[Diy_efi] 16197427 PCM in PFI Mode ?

[Kevin Jacobson]

I am hoping that someone can help me determine the proper memcal 
modification to allow me to run my 16197427 PCM in a PFI mode instead of 
the normal TBI mode this was normally used in.

I  have found information from google searches that indicated that Pin 
13 of the 16-pin resistor network needs to be "shorted" in order to set 
the PFI mode for an 8 cy application. (Fires injector drivers every 4th 
DRP).  Unfortunately the gentleman who posted this info over two years 
ago to another forum cannot be reached to ask the obvious question 
"Shorted to what?"  My present application  fires  the injectors  twice  
per crank revolution (verified on an oscilloscope) as I would expect 
from the original TBI app. When I ground what I think is Pin 13 of the 
the resistor network per the partial instructions (he didn't say to 
ground pin 13) I get  something that appears to be for a 6 Cyl 
application, not the every 4th DRP I would expect.

Any help would be appreciated.

Background on the application:  Originally,  1994 Suburban K2500 with  a 
454 and originally a TBI.  The new application is an Accel/Lingefelter 
Oval Port TPI setup on a 540 Cu/Inch torque motor.  The engine is a 
roller cammed Merlin III Block with the Merlin Cast Iron Oval Port 
heads. The combination is designed to idle, make right around 500 HP (at 
4500 RPM) with a 680 Ft/lb torque peak at 3000 RPM. The 540 is built, 
but not in the vehicle until the Accel BB TPI is a little more tuned on 
the 454. I realize the 540 and 454 will be quite a bit different in 
their fuel and timing, but I thought it wise to tune the induction to 
something close on an old engine before breaking in a new engine on a 
computer/injection system that had never been fired. I would like to 
retain the stock computer because of the 4L80E Trans and due to the 
hassels of replacing the wiring harness should I go to something else. I 
have overcome the peak and hold injector drivers forcing them into a 
saturated mode all of the time by replacing the current sense resistors 
with 0 ohm shorts. The present Accel TPI (8 30lb Injectors in two banks 
of 4) works well on the 454 and it starts right up, runs well, doesn't 
throw codes,  and is controlling the fuel delivery in closed loop and 
WOT modes just great. I have an Innovate Motorsports wide band O2 
monitor and nothing is going lean.

The only problem I am having now is on deceleration where I sometimes 
get an RPM hunting going on. I suspect this is from the very short pulse 
widths the injectors are operating at and would like to move to the PFI 
mode of the PCM I already have mostly working. I am also considering a 
piggyback 7730 which I already have, for fuel and timing control, but 
don't really see the need if I can get the 16197427 to go into PFI mode.

Any suggestions or comments?

Thanks,

kwjacob at icsaero.com