i have a question, on 2nd gen rx-7s now most of us know the secondary injectors " kick in" at 3800 rpm or so...

well im wondering what actually happens when they kick in as far as adding fuel goes.

i have two theorys

1st theory, primarys are flowing more and more fuel up to 3800, then at the magic 3800, they keep flowing the same fuel/and or are still increasing, and the secondarys start adding a bit and then more and more as rpm/load increases.

2nd theory, when 3800 rpm is reached, the fuel load is split, what i mean is at that rpm ,the primarys are cutting back some fuel and the secondarys kick in that amount that was reduced from the primarys, , and then they both continue increasing fuel as the rpm/load rizes....

reason i ask is im tring to figure out around how much extra fuel is going in, now lets say in a normal car you had stock 200cc injectors and you installed 300cc on the stock ecu, at all times the motor would be seeing aproximatly 33% more fuel than the ecu "thinks" is going in.

now using a NA ecu it thinks you have 4x 460cc, but what if you use 2x550 cc primarys and 2x720cc secondarys... you can calculate you would be running about 20% more fuel than the ecu "thinks" is going in, untill you hit 3800, then what would happen exactly??? because you dont know how the fuel load is split between the primarys and secondarys, this would make calculating the amount of fuel actually going in very difficult,

and i dont want anyone saying get a wide band or tune it, thats not what this question is about, i mainly want to know what the ecu does after 3800 as far as which injectors do what amount of the fuel load.......

 

theory #2

 

are you positive?? do they go to a 50/50 load? or what is it?

 

Oh.. man.... Now you got me thinking....

After the autronic, Mictrotech Motec and Haltech manuals........ I'm not exactly sure, but i DID read about it some goddam place a few years back... Now you are going to have me up all night trying to remeber.........

 

haha, im wondeirng what the stock ecu does, just to make sure, i dont think most people look that deep into the stock ecu, they all throw it away for a standalone and never think of it again! lol

 

It's #2, the primarys cut to half and the secondaries take up the other half.

That's what causes "3800RPM hesitation," due to any number of possible problems, the secondary injectors may not start firing on time. The car spikes lean for a moment and the car stumbles since it is only getting 1/2 of the fuel it needs. Take a look at any air/fuel dyno and you'll see the lean spike (on affected cars.)

 

There's no theory here, that's exactly what happens. When the secondaries come on the pulsewidth is halved and all four injectors fire at the same pulsewidth. The total amount of fuel being injected doesn't change suddenly, it's the same directly after the transition as it was immediately before.

 

Good Info..and good reading ..Thanks Gentlemen..I always knew it pays to read everything posted!!..

 

To go into a little more detail...

Primaries are fired sequentially under ~3,800RPM or so.
They alternate firing front versus rear.

At the fuel injector crossover, the primaries and secondaries are all batch fired.
So the pulsewidth is dropped, and all 4 fuel injectors fire at the same time.

That hesitation is typical grounding problems, as the current requirements are suddenly doubled due to all the fuel injectors are firing at that point.
Bad grounding will cause all kinds of headaches due to the sudden increase in current demand.


-Ted

 

thanks for the info thats what i wanted to know

 

Beautiful information.

Do you know if the firing is synced with the eshaft rotation?

-=Russ=-

 

You know....... after diggin through my manuals.. its the Autronic that runs differen't.. all the others stage the injectors by adding the second set and halving the injection time (with stock injectors that is.. ) and then increase from there

 

yep. the CAS signal is used to set the injecotr firing rate and when, the MAF and /or pressure sensor and o2 signal are used to set the MS of injection time.

 

That is correct.
This is called "injector phasing", where you try and match the firing of the fuel injectors to the intake timing.


-Ted

 

Most people just call it injection timing.

The ECU also varies the injection timing with engine speed. At less than 3,000rpm fuel injection occurs at 95deg BTDC, and then it starts to be retarded as engine speed increases, back to 185deg BTDC at 5,000rpm and above (info taken from the 1986 Factory Training Manual).

 

Is this factory training manual available online anywhere? It sounds like it contains a wealth of fascinating information.

-=Russ=-

 

yeah show me where i can find it!! id love to read it

 

Jesus, I thought you were a well informed enthusiest... do you memorize this stuff in your free time? You're practially a bottomless pit of FC knowledge.

Does Mazda still have these training materials, or would I have to become an employee to get them?


RETed: I wish I had spare time when I was in Hawaii...

 

I would be very interested to see one of these training manuals.

 

It's not about memorising everything, just keeping lots of reference material handy. And since most of it is on my computer, and the forum is also on my computer, it's pretty handy.

The Training Manuals were to inform Mazda techs of the major design changes between models. The one I have covers Australian, NZ, European and Middle Eastern 1986 models, but a lot of the info is common to all FC's. If have a paper copy I borrowed from a mechanic mate. The chapters are broken down just like the FSM and I've scanned the chapters that were of interest to me. I can scan the rest and e-mail it to anyone who wants it (PM me your address) and if someone wants to host it they're more than welcome. Jjust don't expect it in a hurry since all have to do the scanning and sorting at work and I'm damn busy!

 

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