Modding ECU for 95-99 Subies - Rev limit + idle speed change

[fastenova]

I am working with some other members on NASIOC to document the process of reclocking our ECUs (overclocking, really) to bump the idle speed and rev limit. Please feel free to read and give any input you may have.

http://forums.nasioc.com/forums/showthr ... ?t=1736906 (http://forums.nasioc.com/forums/showthread.php?t=1736906)

[xXGTBspecXx]

if you find out how before i get a EM for my wagon lemme know.

[Huffer]

If you read the thread he's already got it done, just hanging on the IACV to avoid the lopey idle. So if you don't mind that, then it's a perfectly viable option.

Anyone who lives in a temperate zone could do it right now... the rest of us have to wait.

[keltik]

Hmm might have to pick up a spare ecu and give this a shot. Would be cheaper than attempting to reflash mine.
Im still making power at 6500rpm and i know the valve-train can handle more :twisted:

[fastenova]

Just wanted to update you guys... I found out that the electronics "guru" who helped me identify the crystal was wrong (just a knowledgeable guy in a local shop) and gave me much too slow of a frequency!

I've updated the thread with the new information, but I've got a slight problem I'm working on fixing. The IACV issue is gone (actually never was there), and the car idles around 800RPM now, and revs up to 7K (that's all I've done so far), but is running crappy during closed loop. Like, really crappy, very lean at times, undriveable crappy. I will update here and on NASIOC when I figure out why. I've got some ideas but want to figure that before I advise anyone to move forward with this, as I don't want to cause anyone problems.

[fastenova]

On that note, does anyone know of differences in sensors, and/or programming changes in the ECU between 1997 and 1998 motors? Both ECUs are from Legacies with 2.5L motors, originally automatic (5mt swap in my car). If there are any small differences between MAF or EVAP or other systems that could be causing my problem.

I know the 1998 vehicles had a fuel temp sensor in the fuel tank, and 1997 doesn't, so the ECU reports a fuel temp sensor error when using the newer ECU on an older car.

Anything else?
Thanks,
Aaron

[impreza_GC8]

Props for working with some of the older Subie ECU's but why you'd want to raise your rev limit I just don't understand. Our engines stop making power far before redline and the valvetrain isn't built for a whole lot of high-rpm action either (depending on your heads). I've got '96 HLA heads and I still worry about them even at stock redline.

[keltik]

Well in my situation im making peak power at 6200rpm and the power curve holds steady right up to redline. However the limiter kicks in at 6650rpm so when i shift im starting the next gear much lower down the torque curve than if i could wind it out to 7k.

The JDM non turbo EJ20 with HLA's and quad cams has a factory rev limit of 7,500rpm as do the turbo models.

[fastenova]

Props for working with some of the older Subie ECU's but why you'd want to raise your rev limit I just don't understand. Our engines stop making power far before redline and the valvetrain isn't built for a whole lot of high-rpm action either (depending on your heads). I've got '96 HLA heads and I still worry about them even at stock redline.

Thanks for props =]

My car is far from stock, although internals are mostly the same. I'm running Delta cams (DOHC motor) and have found that my engine pulls hard all the way to redline, whereas with stock cams power drops off near 6000RPM. I've been told by others in the Subaru community that the stock top end is good in excess of 7500RPM.

The single biggest reason for the modification is wanting to bump the idle. The idle is lumpy to the point that it sounds unhealthy. I don't need to raise it much to make it run smoothly, but 700RPM is just too low for these cams to be streetable, to me. The 800RPM idle it's at now feels silky smooth in comparison, and it doesn't fluctuate.

As far as the redline, I probably won't go over the stock redline of 6500 often. Driving very hard, I usually shift between 6300-6500, as that puts me right in my powerband in the next gear. Perhaps if I get stiffer valve springs and lighter valvetrain, but there are plenty of people out there with a valvetrain ready to go to 8K and the stock ECU is holding them back. With a piggyback, correctly tuned, and this modification, one could argue that it defeats the need for a standalone EMU on a modified street car.

Pure race car, well, that's a different story, but I still drive my car every day... And I love it :smt029

[jey]

The single biggest reason for the modification is wanting to bump the idle. The idle is lumpy to the point that it sounds unhealthy. I don't need to raise it much to make it run smoothly, but 700RPM is just too low for these cams to be streetable, to me. The 800RPM idle it's at now feels silky smooth in comparison, and it doesn't fluctuate.


I wonder if you can't bump the idle a different way? I think there is an idle adjustment screw on the throttle body. You have to adjust your TPS also in conjunction but that still is hardly a big effort compared to your current experiment :)

[subba]

Well in my situation im making peak power at 6200rpm and the power curve holds steady right up to redline. However the limiter kicks in at 6650rpm so when i shift im starting the next gear much lower down the torque curve than if i could wind it out to 7k.

The JDM non turbo EJ20 with HLA's and quad cams has a factory rev limit of 7,500rpm as do the turbo models.
n/a is 7k turbo is 7500

[fastenova]

I wonder if you can't bump the idle a different way? I think there is an idle adjustment screw on the throttle body. You have to adjust your TPS also in conjunction but that still is hardly a big effort compared to your current experiment :)

There is no 'idle adjustment screw' on the TB. The idle is controlled by the idle air control valve, or IACV. The ECU will target a fixed RPM (700 RPM in my case) no matter what. That's what's programmed into the ECU.

You can adjust the throttle opening, but that takes away some of the flexibility of the ECU to control idle, and often times it will learn around that and just not open the IACV as much, to try to return to the programmed idle speed.

This is not a good way to do so if you still want the car to idle well at all temps, loads, etc.

[jey]

There is no 'idle adjustment screw' on the TB. The idle is controlled by the idle air control valve, or IACV. The ECU will target a fixed RPM (700 RPM in my case) no matter what. That's what's programmed into the ECU.

You can adjust the throttle opening, but that takes away some of the flexibility of the ECU to control idle, and often times it will learn around that and just not open the IACV as much, to try to return to the programmed idle speed.

This is not a good way to do so if you still want the car to idle well at all temps, loads, etc.

You're right, totally wrong to call it an "idle adjustment screw" - I called it that because I disconnected my IACV so that was my "idle adjustment" for a while :lol:

That said, I wonder if you can adjust that throttle opening enough and take away enough of the flexibility from the ECU to accomplish what you're trying to do. Yes, the ECU will just completely close the IACV to try to return it to 700 rpm but if the effective idle speed ends up being 800 rpm just on the throttle opening alone and the IACV closed you will get your 800 rpm idle. But then as soon as you turn on the A/C it will drop to 700 again... so like you said, this technique is suboptimal.

[fastenova]

suboptimal.
key word!!! :grin:

Then again, if I can't get my car running properly with the faster crystal, that's suboptimal too! I wish I knew enough about hardware to just dive into the ECU programming and figure it out so we could just flash a new ROM =\ That would by far be the best way to do this!

[jey]

As a last resort you can run standalone EM. I wonder if you'd get the most power out of the upgraded cams with the stock EM anyway, low idle or not.

[keltik]

Opened up my 2002 H6 ecu and it appears to have 2 crystals. Neither have clear frequency markings on them so i didnt bother trying to solder anything new in.
Now working on hacking the ECU with my tactrix cable to see if i can change things that way.

Otherwise just going to wait untill i can put in an aftermarket ECU