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Old 06-13-2012, 06:04 PM   #1
eg33GC
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Member#: 206851
Join Date: Mar 2009
Chapter/Region: MWSOC
Vehicle:
99 V4
EJ20K RS

Default Lean tip in EJ20g 4plug ecu discussion

There is a very serious problem in the JECS 1992-1996.5 4 plug ecu programming.

The what:
The ecu has a lean throttle fueling tip in, meaning that when you so much as poke the throttle open, the afrs rocket upwards. For instance, my personal car will go from 14.5:1 at 2500rpm at under 10* load to 17:1,16:1,15:1,14:1,13:1,12:11.3:1 finally after about 3 seconds. Pmugabi reports his is around 2 seconds.
500ms is too much imo.

The why:
Hard coding in the ecu (somewhere), is forcing fueling trims up on WOT initialization. The most comprehensive ecu definitions known to myself and pmugabi are from ecutune's ecutuner program (freeware www.ecutune.com) do NOT include a value somewhere in the easily modifiable eprom locations (8000-FFFF)
The problem in my opinion arises from my lack of understanding of how to find or alter this code. I have tried to counter it by modifying fuel cells surrounding the projected rpm/afr/load, but it doesn't help. I also do not run a bypass valve, so my longer effect may be pointed towards that as well. Logically, someone with an atmospheric bypass valve should see the opposite of myself without. However, I haven't had a bypass valve to test.

Implications:
This is dangerous. Especially since we have a unique large bored, short stroked, playdoh equipped bearinged engine, this lean WOT tip in should be taken with extreme caution.
Drag racers like myself and 69360 are most at risk, but autoxers and hpde people should also take heed.

What we should collectively do:
There are some bright people in our section, a pair of them at least intimate with programming. The open source computers have this defined somewhere, so there is hope that somebody smarter than I can find it.
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Old 06-13-2012, 07:14 PM   #2
rob
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Vehicle:
2000 RS-Ej20G
It tastes like burning

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Hmm, I don't think I have ever noticed this, but it could be that I wasn't looking. I certainly do not see any knock activity under these conditions. I have a couple ideas what this could be, but need more info.

Do you have any WB logs to show? What manifold pressure is this at? Is it the same behavior at higher RPMs?

-Rob

Last edited by rob; 06-13-2012 at 07:28 PM. Reason: grammar is hard
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Old 06-13-2012, 07:21 PM   #3
rob
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It tastes like burning

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Is this with your modified injector scaling?
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Old 06-13-2012, 08:50 PM   #4
eg33GC
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Join Date: Mar 2009
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99 V4
EJ20K RS

Default

It is usually at low load, low rpm, 5-20 vac. I can do a LC1 log soon.

Stock inj scaling. Pump gas, 550s. It might be because of the difference between your "perfected" 550 tune and my own 550 brew. If you want, send me your rom file, since I destroyed your bin many moons ago
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Old 06-13-2012, 09:00 PM   #5
rob
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If you can, log RPM and MAF voltage at the same time. Do a run with and without the O2 sensor plugged in.

-Rob
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Old 06-13-2012, 10:36 PM   #6
69subaru360
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1995 WRX
1998 2.5 RS

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Mine never did with 6k or Rob's chip.

My drag racing days are over, it's more of a backroads fun car now.
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