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Base running airflow table

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Hello! I was scanning through some of the previous forum topics looking for answers for a few questions I have. Found one that seemed to relate to one of my problems in particular. A person was having problems with their idle hanging. Andre had replied stating that the base running airflow table is generally responsible for this. Ie: if values are too high the idle will hang, and if the values are too low the engine will stall. Now I have both problems it seems, while transitioning from in gear to neutral, let's say, my engine idles up and stays there for, I'd say, about 5-6 seconds sometimes longer then slowly returns to normal idle. And while I'm in gear, usually stopped, the engine will hesitate and sometimes, not all the time though, stall out. So it sounds to me like I need to make some changes.

Andre had mentioned in this forum discussion about making a histogram to resolve this. (MAF vs ECT) with the same break points as the base running airflow table. Any ideas how to set this up? Is it a math channel or just a custom setup? As well I'd assume my MAF needs to be correctly scaled before attempting this correct? One more question, do I have to zero out adaptive idle parameters before trying to log this?

Thanks guys!! This forum is the best! Definitely one of the most powerful tools this site has to offer.

What is the engine, transmission, and the vehicle? What mods are done to it?

2001 LR4 (4.8) gen 3 LS. Mild cam 112/112/110 lsa. 550 lift both intake and exhaust. Headers, intake, that's about it for stuff that would affect airflow

Trans is a 99 Tahoe 2wd. All stock

Vehicle is a 1987 S-10

Are you tuning with HP Tuners? What mapping is in there now, and where did it come from (stock map, some previous tune etc)

Yessir I'm tuning with hp tuners, and it's got a stock tune on it from a 5.3.

*Bump*

Hi James, setting up this histogram is pretty straight forward. The parameter you want to log into the histogram is mass airflow and you want to copy the break points from the base running airflow table. Note that you'll have a base running airflow table for P/N and another one for D so you need to populate both. This is a case of starting the car from cold and allowing it to come up to temp while scanning the whole time. Once you've got the histogram filled out you can simply copy and paste into your base running airflow table. You won;'t hit every cell so you need to manually extrapolate the areas you can't reach. Do the same when the engine is completely cool with the car in gear. Naturally this needs to be done once the MAF is accurately dialled in though.

I've found that it can help to actually slightly raise the base running airflow numbers from what you actually generated in the histogram to prevent the idle dipping.

Alright so I'm trying to get my maf dialed in and the areas in gear 3125hz and above, its coming along. and I've noticed in your webinar for maf scaling that your particular engine you were getting numbers down into the 2700hz range, in park I am at about 3125hz and in gear I cant get that low period. The engine goes to about 450rpm and sounds like it's going to die. Is there something else I need to be doing? My timing is going to 3 or 4 degrees and sometimes even negative, is this something that I need to correct before I continue with my maf? I need to figure this out so it doesn't keep trying to die on me while stopped. 2001 gen 3 LS 4.8 with a cam, 112/112 duration 110 LSA and .550 lift both intake and exhaust. I dont feel like the numbers I'm getting from my afr err maf histogram when it's doing the dying thing are very accurate..

Hi all, little update on this, I just found my special functions tab in my VCM Scanner. While in gear I noticed if I played with the timing in the scanner I could get it to idle in drive without hesitation. So could this be a timing related thing? I've made no changes to my timing tables in the tune just messed a bit with it in the scanner. So would it be scale MAF in steady state and wot, then VE table then spark last to be able to get it to idle correctly in drive? And as well does anyone have injector info for 25317628? I'm getting all kinds of numbers from people online, Injector RX says 22.0lbs and I've heard 24.5 and 25.5. Tha is for any help!

The cam increases overlap which adds residual gases. That slows combustion. Advancing timing is one way to counter that, or adding air (opens throttle more).

That is mostly separate from MAF scaling.

Okay that makes sense, so when I put it into drive and start using the scanner timing controls I do that until I see the highest map reading right? And as well, my fueling goes lean when in the higher advance so I need to add to my VE table to accommodate for this? And as well, with the timing do I use the scanner to find the best timing then just put it in the main spark table? And I have noticed that if I keep my foot on the gas it will stay alive.

Or would I do it as, add 2° of timing to in drive table, reflash, etc. Until it idles then get my maf scaled in that area? Idle while in gear is the only area of my calibration I haven't been able to hit yet on my scaling or perhaps should I drill a bigger hole in my throttle body? This was something recommended by my camshaft manufacturer do to the cam and my elevation 6,000ft above sea level

You're on the right track, but you have to go with whatever the engine responds to. So let me ask you this: if you just add 2 or 4 degrees to your baseline idle tables, does it stabilize the idle? You gotta do one thing at a time. The MAF calibration doesn't have to be perfect starting out.

I added 2° to my in drive table and high octane table, with no difference idle quality in drive besides my AFR going more lean. Do I need to add 2° in my low octane table as well?

