blazer1313

So I've been searching for about 2 hours now wading through the archives and found some decent stuff about the upgrade from S3 (gslse) to '88 N/A ECU and related parts. I've already got the S4 UIM/LIM working with my S5 modded/rebuilt block and S3 injection....(I know, Frankenstein). At the time of the swap I didn't have time to convert to the S4 ECU injection system but may be coming into some $ in the future so I'd like to know some info. I was told that its no different than swapping in a TII so I looked at the 17 page TII swap only to find that the links are dead and most of the pics are too.

All I want to know is where to find a writeup on making the driver's side harness since it was also listed that you did not need the mile long harness under the FC's dash only a few for the coils, fuel pump relay (is that even needed for the SE?) and the CAS.

Also after the conversion will the stock guages still work in my SE?

Looking for people who have actually done the swap (turbo or N/A)

Much apprciated
Nate

j9fd3s

iTrader: (3)

yep you're right, it basically is just like doing a t2 swap, so you're best off sitting down with both wiring diagrams and drawing it all out.

most everything is on the engine harness and runs from the ecu right to whatever (injectors, sensors, etc)

the big hookups are powers, grounds, and since the FC ecu controls the ignition, the wiring for the fc coils.

all of the stock guages will work, as none go thru the ecu. the tach is run off the trailing coil in both cases, its just a matter of hooking it to the right wire.

Rx-7Doctor

iTrader: (13)

If you look at the top of the page, you will see the most recent archived thread. :-)

Also steve84gsTII did a recent post on a thread about this also.

blazer1313

ya i looked at it. guess it will make more sense when i do it. i also seached for that user and it came up with nothin. I know he's here I just can't spell the name right or somethin. Was just lookin for help from ppl who have made this "6 or so" wire drivers harness

Rx-7Doctor

iTrader: (13)

https://www.rx7club.com/1st-generation-specific-1979-1985-18/i-need-help-wiring-harness-676806/

steve84GS TII

Here I am!....grins....

The S4 needs only 8 wires on the drivers side ECU harness,to run at the bare minimum.Those are the 4 wires to the CAS,the one wire to the leading coil and the 3 wires to the trailing coils.Thats all between the ECU and the engine components,except of course for the big passenger side harness.

Of course there is a bit more involved than that,since you still have to mount and wire the FC underhood fuseblock,the FC main relay and the FC coilpacks themselves.The wiring for all that is independant of the ECU though,since the fuseblock and relay provide the high amperage items(injectors,coils,solenoids,fuel pump) with their actual power.The ECU just switches the grounds from those items on or off, through the smaller,colored wires coming from the 3 yellow gangplugs.

blazer1313

excellent! I've already replaced my old style wire fusible links with new style block style fusible links. Besides that I need a main relay huh for key on high amp power to the ecu..ok makes sense.

Second question is do you think it's worth it to convert from the S3 to the S4 injection/ignition? I'm currently running S4 leading through an Accel 300+....slight improvement.

Also for an N/A is it worth upgrading to the power FC and commander using this S4 setup? Can't you program the injection rate and ignition curve? OR what's the best version of ECU for the S4 for M/T?

Thanks, you've been a great help!

steve84GS TII

If Im not mistaken....I could be......the Power FC is only readily availble for the S5/S6 engines.I had heard that S4 versions are very hard to come by.FD guys need EFI tuning because they have speed density EFi which cant adjust for ANY mods that effect airflow.....even bolting a muffler and cone air filter can blow up an FD.

There is little reason to NEED to mess with the injection pulsewidths on an S4-S5.Its a metered air EFI system,which means that any mods you make that improve airflow in or out....(exhaust,porting,intake) are going to be measured by an increase in the AFM's door opening.So long as you stay within the mechanical measuring limits of the AFM,the ECU will have maps to feed your engine.The TII is somewhat of an excepetion to this,since its very easy to move large amounts of air with a turbocharger,and compressing/heating the air increases the odds of detonation.I myself,run larger secondary injectors in my S5 engine,but still use a totally stock ECU,timing,injection pulsewidths.....while makeing about 300hp at 14psi.

In stock guise,the EFI is set very rich,and as we all know,its a leaner mixture that will make more power.That,coupled with the fact that its quite hard to get an N/A rotary to detonate,means there is little reason to worry about tuning an N/A rotary when on the stock ECU.If your ever going to make big enough mods that you need in-car tuning,the stock EFI isnt going to be cutting it anyways.

2nd gen style ignition is leaps and bounds ahead of the 1st gen system,but it can easily be duplicated with a direct fire/3 coil setup that uses the 1st gen distributor.You can also use an FC leading coil for direct fire on a 1st gen.Youll have wasted spark/direct fire just like the FC,but the trailing(which doesnt really count for squat anyways) will still have to run through the 1st gen distributor cap.

Theres not a whole lot of gains to be had from going from GSL-SE EFI to the S4 EFI.....its practically the same system,except for the staged injectors.For the most part,the S5 EFI is the same system too,albeit with some refinement to the metering systems and processor speeds.....and it has a REAL diagnostics system with a check engine light.

The main relay doesnt actually send any power to the ECU,it feeds high amperage items like the coil,injectors,solenoids and fuel pump DIRECTLY.....from the relay to those items.The ECU simply handles the switching of the grounds for those items,thus it only has to handle a small amount of juice when it does its thing.Thats almost the ECU's only function.....as a multi-function,ground switching station.

j9fd3s

iTrader: (3)

power fc is setup out of the box to run a stock fd, an N/A s4 setup is so far different, you'd have to do as much tuning as you would running any other ecu, PLUS the pfc is harder to tune, because you dont have the apexi software to do it with.

plus the power fc is wired up to the fd, which is a lot different from the s4...

blazer1313

so a 2 staged injection system and the direct fire trailing coils is all I'd be gaining since I already have it for the leading...we're talking 15-20HP huh maybe more...thats prob with my large S3 injectors used as the secondary injectors in the S4 setup...hmm

steve84GS TII

Most of the power gains of the S4 FC engine over the GSL-SE came from juggling port timing, along with the changes to the intake manifold,exhaust system and the larger AFM/throttle body.The staged injection allowed for a leaner/smoother idle and cruise, since smaller 460cc injectors could be used at longer pulsewidths than the big SE 680cc units......but it also introduced the dreaded 3500rpm stumble that FC's are famous for,when the secondary injectors come online.

The S5 took it a step furthur with a bump in compression,faster electronics and the VDI intake manifold to work in conjunction with the 5-6 ports to boost midrange torque.