S2KI Honda S2000 Forums

Someone else expressed concern about running lean with TP/E on the "S2000 Modifications and Parts" section so I got a bit worried. In any case, I think I answered my own question. I wasn't able to find the answer on this forum, so I'll repost it for other fellow newbs, but this was taken off the Integra forum.

http://www.team-integra.net/forum/display_...ng+Common+Topic

SOME BASIC ECU INFO THAT YOU SHOULD KNOW:[B]

The ECU has 2 modes of operation:

1. closed loop
2. open loop

closed loop uses the front O2 sensor before the cat (on both OBD1 and OBD2 called the PRIMARY O2 sensor ) to control the injector opening time (called duty cycle).

In closed loop, there's 2 adjustment modes:

1. short term trim
2. long term averaging trim

your primary O2 sensor is a NARROWBAND type of sensor (see the dyno tuning section of the articles and look under Air Fuel Ratio Tuning BASICS to see the relevance of this).

Because the primary O2 sensor is too slow to react to the rapid changes in the exhaust's O2 content as the rpms rise, we need to use open loop control, once the throttle is pressed past 1/2 or when you go past 4000-4500 rpm usually.

In open loop, the ECU's programs control the injector opening time instead of the primary O2 sensor. These programs are laid out in the form of a table (see the ECU Basics article for an example of what a fuel table looks like) .

The commands for the injector are called "fuel values". The table has manifold absolute pressure (or MAP, a measure of air flow) as the indicator of how hard your engine is working . rpm is used as the other indicator. Another way of saying "how hard the engine is working" is "engine load".

The programmers enter the actual time the injector should be open for each manifold pressure (MAP) and rpm combination.

So once you press the throttle past 1/2 or go past 4500 rpm, you change from closed loop ECU control to open loop ECU control.

--------------------------------------

The stock ECU program usually runs fine in "closed loop" operation (not too rich or too lean), as long as the O2 sensor and it's connectors and the longterm trim averaging are fine .

However, the stock ECU program has 2 problems:

1. it runs too rich in open loop

and

2. the ignition timing tables are retarded too much in the lower rpms for both closed and open loop (you usually need more advance in the lower rpms and this is why your engine feels like it's lagging or bogging).

The common false idea is that you run leaner because your engine breathes better after adding i/h/e (+/- IM) and the fuel delivery stays the same as before.

The fuel doesn't stay constant though.

The reality is, in closed loop, the longterm averaging responds and changes with the extra air flow to keep the air fuel ratio near the optimum range based on the primary O2 sensor readings and so you should not run too rich or too lean.

The other reality is that the stock ECU's fuel tables for open loop operation kick you into running too rich (not too lean). The stock ECU programs for fuel delivery usually over compensates for the new mods in open loop after i/h/e is added.

Resetting the ECU doesn't change the open loop commands. It only resets the baseline primary sensor voltage after the engine has warmed up for closed loop operation and clears any CEL warning codes.

So when you have added i/h/e or i/h/c/e, the ECU isn't a nonresponsive unchanging program.

In closed loop, it reads the amount of O2 that is coming out of your header and based on this amount, it changes the injector opening using short term correction and then averages these over time for longterm averaging correction.

In open loop, the program is set. With more air flow, the ECU goes to a different MAP-rpm-injector opening combination command to deliver a set amount of fuel.

eg. using hypothetical numbers to show you the idea:

let's say at 6000 rpm in bone stock trim, your closed loop has a MAP of 2 psi and an injector opening of 55% duty cycle.

With the intake and header scavenging, your MAP (air flow) becomes higher to say 3 psi.

In open loop, the ECU reads a new MAP of 3 and reads down the fuel table commands and looks up MAP = 3, rpm = 6000, and then chooses the injector opening command for these 2 inputs. Usually, the injector opening time or duty cycle is longer or larger with a higher MAP...say 65%.

So the ECU in open loop adds a set amount of fuel to compensate for the extra air flow as the rpms rise. Sometimes the fuel value command entered in the table for a given MAP-rpm load is too much or too little. This is why you reprogram/tune and enter a better fuel value depending on what air fuel ratio you get in open loop.

SO PLEASE LOSE THIS IDEA THAT YOU RUN LEAN WITH i/h/c/e (+/- IM).

btw this is also why you need to fuel tune, even with only i/h/c/e.

DO I EVEN NEED TO FUEL TUNE OR REPROGRAM MY ECU WITH JUST I/H/C/E ? :

Another urban myth that's out there that we see every time a person slaps on an intake and then joins ti.net. is this :

i/h/c/e doesn't need fuel tuning.

Well, if you would have actually fuel tuned your engine to the new package, it runs more efficiently than stock, since the stock commands errs on the side of safer (safer = running too rich since you don't detonate).
So yes you run too rich after i/h/e using a stock program and so you should reprogram or fuel tune to get better responsiveness and more power.