TBI to MPFI netres modification

[87tpi7749]

Hi everyone, I'm new here so you can kick me if you want. I've spend days searching all the good forums trying to find the information needed to properly run a 16197427 TBI ecm in PFI mode. I did an Edelbrock MPFI swap and it runs horrible @idle and 1700rpm. The only info I could find on the netres mod at TGO and fullsizechevy was that Ken at HP Tuners knows how to do it. There was a post by Ken at fullsizechevy in June of 2004 and he was going to post here about the mod, but I searched and can't find it. Please help. Or flame me if you wish.

[Casey]

First you have to modify the Memcal. Install the jumper as shown in the picture.
If you can't solder, find somebody who can.



Second you need to modify a few of the AE sync to async and BPW values and set the fuel mode to
PFI.


Switches:
1 CPI or PFI 1=PFI

Constants:
Sync to Async BPW<= 1.296998 Msec
Async to Sync ( Or PFI Double Fire) 1.495362 Msec
AE Min Aysnc or TBI Min Aysnc PW 1.90735 Msec
AE Max Aysnc or TBI Max Aysnc PW 6.10352 Msec
Low BPW Offset vs BPW Table Bias .0305176 Usec
Min Period Double Fire 0 Usec
Deg Delay From DRP to Inj Fire 0 Degrees
Sync Min BPW 1.296998 Msec
Sync Default BPW 1.693727 Msec
Cylinder Volume 1.0266 L/Cyl
Injector Flow For TBI 6.335433 Gms/Sec *OR* Injector Flow for PFI 12.67087 Grams
Async to Sync if Map > (TBI Only) 104.4 kPa
Async to Sync if RPM > (TBI Only) 6375 RPM
Sync to Aysnc if MAP > 104.1 Kpa
Sync to Async if RPM > 6350 RPM


I have attached a Zip file with a high res pic of the memcal mod, working 7.4L calibration and text printout of the cal.
We don't support OBDI, but there is plenty of free and shareware stuff out there. Don't forget you will need an Eeprom burner and eraser..

http://www.hptuners.com/pub/PFI Memcal Mod.zip



Enjoy,
Ken

[gsjmtnman]

Are these settings the essential changes for MPFI conversion, or are they specific for a 7.4L motor? Thanks

[gsjmtnman]

anyone?

[dimented24x7]

There are three firing modes in the PCM: TBI/batch/bank fire. The memcal mod is needed to tell the injector drivers when to fire. The injector drivers for MPFI are software driven using the timer output compare lines. There is a hardware timer/flag in the MCU with its rate set by the memcal configuration that is used to trigger one of the two injector drivers at the appropriate interval.

In addition to this and whats stated above, you will also need to change the crank fueling as its in terms of pulsewidth rather than g/cyl fuel. Some have complained about over/under fueling during cranking causing hard starts due to the change in injector flowrate and firing stratagy.

Lastly, you will also need to jumper the current sense resistors with 16 gauge or larger wire so the injector driver will not enter peak and hold mode. There is a lot of info on thirdgen.org about the 93-95 truck PCMs. I (and others) have done a lot of work with these PCMs, so there is pretty much everything you could possibly want to know posted on the TBI and DIY-Prom forums.