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I wonder......
Does anyone know what the "fuel trim reset" function do in the scan gauge "controls" menu?

I think it's the equivalent to disconnecting the battery for a while. It resets the fuel trims to the factory default of very rich. Over time the PCM learns and adjusts the fuel trims closer to 0 based on other inputs.

2000Silverbullet wrote:I think it's the equivalent to disconnecting the battery for a while. It resets the fuel trims to the factory default of very rich. Over time the PCM learns and adjusts the fuel trims closer to 0 based on other inputs.

Perhaps this is my last resort after I put the header exhaust on. (scheduled to arrive tomorrow!!)

Reset the fuel tables after the header install anyways. The pcm relearns the fueling much faster after a hard reset compared to just leaving it alone.

Basically after each mod you should follow the example of AGrazela. Reset trims and retune. Each tuning will get your fuel trims closer to zero. The factory settings are merely a starting point to a much better tune for your car in the geographic area where you drive the car.

Today was much better.
Low humidity, IAT = 87 degrees.

At WOT:
- LTFT - 9.3
- 02(b1) - 945 {b2 deleted}
- Rail pressure - 13.9

Probably got to WOT about ten times on the way to work and tripped my KR annunciator lights (set to 2.0) only 3 times {versus yesterday when it was hot and humid I was hitting everytime}.

tripped my KR annunciator lights (set to 2.0)

What is that?

In the scan gauge, you can set the "Annunciator" to flash the bright LEDs above or below certain parameters.

Most will use this for shift points, however, I'm using mine so that IF KR goes above 2.0, the bright red LEDs come on letting me know I'm pushing too hard. I find it very helpful.

Oh, a function of the scan gauge I didn't know it would do that for KR. I use my annunciator to flash upper rpm limit.

I also use the lights for KR.

2000Silverbullet wrote:Oh, a function of the scan gauge I didn't know it would do that for KR. I use my annunciator to flash upper rpm limit.

What is gained by doing this with rev limiters and fuel cutoffs in place?

99ssei wrote:- Rail pressure - 13.9

What are the units for rail pressure?

- LTFT - 9.3
- 02(b1) - 945

Your KR is more than likely lean A/F issue. If I'm reading this right, your WOT locked in LTFT in +9.3%. Meaning your car is running lean and it's adding fuel to compensate at WOT. Your car could use some additional tuning.

The other causes might be:

* Torque reduction for the downshift when you go WOT (pulls timing manifested as KR)
* Torque convertor is still in lockup when you got WOT (with the torque convertor is still locked up, it puts higher load on the engine.)


In regards to resetting your fuel trims, like mentioned, it's important to reset them whenever you add/remove a mod. I also like to reset them between the seasons. When you reset them, it essentially resets the LTFTs to zero until the PCM can calculate the new average of the Short Term Fuel Trims (STFTs).

Lastly, what is "Rail pressure - 13.9". What is that measured in? I was expecting PSI.

TommyGloves wrote:what is "Rail pressure - 13.9". What is that measured in? I was expecting PSI.

I have no clue.

TommyGloves wrote:The other causes might be:

* Torque reduction for the downshift when you go WOT (pulls timing manifested as KR)

This sounds about right.

TommyGloves wrote:* Torque convertor is still in lockup when you got WOT (with the torque convertor is still locked up, it puts higher load on the engine.)

Is there a way to measure or scan? There is a parameter called "Engine Load" in the scangauge.

What is gained by doing this with rev limiters and fuel cutoffs in place?

Absolutely nothing.

It is the only annunciating light on my Aeroforce gauge that I can set.

What are you using for the KR light annunciator?

You might have an old version. I have v2.5 and I can use about 15 different parameters and then tell it to "annunciate" if it goes above or below a certain threshold. It's in the Annunciator set up menu. I chose to use the "Knock Retard 1" parameter (3 available). The next screen set the threshold - I chose 2.0. The next screens asks "above" or "below" I chose above.

I must have an older version of the gauge.

Those are nice features. Good to see continuous improvement.

That "rail pressure" was at WOT?
What is it at idle, light cruise?
Has it been checked with a guage on the rail?

Did you use a mechanical pressure gauge or the scangauge for the rail pressure? If you used the scangauge the readings mean nothing since that parameter is only available on diesel engines.

O2 - 945mV is within the normal range for a factory tune. Unfortunately the narrow band sensor is crazy so it doesn't say much about your fueling.

LTFT - +9.3 means you're running pretty lean. These motors typically run on the rich side from the factory so something is definitely wrong. Double check your WOT fuel pressure with a mechanical gauge.

superchargedSSEi wrote:Did you use a mechanical pressure gauge or the scangauge for the rail pressure? If you used the scangauge the readings mean nothing since that parameter is only available on diesel engines.

Scangauge. I don't have a mechanical gauge. I'll have to ask around if someone has one that can test it for me.

Headers arrived, but was signature required. Will be picking them up from UPS hub tomorrow and stopping by shop to see if they can throw it in for me. If KR persists, I'll reset fuel trim setting through the scan gauge and then take it from there.

There is no fuel pressure sensor/sendor on any GM 3800 engine/platform. You need a mechanical gauge.