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Old 12-09-2001, 03:05 PM   #1
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Join Date: Mar 2001
Location: Los Angeles
Default Happy, got some questions for you (Engine management)

Repost: Please understand I am asking the guys in the AFTERMARKET FORCED INDUCTION FORUM about engine management , NOT THE WRX. Please do not move this to the factory forum.


I'm currently running a unichip on my 02 WRX w/ a nice 1818 turbo upgrade and STI injectors. I bought the unichip as a temporary solution as a) it was readily availble b) easy to setup c) relatively cheap. I am now concidering upgrading my engine management to any of the stand-alone or parallel aftermarket ECUs. The one that I believe best fits my needs (street, road race) and my abilities. Basically, I don't need a Motec or high-end Haltech. The other unit I am seriously concidering is the Tec-II, but for me it seems a little expensive.

What throws me off on the Link ECU are two things. 1) It uses all the stock sensors. Are they accurate enough, and why use a MAF when you an change to MAP (a la Tec II) which would allow for better intake packaging and a BOV (although I'm not quite sure specifically what other benefits/issues this might cause). 2) It still uses the stock ignition system (I am assuming this is one of the reasons why you upgraded to a Motec). My car has plenty of turbo and plenty of fuel for more HP, but the ignition just can't handle more timing w/ out detonation. Can you easily ad aftermarket igntion to the Link or even Subee engines in general?

My goal with a new ECU is not NECCESARILY more power (although I'll gladly take some where I can get it). Its an issue of reliability. The delta adjustments of the Unichip are great for the drag strip or quick speed runs, but if you beat on it progressively EGTs go out of control (my guess is the stock ECU is retarding timing as it senses slight knock - even though it never shows up on my knocklink!) I want reliable power that can't cope with weather changes. I want an engine that I can safely road race with.

Oh, and the reason I've posted in this forum is simple. I love the WRX factory forced forum, but I lurk around here a lot and there is a TON of knowledge on these systems floating around (granted not neccesarily for the WRX, but similar applications in RSs) without the hype of the WRX forums. I understand that there might be certain differences you can't account for, but I'm open to yours and anybody elses informed opinions. I am by no means an expert, just an enthusiast.


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Old 12-09-2001, 04:53 PM   #2
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Join Date: Nov 2001

Confused ? I am Don't know WHERE I should be replying to Guess it will be moved to the right place.....

Ok, first to clear up a few points. The Link DOESN'T use MAF, it uses MAP. I, and many others remove the maf altogether.

I don't know "anyone" who has had any problems with the stock ignition. That's not to say that it can't be improved upon, but it seems to do the job. I still use it on my car, and its fine, even at 500bhp ++.

The only time I've had any problems with the stock sensors, was/is, with the Motec. It was VERY prone to "ref", and "sync" errors. These refer to the crank, and cam sensors. There seems to be one or two issues with the sensors sensitivity. I'm not aware of ANY such issues with the Link.

People seem to forget that the POSSUM LINK ecu is not generic, it's design, and software is dedicated to the turbo Impreza, and where some ecu's will have issues with certain arears of mapping, or control, the Link will deal with it much better.

High egt's are normally induced by running too lean, more so than the ignition being out a few degrees. Det' can also be caused by running too RICH, as well as running too lean, but most of the det' issues are caused by people thinking they can just increase the boost, add a bit more fuel, and ignore adjusting the ignition to suit the boost.

One of the problems with mapping, is taking into account the interpolation between each "load" row. EG: Here is a small section of a fuel map, showing RPM column, against LOAD rows.

Row (4). 2~.6 ...bar:rpm.......4000.....4500.....5000.....5500
fuel %................................40.........41.... ......41........42

Row (5) .6~1.0...bar:............42........43...........43 ........45

Row (6) 1.0~1.4 bar:............43........45...........46........4 6

It doesn't matter what the fuel values equate to, just that a fueling of "40" is less than a fueling of "42".

So if you are doing 4000rpm at .6 bar, you may be in row 4 (40), or you may be in row 5 (42). Or if you are at .7 bar, the ecu will be interpolating between row 4, and 5, whilst if you are at .9bar, it will be interpolating between 5, and 6.

So it's crucial to make sure that the fueling is good in all rows, in all conditions, especially at high rmp. The fueling may be fine at WOT, foot to the floor, but lift off just a tiny bit, and it goes lean. It helps if you know where the load points are. This is easy in a re mappable ecu, but I doubt it's so clear with a Unichip.

Remember the stock ecu doesn't run "closed loop" lambda on boost, and even with a fully re mappable ecu, I wouldn't recommend it, unless the ecu has REAL "wide band", with temp' compensation.

The same applies for the ignition map.

I hope this makes sense, if not, I'm sure you guys will let me know

Happy. edited, because the software doesn't like big spaces !! and I gave up.....

Last edited by Happy; 12-09-2001 at 05:10 PM.
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Old 12-09-2001, 05:19 PM   #3

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16 WRX (white)
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You're looking to upgrade your FACTORY FORCED INDUCTION vehicle. This belongs in FACTORY FORCED INDUCTION.
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Old 12-09-2001, 06:30 PM   #4
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