Dan K
09-04-2003, 12:10 AM
Just thought I'd share a quick once over that has always worked for me...
First thing you have to do is set up all the injector constant correctly for your car. There was a good post here a couple of weeks ago that should help you set up all or your constants if you're unsure what they all are.
First thing you need to do is find an idle rpm that you're comfortable with in and out of gear. Stock idle rpm's are for stock cams. You are probably going to have to experiment a little to get an idle rpm that you're happy with. Anywhere from 800-1000rpm should cover most of the hydraulic rollers that are common upgrades in the LT1. I've found hotcam like 800-850, 230/236 like 900ish, and the 236/242 like 950-1000rpm. These should get you started in the right direction.
Next try and get your IAC counts in the 10-40 range. This should allow the IAC to adjust enough at idle and should get rid of the "tip in stumble" that some people experience with larger injectors. A good place to shoot for is 30-40 counts in gear at idle and as long as the IAC counts are greater than 0 in park you're good.
The last 2 things that you should play with are closed TPS spark advance and the maf tables to adjust your idle fueling.
Use the maf table to adjust your idle blm's and try and get them around 128. They don't need to be exactly 128, just somewhere around there. If you're idling at 11 g/s and your blm's are 140/143 then you need to tell the maf tables that the car is seeing more air so that it will add more fuel and bring your blm's down. So what you would do is go into the maf table and in the area where it shows 11 g/s, scale the values in that cell and the neighboring cells anywhere from 1-5% depending on how far off your idle blm's are. This should lower your blm's a little. Keep adjusting the maf table a little until you get your idle blm's to an acceptable area.
Now look at what your spark advance is at idle on a datalogger. Stock should be right around 20*. Look in a stock file at the closed TPS spark advance table and you'll see that at 400 and 800 it is 20*. So this is where the PCM gets its idle spark.
What I like to do is use the 400, 800, and 1200 rpm cells and fill them with the same values. Remember that larger cams will need more idle spark than a stock cam. To figure out what kind of idle spark your car wants pay attention to idle map, or put a vacuum gauge on the car. You want to use the closed TPS table to try and get your idle map as low as you can, or your idle vacuum as high as you can. I've used values anywhere from 24*-34* depending on the cam, compression, and cubic inches.
Remember, this is what I've found to work on the cars I've done. If anyone has any other ways to do any of this or if you have any comments about how I do it...feel free to fire away. :)
First thing you have to do is set up all the injector constant correctly for your car. There was a good post here a couple of weeks ago that should help you set up all or your constants if you're unsure what they all are.
First thing you need to do is find an idle rpm that you're comfortable with in and out of gear. Stock idle rpm's are for stock cams. You are probably going to have to experiment a little to get an idle rpm that you're happy with. Anywhere from 800-1000rpm should cover most of the hydraulic rollers that are common upgrades in the LT1. I've found hotcam like 800-850, 230/236 like 900ish, and the 236/242 like 950-1000rpm. These should get you started in the right direction.
Next try and get your IAC counts in the 10-40 range. This should allow the IAC to adjust enough at idle and should get rid of the "tip in stumble" that some people experience with larger injectors. A good place to shoot for is 30-40 counts in gear at idle and as long as the IAC counts are greater than 0 in park you're good.
The last 2 things that you should play with are closed TPS spark advance and the maf tables to adjust your idle fueling.
Use the maf table to adjust your idle blm's and try and get them around 128. They don't need to be exactly 128, just somewhere around there. If you're idling at 11 g/s and your blm's are 140/143 then you need to tell the maf tables that the car is seeing more air so that it will add more fuel and bring your blm's down. So what you would do is go into the maf table and in the area where it shows 11 g/s, scale the values in that cell and the neighboring cells anywhere from 1-5% depending on how far off your idle blm's are. This should lower your blm's a little. Keep adjusting the maf table a little until you get your idle blm's to an acceptable area.
Now look at what your spark advance is at idle on a datalogger. Stock should be right around 20*. Look in a stock file at the closed TPS spark advance table and you'll see that at 400 and 800 it is 20*. So this is where the PCM gets its idle spark.
What I like to do is use the 400, 800, and 1200 rpm cells and fill them with the same values. Remember that larger cams will need more idle spark than a stock cam. To figure out what kind of idle spark your car wants pay attention to idle map, or put a vacuum gauge on the car. You want to use the closed TPS table to try and get your idle map as low as you can, or your idle vacuum as high as you can. I've used values anywhere from 24*-34* depending on the cam, compression, and cubic inches.
Remember, this is what I've found to work on the cars I've done. If anyone has any other ways to do any of this or if you have any comments about how I do it...feel free to fire away. :)