I have an S4 racecar with S5 engine internals and have blown up 4 engines due to a lean running condition that I cannot solve. I could reprogram the ecu to up the injector duty cycle but down the road while initially harder will make engine swaps much easier. I want to swap all the electronics in the car to run a complete S5 motor and ECU. The engine harness is straightforward but I was wondering what else needs to be swapped to make it work ie the ignition harness, fuel pump relays. The car has no emisions and very little dash to work around and already is mostly S5 ie intake w/o 5th, 6th ports, S5 tranny, S5 fuel tank. Basically what I don't know is what harness other than the engine harness is necessary to be able to use the S5 ECU? I do not want to start over with a S5 car because mine is complete with rollcage, suspension, fire systems, harnesses on and on. I have a number of complete S5 parts cars for all the parts.

Any advice or direction to post is very much appreciated.

Jamie

 

if you don't have a FCD then thats the first thing you did wrong

 

unless the FCD fits inside the ECU box it is not legal for my class.

 

what are you racing then that doesn't let you run a FCD with a stock ecu, i'm not a uber rx7 boy but i do know not having one lets you lean out and blow motors.

 

How would the FCD do anything with a non turbo car? Very rarely have I seen a non turbo car overboost and go into fuel cut.

 

A DER DER DER on me... i sall lean and motor blown and the words n/a left my mind. sorry

 

Dude,
You really need to PM me! I am undergoing exactly what you are about to start!
Think I'm joking:
https://www.rx7club.com/rotary-car-performance-77/s5-s4-wiring-harnesses-question-engine-swap-536779/

Regards,
Crispy

 

Personally I think you should find the real cause of the problems, because I highly doubt doing this is going to help you at all. A compression increase of 3% is not going to cause you to run lean, particularly when the stock mixtures are so rich, so I can't see an S5 ECU solving your problems.

But if you really want to do this, a study of the ECU info in the S5 FSM will give you all of the answers you need. Look in the Fuel System and Wiring Diagrams chapters. All FC ECU's have two plugs from the emission harness and one from the front harness. Swapping in the S5 emission harness is no big deal but it would definitely not be worth the effort to swap in a front harness, particularly since you really only need six of the wires on it. The ones you need are the two power feeds and the four coil wires. You'll need to cut that plug (22-pin) off an S5 front harness and wire it onto yours.

 

NZConvertible, Thank you for the harness advice, that's the approach I will take if I go that direction. I would like to hear further as to why you think it will not help and that I need to find the root cause. I have dyno tuned many s4 and s5 cars and without exception all the S4 cars (with S5 motors) run lean(some stay in the high 13s% but mine and others go into the 14s% at rpms above 7400ish and all the S5s run very rich (never exceeding high 12s%). I assumed (feel free to correct me) that the injector duty cycle driven by the ECU was set higher on the S5 than the S4. Fuel pressure adjustments make huge differences on S5s as compared to the S4. I was assuming the ECU map was very different on the S5 ECU for the simple reason that the S5 came out of the factory with more HP but the same injector size so the designers must have upped something to flow the extra fuel, no? I've heard that the duty cycle for the S4 is 58% but I haven't heard what the S5 is?

My S5 engined S4 electronic car has had every fuel component and sensor replaced at least once ie blueprinted injectors, replacement ecus, tested and replaced temp sensors, boost sensor, MAF sensors, MAFs, engine harness, 3rd gen and walboro fuel pumps, new filters. The car is an SCCA ITS car and has a CAI and a tuned exhaust, no emmisions and no 5/6th ports. Nothing is ported or polished inside (illegal for class). S5 rotors,flywheel and front ctrweight. My fuel pressure holds rock steady at any pressure I choose. The stock FPR has been removed and pressure is controlled by an AEM adjustable.

 

If you've had experience tuning engines then you should know that injector duty cycle is not "set" to anything. It is a constantly and widely varying figure dependant on injector pulsewidth and rpm. The "fixed" 58% number is a complete myth. If anything it's just the maximum IDC reached in stock form.

I would've though you'd also know that an AFM-based system does not require major retuning for such a small increase in power. The amount of fuel injected a dependant entirely on the measured airflow.

You're talking as if the S4 and S5 engines are fundamentally different, but they are actually mostly the same. Most of the extra power comes from the ability to "tune" the manifold for two different rev ranges (VDI). Why would an S5 engine need more fuel for the same airflow? That makes no sense. An S4 engine modded to make 160hp would have the same fuel requirements as a stock 160hp S5 engine. And why would fuel pressure make a difference? The fuel system is basically the same for both models.

 

Thanks, tuning is probably an overstatement as the engines are basically stock but I have tested many different exhaust designs, ignition timing, fuel pressure and AFM adjustments.

Are you saying that a S4 ecu car with a S5 longblock (making 180 rwhp) will have approximately the same AF ratio as a full S5 car (making the same 180 rwhp) at 8000 rpm?

Maybe I am fundamentally misunderstanding something but given that both cars would have their AFM at full open at 8000 rpm something is telling the S5 ecu to send more fuel given the richer runs of the S5s that I have seen.

Backing up, even totally stock cars, with the S4 at 146 fwhp and the S5 at 160 the S5 needed to get more fuel to go with the better airflow so the S5 must have a richer map, no? Or are you saying the difference was so small they have the same map?

I really appreciate your help on this.
Jamie