There's only so many knobs you have here. You add air (by moving the throttle with base airflow table), you add spark to advance the combustion and stabilize the burn, you run a richer AFR because that is more stable on cammed engines. If you do too many things at once you will get all mixed up and not know which thing did what.

So in your case: is the timing actually advancing from what you did? I don't know off the top of my head the names of every table to change for your exact HP Tuners configuration, as I don't have it in front of me. But basically the idea is to advance the timing (whatever tables you need to adjust that affect idle spark) 2 or 4 degrees and stabilize. You need to keep careful records of all the different things you are trying or you are going to get way lost. Keep an Excel file or some other method to record what you changed and what the result was.

Yessir understood! I have been keeping careful records of what I've been changing and I've only been doing one thing at a time. This thing had me so confused. So I went back to the basics because when I put it into gear it was surging to 1000+ then dying almost then surging. A quick check and I found a vacuum leak. So now that, that is fixed I reconfigured my tune back to the way it was for the mass airflow scaling from the webinar. And I'll be giving it another go. Thank you so much for your awesome advice. I'll be keeping you updated on my progress. I really like how you put it in your last post "theres only so many knobs you can turn" that's what made me go back to the basics and check for a leak and sure enough that was part of my problem. Check in with you in a bit

*update* so before any changes were made to the base running airflow table, I had to hold the throttle open at 4% to keep it idling. I kept moving the base running airflow table up for in gear until it was maxed out. At this point I have to hold the throttle open at 2.4% to keep it idling. And adding timing did not help. Only made it worse. So it sounds like my TB hole may need to be opened up to allow more air in when it is closed? As well when I made the timing changes, it was doing the same thing it was before where the timing dips negative. I just took off my throttle body, and I noticed that the IAC is stiff, like really stiff, does not want to move, is this normal? I'm asking because in my experience, the IAC should be able to move freely if everything is off correct? Could this be my culprit if it is supposed to move freely and not?

*update* took the iac out and cleaned it. Put it back in and under the special functions tab in the VCM scanner. I was able to control the rpm under the iac tab by moving it up and down. So I dont think it's the iac. Just must not be getting enough air in through the plate.

Oh crap I forgot you still have a cable throttle. I was thinking this was electronic throttle. Isn't there an air adjusting screw on the throttlebody, either the stop position for the throttle plate or a bypass air hole?

I do not believe there is a throttle stop screw, I'll have to check, and by bypass air hole you mean the factory hole for the air to bleed through when the throttle is shut? Found the throttle stop screw and raised it up a bit to no avail.

If so, is there a specific way to know how much to widen said hole? I believe it is 3mm from the factory.

From a few image searches it looks like those throttlebodies don't have an air adjusting screw. On a lot of cable throttlebodies, instead of a fixed hole like you have, there is a hole with a screw in it somewhere in the system (on the throttlebody itself or cast somewhere else into the manifold/air induction system). That screw is pre-set from the factory, and there is a service procedure to adjust it in some circumstances.

I think you are going to have to go back to highschool math on this one. I mean I wouldn't increase the area of the hole more than 10-20% at a time. So you'll have to use the old pie R squared formula (calculator below). Since you are in the USA most of your drill bits are in oddball standard sizes, so I'd first see what bit fits into the current one and then go up to the next one in increments of say 16th or 32nds of an inch. And find a spare throttlebody on ebay in case something goes wrong. If you overshoot you can't go down in size without replacing the throttlebody.

https://www.mathsisfun.com/geometry/circle-area.html

The whole point is you want the idle air control valve to have enough bandwith to add or take out air to control the idle as engine conditions change. You don't want to add too much air (from enlarging the hole) or the idle valve is now no longer so useful at controlling idle. You should be able to achieve your basic warm idle with no accessories when the idle valve is at about a 50% position. It really illustrates how annoying cable throttles were back in the day (they've been out of production for over 10 years now). People have such rose tinted glasses when they think about them.

Guess what?!?!?! I got it!!!!!!! It idles in drive now and all the other gears with absolutely no hesitation! I couldn't be happier. And my airflow numbers are at the stock settings, so the IAC should have plenty of wiggle room to adjust as necessary. Thank you so so much!!! I feel like I can finally move on. So next would be maf scaling and VE tuning right? And I've noticed that I've got what sounds like a back fire at part throttle, now when I make changes to my VE table, will it automatically make changes to spark? Or should I use Andre's method of modifying the stock spark advance histogram and get the spark right first so it doesn't do that? Thanks again oh so much! It's so nice to be able to just have a foot on the brake and shift into gear without it dying

What size hole did you drill? I would proceed with MAF scaling next before you tackle anything else.

Andre, feel free to chime in.

I went 2mm bigger than the factory hole, so not quite double. Ended up working really well. And roger roger! I'll be working on my maf scaling before making any other changes and waiting on a reply from Andre when he isnt busy.