20FS

how much power will an ECU from a jdm famila give me?

Traveler

Considering that it won't work on your car, not a lot! They have different pin outs and wiring harnesses on the JDM cars. This has been discussed on the board before especially for the guys that have already installed the JDM FS-ZE motor. The MP3 ECU will connect right up though and it will give you better throttle response and a couple more ponies. Kind of spendy though. Wait until AEM comes out with the plug and play or get a good piggyback that will control fuel and spark.

jstand6

I've heard many times that while a piggyback system will improve throttle response and power at part throttle, the Mazda ECU will override at WOT with it's preset settings. Is that true?

Talking to the technicians at Injen, I found out that Mazda's generally respond poorly to mods because the ECUs are extremely hard to get around and override, or attempt to override, changes that are made. I remember on a '91 Escort GT I used to own (gawd, I miss that car...), I tried to manually change the ignition timing by turning the distributor and watched in horror as the ECU immediately adjusted... I probably should have expected that!

-Jerry

Eric F

Your right, but you have things backward. At WOT, the ECU goes into open loop mode (uses preset ignition and fuel maps stored in the ECU's memory), which is easier to make adjustments to with a piggyback system. In closed loop mode, the ECU will try to negate the effects of tuning with a piggyback system.

obender66

Ok, as much I understand piggy back system able to change values should modify ECU OUTPUT signal at WOT and not input signal as Apexi SAFC does, for example?
Alex

jstand6

Now I know where I've heard that. In the Forum FAQ. At WOT, the ECU has factory presets which cannot be adjusted by a piggy back system. Only at part throttle can more power and throttle response exist. At WOT, the ECU uses preset ignition and fuel maps regardless of system inputs. Of course, if WOT is going to be the same as stock, why get a piggy back system?

-Jerry

Traveler

Correct to a degree. At WOT and past a certain RPM, the computer reverts to look up tables and uses set values based on RPM. This is the time when a piggy back will be able to intercept and control output to the injectors and adjust the timing. Since the factory ECU is outputting set values, it will not try to compensate if you change the injector output signal. If you want the mixture leaner, just intercept the signal (usually at the ECU) and output a signal that will decrease the injector open time. If you do this at part throttle, the computer will compensate and will just try to adjust the mixture to whatever the computer wants to see.

So, in review, WOT is the ONLY place that our ECU's will not try to compensate for tuning tweaks from a piggyback. I've talked to several places and they say that our ECU's are one of the hardest to tune with since they are extremely willing to compensate for anything outside the required parameters. Since our engines have a cam position sensor as well as a crank sensor, they will generate a check engine light if you try to intercept the crank trigger and try to fool the computer into thinking that the timing is retarded. This is a good way to get advanced timing on other engines, but ours will see an error between where the crank is and where the cam is and generate a CEL if they are too different. It might be able to be tricked into advancing the timing a couple of degrees but I haven't spoken to anyone that has tried it.

Since our timing curves are just about perfectly suited to forced induction, I'm just going to put a blower on the motor, leave the ECU alone and tune the fuel with a stand alone additional injector controller and a fuel mixture meter.

The only way to really tune the ECU on these engines is to yank them and put in a stand alone. This of course generates a bunch of other problems with having to tune it from the ground up as well as not being OBD-II compliant. AEM is rumored to be making a plug and play computer for our cars. If that happens then it will make tuning a lot more precise and flexible. The list price would be about $1800 until warehouse places start to stock them and the price is reduced from them.