Guys, I have noticed that my car feels noticeably stronger with more fuel in the gas tank than without. I am a full bolt ons m6 and upon starting off with a full tank of gas my car is very easy to get going. When the tank begins to go below half tank it is harder to start off (bogs just going from a stand still) and does not pull as hard wot, also seems to ping with less gas then with more gas. With more gas in the tank it does not bog at all and pulls like a raped ape. I am very confused . I have autotaped and autotaped to see if my car is going into the low octane table for some abnormal reason which would explane my car feeling stronger after adding gas. Is it possible that the autotap values are simply wrong for timing (my real time temps always read around 200 but when I log I get values around 190) I have ls1 edit and the timing values I get in autotap always seem to align them selves with the values of the high octane spark table. I am thinking about getting a fuel pressure gauge to monitor a possible drop in fuel pressure with more gas in the tank. What else do I need for the fuel pressure gauge to work(sending unit?). Is it possible that my in tank pump is being starved by the lower amount of fuel. Any comments are appreciated.

P.S. I have not changed the fuel filter and my car has 31000+ miles on it. Do you think this may have an effect (wouldn't think so because it only occurs at lower fuel levels).

 

I think its all in your mind, If you are anything like me you run your tank til its just about empty, for those last few miles you drive it easy, then once you have a full tank of gas you dont have to worry about running out, so you get on it and just floor it!!

 

its my understanding that when you fill the tank all the way up, it resets the timing map to the high octane one (if its not already there)

this would give you more power.

if your car then gets detonation, and consitent detonation, the computer will bump you down to the low octane timing table and it will feel less powerful.

autometer sells a really nice 180* sweep electric fuel pressure gauges for around $180 with everything you need (exept rail fitting) to measure and watch your pressure from inside the car.

 

Damn.I learned something new today.Keep it coming MightyMouse.

 

It has something to do with the extra weight and the cars ability to transfer the weight during launch. You can 'feel' more torque being used with a full tank, but if you run back to back tests at the track, the lighter will be faster (assuming traction is not a problem).

 

Mightymouse has it right. Everytime you fill the tank (you really don't have to fill it...just put a few gallons in it I think) the computer resets the timing curve to the most aggressive one. As you drive you sometimes experience KR and the computer learns to pull timing during the situations in which it occurs. This learning is wiped clean when the tank is filled.

Now, get rid rid of %100 (and I mean %100) of your KR in ALL situations (this means some pretty extensive Autotapping) and you won't notice a difference after fueling.

 

Oh yeah, moving to Computer Diagnostics and Tuning... <img border="0" alt="[Burnout]" title="" src="graemlins/burnout.gif" />

 

Is there an easy way to change the low octane values to the same as the high octane values in ls1 edit without having to type in each value manually. I am convinced that my knock sensor does not work very well at all. I get false knock <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> in 4th gear upon giving it lots of gas around 2000+ rpms but hear no pinging. When I here pinging I get no knock showing up.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by DailyAluminumBlock:
<strong>Is there an easy way to change the low octane values to the same as the high octane values in ls1 edit without having to type in each value manually. I am convinced that my knock sensor does not work very well at all. I get false knock <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> in 4th gear upon giving it lots of gas around 2000+ rpms but hear no pinging. When I here pinging I get no knock showing up.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Thats not false knock <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

your just putting the motor under a lot of load.

 

"Mightymouse has it right. Everytime you fill the tank (you really don't have to fill it...just put a few gallons in it I think) the computer resets the timing curve to the most aggressive one. As you drive you sometimes experience KR and the computer learns to pull timing during the situations in which it occurs. This learning is wiped clean when the tank is filled."

This is the most common reason. I believe it's 5 gallons.

 

Due to the lack of quality from one brand of gas to another and type of smog gas, there has to be a way the PCM can adjust for a bad tank of gas.

If the PCM sees knock that has long decay rates, then the PCM sets a bad gas bit and switches to lower octane timing table.
If will stay that way UNTIL the PCM sees at least a 20% gas tank volume increase from last time key was turned off and the next key on.

It then clears the bad gas bit and goes back to high octane timing table.
If you use lousy gas or get lots of small knocks but several knocks in a row then the cycle starts over again.

If the gas tank is less then 1/4 filled PCM will ignore bad gas bit if it had not been set before reaching that level.

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Colonel:
<strong>Mightymouse has it right. Everytime you fill the tank (you really don't have to fill it...just put a few gallons in it I think) the computer resets the timing curve to the most aggressive one. As you drive you sometimes experience KR and the computer learns to pull timing during the situations in which it occurs. This learning is wiped clean when the tank is filled.

Now, get rid rid of %100 (and I mean %100) of your KR in ALL situations (this means some pretty extensive Autotapping) and you won't notice a difference after fueling.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">

 

It's a nice feature gm put into their cars, cause all obd-II vehicles have to "know" how much fuel in tank for evaportive emissions control. Other mfg. have simular set-ups.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by DailyAluminumBlock:
<strong>Is there an easy way to change the low octane values to the same as the high octane values in ls1 edit without having to type in each value manually.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Sadly, no. The topic of importing tables from flat files (similar to exporting tables to files) has come up a few times but interest has been low. In the mean time type it in, export BOTH hi and lo tables to file and diff them to check that you haven't fat fingered.

 

Thanks guys, I just replaced my low table values with my high table values and it went away. I also zerod my maf table and adjusted my injector flow and wow, all the timing I was missing came back. <img border="0" alt="[Fluffy]" title="" src="graemlins/fluffy.gif" />