Questions about Limp Home Mode

[DavidBraley]

I've been reading about the Netres chip and how it's a vital part of the limp home mode system. My present understanding of the Netres chip is it's a unique network of resistances based on engine size and cylinder count, and with the input of the TPS, MAP and other sensors, it can create an emergency fuel map that will allow the engine to continue to run under a control system that has failed in some way. I've also read it's important to choose a memcal that's the same cylinder count and as close to the cubic inch size of engine you are using. It makes sense.

Some of you know this, but I'll repeat for clarity. The engine I'm collecting parts for is a BBC that will be bored and stroked to 489 cubic inches. This engine will conservatively produce 550 hp and something around 550 foot pounds of torque (That's carbureted. Hopefully more with EFI). These numbers are approximately double the original output for this engine. The PCM I've chosen is the 7427, and I've modified it for use in MPFI mode. I'm also building my own port injected intake for the project. The transmission will be a 4L80e.

It's been a comfort to read about others having success using the 7427 for heavily modified engines. What I'm not understanding is how limp home mode will deal with an engine that needs a different fuel map at the same TPS position and MAP output from the original engine, even at low power needs.

I've read a couple of threads where others have mapped out the resistance network of the Netres chip for different engines. Is anyone out there fiddling with these Netres chips in a way that would allow someone to modify the resistance network to create a different emergency fuel map when the PCM defaults to limp home mode? The idea being if someone is experimenting with a kind of "universal" Netres circuit. A board of some kind that would allow you to create your own unique resistor network. I hope that made sense.

My last question is if the limp home mode is transmission type dependent. Can a memcal from a 7.4L truck that used a manual transmission be used in a truck that uses a 4L80e?

Again, thanks so much for your thoughts on my questions.

David