G'day...I've been reading about porting the Plenum chamber/runners and intake manifold. With the increased airflow and better air design, does the ECM increase the fuel flow automatically? and if so, is this done by reading the oxy sensor in the exhaust or what?

Or is the fuel curve in the ECM hard coded based on what chip you happen to be running at the time? and does it have any intelligence to increase or decrease fuel flow rates?


Cheers Wayne
New Zealand

The amount of fuel given is changed via the readings the ECM gets from the O2 sensor only when in closed loop

In open loop WOT it refers to the parameters set in the chip

Oki doki....Is open loop only achieved at WOT? or What dictates/triggers open vs closed loop?

Basically your car is in open loop when first started in the morning until the the O2 sensor warms up and is able to give readings to the ECM. This is when the computer is able to make adjustments to timing, fuel, etc to obtain the proper air/fuel ratio. At WOT it ignores the O2 readings and for the most part reads only what is programmed in the chip (such as advanced timing).

Gotcha DannyT...Some of the guys here have also been talking about the thermostat having some effect on the ECM and the need to get the car to run up to 180 Deg etc, is this true?

Sorry for all the questions mate...

Is there a book I can read re the operation and the relationships between the various mechanisims within the Camaro TPI/ECM unit etc? I'd like it to be reasonably 85 IROC specific. I wanna start to learn about the EPROM function if I can. There aren't any guys locally that do chips and I might need to do my own, though the cost of the gear to do it here in New Zealand may end up being cost prohibitive, I'd still like understand it.
I have a copy of the 85 Camaro shop manual but I don't think it goes into detail about explanation of the system itself.


Cheers and thanx for responding.

The ecm reads temperature from the front of the intake manifold, right below the thermostat. If you've got too low of a temp of thermostat, it'll allow the coolant to flow through at a lower temperature and the computer will compensate by adding extra fuel. Computer controlled cars are designed to run at a specific temperature range(typically 180-200 degrees fahrenheit), and running colder than this can increase fuel consumption and emissions.

Until the exhaust is heated up enough for the oxygen sensor to function properly, the computer will base the fuel and timing off of calculations it makes from reading the mass air flow sensor and the manifold absolute temp. sensor. After this, the oxygen sensor is included to make the air/fuel ratio more precise. Even if the oxygen sensor malfunctions, after a certain amount of time the ecm will force itself into closed loop. Once in closed loop, it can learn(to some extent) what kind of fuel and timing the car needs under certain conditions, and reference this in the future.

This is my basic understanding of some of the computers functions, and I'm terribly sorry if I am wrong about something. I'd hate to misinform you. As far as a book, I'm not sure of one. Reading the boards and checking the DIY prom board may be of benefit to you. You'll recognize the guys that you can really learn from eventually.