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.

 

Did anyone ever tell you that you're the man??? I'm learning quite a lot just reading your posts.

 

One other thing, if you have a large cam...

Changing the BLM boundaries can help keep the idle on it's own cell without fluttering between adjacent cells.

Like, upping the lower MAP to 35 or 40, and the lower RPM to 900 or 1000.

That would probably help too.

 

Very good point. Setting up your blm boundaries is key to tuning also.
If anyone else has more to add feel free. If you've got a different/better way post it.

 

Great post DAN!

I am nearly ready to start tuning my car soon, i just need a ECM piggyback adapter thingy. I've got Tunercat.

Bo you by any chance have a tune file for a 230/236 cam, ported Lt1 heads for a 93? I would like to start somewhere, and maybe your experience can get me in the right track.

Just asking.

Do not let this post die.

 

You fail to address one thing...

Overlap... With raw fuel going though the exhaust it will create a false lean to the O2 and make the car use more fuel at idle...

Anyway around this??? more spark advance???

 

I just got my new clutch in, So now I will begin tuning the car. I started off with a mail tune from madwolf. And his tune was really helpfull, made the car run alot better. But the low rpm's are still a little off. What would be a good setting for my Closed TPS spark advance for my cars mods. Or how would I go about picking the right one for me, right now I have 26*@400 27@800 and 30*@1200.

 

I have a file to start with that I could send you. I was doing a car with the 230/236 and Lloyd Elliott heads but the owner of the car found a couple of mechanical things with the car that he's fixing before we finish. I could send it to you and help you through the tuning if you wish.


OK...explain this to me and maybe I can figure it out. If you have raw fuel going through the exhaust how does it create a lean condition at the O2?
Just off the top of my head you could switch to an open loop idle and tell the ECM how much fuel to use at idle. I think this has been discussed here before, but quite a while ago.

Monk -
I would suggest you set the timing in 400, 800, and 1200 to the same amount. I think it's easier to see the effects on timing in regards to map if you do. What you have should be pretty close really. Just play around with it a little bit and see what timing works best.

 

O2 sensors do not see O2, they see CO2... If there is raw fuel there is C6H6 and O2... Since there is no combustion there is no CO2. It will think its lean because the mv will go low and will add fuel, that is why I always smell fuel at idle...


How do you make the car go into open loop or fix the blm for the cell 16? I read another post, but all it said was make the car go into pe mode when in idle but that didn't work...

Let me know

 

If the pe idle trick didn't work, then I don't know what to tell you.
No experience with your problem.

I wonder if someone has found a way to lock cell 16 in the same manner that you can lock cell 15?

 

O2 sensors don't read CO2, they read O2 (oxygen).

Rob
95Z28

 

correct, right on,

when they see to much o2 they richen the mixture up. hence the name

 

What do you mean by addjusting the blm up?

 

Yeap I read, my bad... It measures the differential O2 in the exhaust vs the ambient.. It breathes through the cable

I think the trick with the blm is that you adjust the idle part extreemely lean and it will hit 160 and although the stftms will keep adjusting, it takes a while and by then you are moving again... or lower the blm constant and it will be faster...

 

Dan,

What program are you using for tuning?? You mention maf tables (plural) I have LT1edit and it only has one maf table. What are the other tables used for?

-Tony