhill and for whatever idiotic reason I slowly work into the accelerator, never get the TPS past 29% but my rpms go above 5000 (the default PE Delay RPM), the car will go into PE Mode I am assuming to help protect the engine and do so in Closed Loop.

Thanks in advance for confirming or denying what is going on in any of these scenarios, it will really help me understand how the car is fueling under different conditions.
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Old 02-27-2010, 02:56 PM   #9
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In theory, yes to 1,2 and 3. However, it seems that the 30% TP threshold in the table does not reflect actual TP but throttle area %. I remember reading somewhere that 30% (table) really is about 60% logged TP. When logging you can see what your actual TP% is when it goes into PE and reduce the table to get it where you want it to enter at whatever RPM. Table example - 30% to 1500 RPM, declining to 10% at 5000 RPM might be close to start and log the changes and see how you like it.

4. If the timer is 0.0 (stock L99) there is no 5000 RPM delay limit, but some trucks have a 5 or 6 sec delay. My 05 Silverado HD had a 60 second PE delay stock for some reason. Any lag going into PE when TP threshold is met is from fuel ramp in (stock = .02), .1 would be 5 times faster, or PE Mode Timer Counter settings (stock .05 x 20 per sec) = 1 second. .1 = 1/2 sec, etc. Hope this helps.
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Old 02-28-2010, 09:22 AM   #10
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Log ETC, not pedal position.

Positive fuel trims get added to your WOT fueling, negative trims do not. This is why it's good practice to get trims everywhere into the negative side.

Set the enrichment rate to 1. Anything higher doesn't do anything.

Also, you should add commanded Air/Fuel ratio to your scan. I believe it's PID.6001 in the scanner if you want to use it for making an AFR error PID.

If order to enter PE, you have to meet the TPS and MAP thresholds. Simply surpassing a certain RPM won't automatically put you in PE.

Here's what my scanner typically looks like:

Last edited by DSteck; 02-28-2010 at 09:42 AM.
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Old 02-28-2010, 10:46 AM   #11
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If the two main thresholds are TPS and MAP, with the default MAP threshold being 15kPa it seems as though the one that really matters is the TPS since it is so easy to get over 15kPa. Do TPS and ETC correlate closely? I know TPS only ever goes to 83ish% so would that correlate with ETC being at 100%?
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Old 02-28-2010, 02:14 PM   #12
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Quote:
Originally Posted by robertway View Post
If the two main thresholds are TPS and MAP, with the default MAP threshold being 15kPa it seems as though the one that really matters is the TPS since it is so easy to get over 15kPa. Do TPS and ETC correlate closely? I know TPS only ever goes to 83ish% so would that correlate with ETC being at 100%?
You're right, the throttle position is the major deciding factor for power enrichment. The pedal position and ETC are not a direct relationship. There's a long dead area in the pedal so that you have a wider drivability range. Just because you push the pedal halfway doesn't mean the throttle is open 50%. But yes, the 80-something % shown for pedal position is wide open throttle (ETC of 100%).
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