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Old 10-10-2012, 12:42 PM   #1
TheNewThatGuy
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Member#: 148041
Join Date: May 2007
Chapter/Region: International
Location: Germany
Vehicle:
2000 Rally Impreza
Blue and Gold, baby

Default Removing backup power from ECU?

I have an idea I've been heavily tossing around the last day or so, first let me explain my problem, and I will get to my proposed solution in the title.

With my ej251 in my 00 Impreza, I have quite a bit of modifications on it. Most relevant to this issue being a "9" lb flywheel (measured at 12) and the most aggressive N/A cams Delta would make me. My warm, stock idle (600ish) is garbage, but is butter smooth by 1000. Which I can raise to with ecuexplorer. Anyways, from doing some reading years ago, the combination of cams and a lighter crank (minus over 20lbs from the flywheel - also had a lighter pulley, saw no gain and removed it), could cause misfire codes due to the cam/crank sensors going out of sync/sending "false" signals, in extremely simplified terms.

The only real options are to raise the idle and lash the valves a little looser. These did nothing. I also have a Crawford SRS-30 reflash, as there is virtually no support in regards to tuning this ECU, so it's the best match I could find without going standalone. It seems my setup is just too aggressive. Then a thought occurs.

As my misfire codes appear, if I just reset with a code reader, which only clears the current cycle, then the codes come back quick. I'm talking around 50-100 miles. Often at idle (which is not smooth, because I get tired of hooking up a laptop to bump it) Or prolonged steady rpm. However, the initial code on a true reset; clearing the memory by removing power, takes around 500-1000 miles to trigger.

This brings me to the ECU's "learn" function. I'm not the only one that thinks due to this function, having a reflash tune the modified base maps and tables will be unlearned by the natural process, rendering them pointless, as time goes on. Obviously my modifications do not get along with the base ECU parameters that the ECU intendeds to see from the sensors, regarding the engine. Which makes sense, because it is not a stock engine. Now, on a stock engine with a stock tune, I would not recommend this if someone was saying they were constantly getting the same codes, because this would just be ignoring the issue, but given these circumstances, might it be a good idea to cut the back-up power? This would force the ECU to "start from scratch" nearly every time I start it. That would mean start with the actual tune, which would theoretically be a better running engine for what I have done, all around. Gas, performance, etc...

So, other than allowing me to actually retain my tune, it would eliminate these "nuisance" codes. I don't datalog, so I'm not sure if misfire codes are "safe" codes, but by the point they appear, the ECU has learned itself into a pig-rich, unresponsive mess.

Thoughts?
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Old 10-10-2012, 12:50 PM   #2
eg33GC
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Member#: 206851
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56 Belair
Pro Street

Default

Link G4,
or get a swap.

Backup power just keeps the referenced run time rom info alive electronically, it won't help anything but maybe your rough idle (For the first half hour, etc).
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Old 10-10-2012, 03:26 PM   #3
TheNewThatGuy
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Location: Germany
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2000 Rally Impreza
Blue and Gold, baby

Default

I have a swap. I have a EG33, but I bounce between it and the EJ251. I have zero interest in a turbo EJ.

I know the resources are limited with the N/As, that's why I'm posting. Are you saying keeping or removing the backup power connection will help with the rough idle? Because honestly, nothing helps with the idle. The engine cannot maintain static RPM below 1200 regardless of ecu fuel/timing. I'm not worried about the idle, just the misfire codes and it learning to run like ****.
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Old 10-10-2012, 10:55 PM   #4
pmugabi
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Seems like removing the backup power should work for you. And if you pull out the pin from the ECU plug instead of cutting it, the mod will be fully reversible.

Edit: Is it possible that simply removing the O2 sensor will fix the issue? It sounds like the car's log term fuel trim is being set wrongly. Removing the sensor will prevent this from happening.
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