Basic Tuning Questions
 

I have some general questions regarding my tune and am hoping I can get some clarification on what I should be looking for to ensure my tune is 'safe'.

Background:
I'm running a stock F-body TPI (MAF) on a ZZ3 crate engine in my 1985 1/2 ton 4x4 Suburban (Auto w/3.42 gears) using the 165 ECM.
My tune is basically an 89' APYU bin with some minor tweaks to the idle speed, disabled VATS and EGR and modified the injector voltage offset to match the 24# Bosch III injectors I am running.

I've run some datalogs and overall, I think they are pretty good- The truck runs well but I'm not sure what specifically to look for to ensure the tune is a 'good', daily driving tune. I don't need to squeeze every HP out of this truck- I prefer reliability and good driveability under all conditions vs peak power.

One of the questions I have is regarding BLM vs INT numbers-
I notice the BLM and INT stay within a couple of points within each other most if the time but I notice the overall counts are higher (over 130) when it's cooler out and when it's hot out (85 and above) the BLM and INT is around 128 most of the time.
I've also noticed the BLM and INT values go up during heavy acceleration- Is this expected? Do I need to do anything to compensate under this condition?

I can upload an example datalog and copy of my $6E bin if interested.
Any advice would be more appreciated.
Thank you!
Elm

Re: Basic Tuning Questions
 

Elm, tuning consists primarily on fuel control. The engine takes in a given amount of air and we tune that air with a certain amount of fuel, whether idle, part throttle or wide open throttle. When it is cooler out, the incoming air is much more dense, thus you will see a slightly leaner mixture. Despite seeing that slightly leaner condition in your BLM (higher numeric value), the ECM has O2 correction in which will maintain the correct air/fuel ratio it is being targeted for. Yes, under heavy acceleration with a load, the engine is taking in a greater amount of air, and the ECM is forced to play catch up with that air, because remember, the ECM is tuning fuel to a given amount of air that the engine is taking in. Your's may be slightly more signifcant than other's because you are running an engine that makes more horsepower (more air), so you will need to look at your acceleration enrichment tables which is designed to help the ECM maintain the proper air/fuel mixture during acceleration...

Re: Basic Tuning Questions
 

Thank you- That helps!
I was misunderstanding the BLM and INT values and thinking that >128 was rich and <128 was lean but it's actually the opposite.

Since this is a heavy truck and the engine tends to be under a constant load just to move this tank around, it probably will need some tweaking compared to a lighter F-body. I notice when logging the INT will swing from 105 to over 160 depending on if I'm coasting or under heavy acceleration but the BLM swings less wildly (which I understand being a more long-term value) and will go from a low of 117 to a high of 136 depending on temperature and load.

So when I'm shooting for the 128 numbers, should I be focusing to get that number while at a steady cruise or do these values need to hover around 128 during transitional periods of heavy acceleration/towing and/or coasting as well? I don't think my tune is really too crazy far off the mark so I don't want to over think what I should be focusing on.

Using TunerPro there is a flag that toggles between Rich/Lean so I'm curious what it's calculating or displaying to me (actual calculated A/F ratio or that the ECM is running Rich /Lean?) as when my BLM/INT go numerically higher, it stays more consistently on Rich were when I'm running closer to 128, it toggles between Rich/Lean fairly evenly.
I know the next step is to install a WBO2 to watch the actual A/F ratio but I wanted to get a better understanding of what I am looking at with the tools I currently have.

Thank you for your time!
Elm

Re: Basic Tuning Questions
 

The INT's job is to swing back and forth to drive the BLM's in the direction that it needs to go to maintain a stoichiometric value, this is referred to as short term and long term fueling in the later PCM's as well. Ideally, 128 represents the programmed stoich value, which can be changed to whatever you want it to be, so it is important to at least hover in that 128 BLM range at first when tuning, then later on you can find out what your engine likes through datalogging and testing, whether the engine likes more fuel or less, and tune it accordingly because every engine is different....

The ECM has a range in which it can correct up to, I believe the OBD I systems have a 6% O2 correction threshold, or somewhere in that area, so if you see your BLM value off by 6%, there is no reason to be alarmed, it will correct itself and maintain stoich despite your BLM numbers being a little off. Once you exceed that threshold though, that is when you go into your VE and make the necessary changes in a certain RPM range area, like say when you gently apply the throttle and BLM starts to slip away from your targeted value, you would either increase fueling, or decrease fueling depending on which way the BLM is being driven in a particular area. If BLM remains constant while gently applying your throttle then you know your tuning is good in all area's, but if it suddenly goes off when you stab the throttle, then you know you need to dial in your pump shot (acceleration enrichment) to help the ECM be ready for when it happens the next time to keep up with the sudden rush of incoming air.

Re: Basic Tuning Questions
 

Awesome- Thank you! This actually makes sense now :)
Looks like I have some more datalogging to do and tables to look at.
Elm

Re: Basic Tuning Questions
 

Just a couple more questions:
What is the difference in use of the Power Enrichment tables vs Acceleration Enrichment tables? They almost kinda seem the same but I'm I'm not sure which table is utilized when and/or if they are related? In what situations would you change one vs the other?

In looking a the MAF tables, I'm trying to understand what these are used for?
Do these tables increase/decrease fueling directly somehow or is this strictly measuring amount of air for a given RPM that is used indirectly to make other calculations?
I guess my real question is that if I am using a 350 bin with a factory stock TPI, would there really ever be a reason to look and/or modify these tables?

Sorry for the 'basic' questions but I want to make sure I truly understand the relationships of these tables before I start making changes.
Thanks!
Elm

Re: Basic Tuning Questions
 

Under AE event fuel falls out of atomization due to reduced VAC that occurs when the throttle blades opens. compensates with more fuel to maintain stoich(1.00 lambda or 14.1/1 for E10).

PE provides more fuel under load so as to produce a cooling effect to reduce detonation possibility. 12.8 may produce more power than 14.1(stoich) as well.

Re: Basic Tuning Questions
 

Thank you for the explanation!

The current challenge I have is that I'm running lean at idle for some reason but within limits pretty much everywhere else.
At idle, my BLM will hit 152 or more (but INT stays in the 128-130 range).
The BLM 'Cell' is 0.
Exactly how do I get Cell 0 a little richer? More importantly, what constitutes these 16 Cells (what table(s) make up these cells)?
Do I adjust MAF table 1 and bump the gr/sec in the area I see running lean?
Do I adjust the Scalar for MAF 1? Both or neither?

I want to ensure I'm using the proper method to get the desired result vs just trial and error changes to random tables and hope I hit a combination that works.
Any advice would be most appreciated.
Thanks!
Elm

Re: Basic Tuning Questions
 

ezobens I know you have the maf system but on a few of my tunes I had the same issue with sd most of the tables seemed fine close to 128 but the idle would be very lean didn't matter what I set the ve too

I had to play with the the o2 settings took it from 148 range to the 126 range