Could someone explain the MAF and spark tables?

[BJM]

I have been looking at the GNTTYPE spreadsheet for a while.

The WOT spark tables cover the ranges 400, 800, 1200, 1600, and 2000 RPM for LV8 up to 176. Are the regular tables used for the speeds above 2000 RPM?

There are 6 MAF tables shown with something called PP2counts as indices as well as a scalar. I thought there would be a MAF table for every BLM cell.

 

[bruce]

Originally posted by BJM
I have been looking at the GNTTYPE spreadsheet for a while.

The WOT spark tables cover the ranges 400, 800, 1200, 1600, and 2000 RPM for LV8 up to 176. Are the regular tables used for the speeds above 2000 RPM?

There are 6 MAF tables shown with something called PP2counts as indices as well as a scalar. I thought there would be a MAF table for every BLM cell.

The WOT spark table is for spooling, and to keep the car out of detonation. Thou on the TTA they have the enable set to 99.6%.
Personally, I just always set it at 99.6.

yes, at over ~2K you change to the main timing table.

The way I use/understand the MAF tables and scalers, is:

Just to pick some numbers and give some meaning to things.

Say table 3 has a scaler of 20, and the 10th entry in that table is 200. To convert that to gm/sec., you multiply 20x200, and divide by 255. So you'd have 20x200, and that's 4,000 divide that by 255 and you have 15.6. So at that table value, ie MAF frequency the ecm thinks the engine is using 15.6 gm/sec of air.

Now as you tune the car if at 15 grams /sec as indicated by the scanner if your lean, you would want to find that 15 in your tables, and then slightly increase the entry value to have the ecm think it's actually using more air at that frequency. And you'll note as you edit things, they begin to shift, and it can get kinda confusing to get it.

The thing with having the MAF tables correct, is so that as you go into PE mode, and the ecm calulates the new AFR, it's basing that calulation on the MAF tables. So yes, you want them as close as can get em. A WB is REALLY helpful for doing them.

When I'm roughing out the MAF tables on a hot rod, I set the PE TPS enables higher then stock so as to get as much of the MAF tables as correct as I can. But, I'm extremely careful about not building much if any boost when doing that, and then immediately set them back down. Headgaskets won't last long at 14.7 AFR in boost.


You'd do well to just forget about what cell your in. Look at the gm/sec to see what the ecm needs.

But, in part tuning is an art form so you'll probably see other ideas about what works for others.

 

[BJM]

bruce

Thanks for the fast response. I understand the timing now.

Almost there for the MAF tables except for a couple of things. I have a really low idle BLM cell. What table do I edit to bring the value up. What is the index into the table (what units). What is each of the 6 tables for?

 

[bruce]

Re: bruce

Originally posted by BJM
Thanks for the fast response. I understand the timing now.

Almost there for the MAF tables except for a couple of things. I have a really low idle BLM cell. What table do I edit to bring the value up. What is the index into the table (what units). What is each of the 6 tables for?

Forget the cell.
Need to get your scan tool out and see where you are Gm/Sec and then get into table one and correct it.
If it's reading say 5 gm/sec, then figure out a value of say 5.2 gm/sec and see how you are.

No units, it's just the math the ecm uses to make the calculation.

They use 6 tables, cause of the limit of how many columns the processor can handle. That and limits of the MAF's frequency range. You can only divide things up so much. After a given point you have to round things off, and then all the extra division is lost anyway, if you were to try and expand things.

 

[dennisL]

BGM, you mentioned you have a really low "idle blm cell". First, this can be caused by more than just the maf table needing a tweak. Make sure the injector constant is correct for your injectors, then shave a little off the battery offset table ($4C1) values because you've probably increased the fuel pressure. Nobody uses 35 - 38 lbs pressure any more, do they?

Using the stock chip blm boundary #'s, the first two cells are used for idle (engine warmed up). It drops down to the next row above 9 gm/sec. As Bruce said, this puts you in maf table #1. I'm gonna guess that you're only using the last 4 entries in this table, so these are the numbers to tweak. If the blm # is too low, then reduce the maf table number. You don't have a lot to play with in that first table. By that I mean, changing a value by 1 or 2 will affect the blm. (The other tables are not so "sensitive".)

Don't forget, a bunch of things can affect idle fuel including the IAC.

 

[bruce]

Originally posted by dennisL

Don't forget, a bunch of things can affect idle fuel including the IAC.

IAC being miss-set can cause an off idle stumble, and idle speed problems, but AFR?.
What am I missing?

 

[BJM]

I have never actually programmed a chip at all, just trying to understand it first.

I know my idle cell is low because my valve cover is connected to the turbo inlet so I have no "leaked" air. I was trying to understand how that might be altered in the tables.

I currently drive with a Jay Carter chip where the higher flow cells are at 140-144 and the idle is at 105-110 which seems odd to me. I have 30 lb injectors. It was the same with my stockers only a bit higher. The middle cells are scattered in between these values. Would it just be a matter of fiddling with the 6 MAF tables?

Also, where is the equivalent to pump shot enrichment found?

 

[dennisL]

BJM, if you want to fix the low blm at idle, change these two locations in the chip:
$4CA: change 23 to 1E
$4CB: change 1D to 18

This will bring the blm up but you won't see it at a steady 128 unless you tweak maf table #1.

The "pump shot" for us is acceleration enrichment or AE. There's not enough room here to explain it, but next week I'll be sending a detailed description to Eric Stage 1 for his web site.

In short, there are 2 kinds of AE, one controlled by change in throttle position, and the other by change in LV8. Look for tables that are labeled "TPS AE" as they control the pump shot. The LV8 AE stuff is disabled.

 

[BJM]

dennisl

What exactly is the injector offset doing? It looks like its making a huge correction based on system voltage. Are your changes intended to increase pulse widths at idle due to the fuel pump pressure dropping at idle?

 

[dennisL]

If you make the changes I recommend, you will be reducing the injector pw at idle. You said the blm was low, which is rich so you need to reduce the inj pw.

I looked at a JC chip for stock injectors and the injector constant ($436) is reduced 1, which is good in your case. I'm just guessing you have the same chip. Look at $436 and see if it is 47. Stock is 48.

The inj offset is added to the calculated inj pw as the last step before it is sent to the injector drivers. The original #s where intended to compensate for variations in alternator voltage, but they add just a little too much to the pw. I figured your blm at idle was about 20% low so I suggested a 20% reduction to the offset.

The offset is not related to fuel pump pressure but, since you mentioned it, what pressure are you using?