There seems to be a lot of discussion on the ECU and its learning capabilities. I am new to the Z but not new to EFI. Most ECU's have built in fuel and timing maps for WOT. The computer does not consider o2 readings. The ecu reads partial throttle and idle AIR FUEL ratios (VIA a voltage) of the O2 sensor only under partial and idle loads. The the ecu has what is usually refered to as long term and short term fuel trims. Thus "learning." If you add mods that change AIR FUEL ratios I.E. intake headers and exhaust and the motor moves more air the ratio will naturally be leaner. If this mixture is to lean the enginge will potentially knock. Then the ECU will pull timing. and whala loss of hp. Unless I am mistaken and we have a wideband 4 or 5 wire O2 sensor our ecu will not make adjusments to WOT injector durations.

 

I can see why nissan did what they did in that 80% of buyers just drive to and from work in their Z and treat it like a normal car. If something is out of spec you get a SES light come on.

vs

automatically adding more fuel to make the A/F good

This is especially dangerous if the ECU won't add fuel at WOT with some mods cause not only is it lean, it's at the engine's limit

So you're saying the only time the ECU will try to add more fuel is at partial throttle? hmm interesting - stupid design, but interesting...

 

What I am saying is that during wide open throtle ECU's typically looks at either a MAP sensor or a MAF sensor and a given rpm to determine what should be the corect amount of fuel and timing. They also adjust to a change in throttle position or change in MAP or MAF for suden accleration so you do not end up with what is refered to as tip in detonation. This is usually refered to as "an acclerator pump" ECU's take readings off several engine sensors air intake temp, coolant temp, throtle position, crank position, top dead center.....etc. I have read several posts about breathing mods allowing for short term power gains and eventually the car loosing power. If the ecu is adding fuel at WOT to account for the more air how could this be hapening. Dynos with A/F ratios have confirmed that the cars are running lean. Lean conditions can lead to detonation. the knock sensor will pick up detonation and retard timming. I do not claim to know the intricacies of the Z ecu. Like I said I am new to the Z. What I do know about EFI comes from my experience as a certified AEM tuner and from playing around with hondata on my supercharged prelude.

 

that is interesting and confirms a few things i was thinking. i have a bone stock z and am only going to add a couple of small mods, pop charger and spacer. this will lean the car out a tiny bit and give me hopefully 12whp or so. but hopefully not enough change to cause the ecu to pull timing.

i guess i'll have to spend on suspension and appearence mods until there is a fix for the ecu.

 

To clarify what you have said the ECU operates in an "open loop mode" when the throttle is around 80% or higher. In open loop the o2 sensor reading has no effect on a/f ratio. However thre ECU has no way of determining what the a/f ratio is. It can be richer than it needs to be and killing power or way too lean causing engine problems..

 

Your pretty much right on with the operation on the ECU. Under full throttle the ECU relies on map for fuel and timing and doesn't rely on the air fuel ratios. Under normal driving it does rely on the air fuel ratio to adjust the injectors pulse duration and timing to give the car optimum performance in mileage and emissions. The service manual states the operations of the ECU. That is why when you put intake and exhaust mods the car will run leaner on a dyno because the ECU is injecting the same amount of fuel under WOT.

 

Has anyone experimented with an adjustable fuel pressure regulator. Such a s the nismos. I would sugest that a car operating at the high end of factory specs for fuel presure would run slightly richer. This would "add" fuel at all rpms/conditions, which is inot deal but a slight bump tuned on dyno with A/F readings might yield a more ideal A/F ratio. Thanks for the clarification of open loop and closed loop I always brain fart on which one is reading of the 02 sensor BTW I meant to start this post in the intake exhaust section. My mistake

 

I have a couple of basic bolt-ons (intake, exhaust, plenum, etc..)

again, this morning I reset ECU and suddenly 4th gear pulls like 3rd... EVERY time I reset ECU after couple months, car feels stronger.

How do you explain this?

I think I'm going to go dyno next month. then clear ecu and dyno again...

 

Yes please do a before and after dyno so we can have actual data. I know some times my car feels slower than usual and then sometimes it feels fast. I have gone to the drag strip when my car felt slower than usual and I still ran the same trap speeds and my ET's were pretty darn close to the my ET's and traps when my car felt fast.

 

Drive a econo box rental for a couple of weeks. The z will feel really fast! A lot of variable effect power intake temps / moisture. (density of 02) coolant temps will effect timing and power. Dyno runs to compare mods should be done at a consistient coolant temp. Voltage at the fuel pump (big stereo causing a loss in HP. Probally not.

 

I've heard on higher volume fuel pumps that a for ever 1volt drop = 10% drop in fuel output... this is why "boost a pumps" work, they provide more voltage to the pumps as some reference source increases (boost).

You do have a little buffer, since most factory tunes for the US market are based upon 89octane for cars that require premium. This allows for some variance in actual octane ratings, and it helps if someone were to put 87 or 89 in their car by mistake. So if you are running 93 you have little more room for mods. I don't know if nissan bases their tune with 89 for sure though.