This is a learning exercise and I'm looking for some pointers for various reasons.

When u change your IC to accomodate larger injectors, name every table u change and why...........

Just looking for some fresh post ideas and hopefully iron out some wrinkles.

later
Jeremy

 

Some of the changes are dependent upon which injectors are being swapped in, from what is being swapped out. In some cases I'll change the short PW compensation table. I'll do this before any VE table changes to bring the BLM back in line. Usually doesn't take much of a change.

AE tables: AE is mostly PW based, so a larger injector will provide more AE. Some masks will have the AE compensated for against the current PW. In this case the AE will not need to be changed as much.

Cranking fuel: if the crank fuel is PW based I'll change the base cranking PW by the ratio of injector flow change.

Proportional gains: most are PW based and need to be changed by the ratio of new to old injector flow. This is to prevent excess prop gain and the surging it creates.

Sometimes I'll change the async PW values such as the minimum async PW, and the sync-to-async and back thresholds.

Can also tweak the double-fire to single-fire thresholds.

Then of course the VE table. All I do is some VE LEarns to bring stuff back into line. This is required as the linearity of injectors varies across makes, models, and fuel pressure.

RBob.

 

RBob,

The short PW compensation table you are talking about, do you know if this is present in $0D? What exactly does that function do?

 

Friend of mine just put 24's on his '91 305 TPI. So I'm going through this right now. So far, I've scaled the VE tables down by the ratio of 19/24. That got very close to 128.

I'm working the AE tables at the moment. He indicated there was some stumbling during throttle transitions (likely too rich like Rbob said above) so I leaned out the AE vs delta TPS to start by about 15% (kind of an arbitrary starting point as I didn't want to go the full 19/24 right off the bat). Have yet to hear feedback. But if it improves, I may try a little leaner to see if it gets even better.

He actually just bought a 350 to complete his original intention of going to the 24's, so this tuning excercise is simply an intermediate place holder to keep the car running ok until he does the swap. In any case, it's a good learning experience for me. Not to mention a chance to utilize what I've learned here on another car besides my own, and possibly encourage another hot rodder to jump into the wonderful world of tuning.


Though, I am in fact curious what this short PW table is...

 

Yes it does. The table is at $496F with a bias at $4967. The bias is subtracted out with the table value being added. So can reduce the PW if desired.

The table is based on PW, which needs to be less then 3.8 msec. The looked up value is added to the current injector PW. The bias is then subtracted off.

Note that this mask will run a TBI or a CPI setup. Not sure if the small PW comp table is used on both or just one or the other. Placing large values in the table would show if it is being used. Go slow, take notes.

RBob.

 

In the $0D mask, table $496F is selected for use by a flag at $400E, bit 4. In the TBI calibrations, this flag is unchecked and only the bias is used for short Async PW compensation. For the CPI/PFI calibrations, the bit is checked and the bias value is zeroed out resulting in only the table bieng used for short Async PW compensation. HTH

 

Exactly what does the injector flow rate constant do for all this? I realize other things will need to be adjusted but what does this one constant do and what in the code is calling for it or correcting. I did a search and see it calculates the base pulse constant. I think I found my answer here. I was just looking for the base fuel calculation.

PW = BPC * MAP * ~T * ~AFR * VE * BVcor * BLM

BPC being the engine displacment to fuel injector flow ratio
MAP is manifold pressure
~T is the inverse coolant term (from CTS & IAT)
~AFR is the inverse air fuel ratio
VE is volumetric efficiency from the calibration
BVcorr is the battery voltage correction
BLM is the block learn

I was looking for this.

New flow rating = [square root of (new pressure /old pressure)] x old flow rating

Re-writing above formula to find new pressure:
[New flow rating / old flow rating] = square root of (new pressure /old pressure)

Square both sides of equation
[New flow rating / old flow rating]^2 = new pressure /old pressure

Multiplying both sides of equation by old pressure
New pressure = old pressure * [New flow rating / Old flow rating]^2

 

I messed up and should have said $8d code specifically

 

For 8D and the IC code. See this https://www.thirdgen.org/techbb2/sho...hreadid=276420

$8D doesn't use a BPC like the TBI bins do. $58 does IIRC.
Basically the BPC does the cyl size and IC math and makes it a constant so the code doesn't have to do all that math.

For the short PW table-

Say your setup calcs a PW of about .9 ms.
This is below the minimum physical time needed for some injectors to work.
So there is some code that uses that table to add a little bit of time to the calc'd PW to compensate for the time needed to open and close the injector.
Also injector linearity will vary from brand to brand and size I would imagine.
The table is used to compensate for that too.
Bruce was the person to ask on this stuff.......

 

Curious.... did you change the injector constant? I have LT1 24's on a LO3 topped off with TPI and I got BLM's near 128 +/- with no changes to the VE table. So far I've only adjusted the spark table, injector constant and scaled the AE by 19/24. I know I have to add fuel in the lower RPM's, but that is due to the headers and 3" exhaust.