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Old 01-23-2009, 12:31 PM   #1 (permalink)
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My car is too eager to switch to open loop

I've had my scangauge for a few weeks now, and I've noticed a few undesirable things my engine management computer does, especially when it's cold.

Most annoying is the very high idle until it warms up. I show an open loop idle, 1500 rpm, and 1gph for the first minute or two of driving. Once it gets vaguely warm, I see open loop, 1000 rpm, 0.50gph. This is still not as desirable as the closed loop, 500rpm, 0.25gph that I've come to expect. I often see the 0.50gph idle with the coolant temp at 195F while I'm trying to pulse and glide. I run 0W30, so I'm confident it can idle lower especially while it's cold. Can I force it into closed loop idle?

There's a seperate issue: whenever I open my throttle more than, say, 1/3, it goes into open loop. Yeah, I know, welcome to the real world. Still, can I keep closed loop for slightly larger throttle aperatures? What if I mod the TPS?

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Old 01-23-2009, 12:37 PM   #2 (permalink)
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Quote:
Originally Posted by RobertSmalls View Post
Most annoying is the very high idle until it warms up.
Get a block heater!


Quote:
Can I force it into closed loop idle?

There's a seperate issue: whenever I open my throttle more than, say, 1/3, it goes into open loop. Yeah, I know, welcome to the real world. Still, can I keep closed loop for slightly larger throttle aperatures? What if I mod the TPS?

Even if you're able to, you do not want to. The engine is running as it should.
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Old 01-23-2009, 01:45 PM   #3 (permalink)
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Sure I want to modify it. The engine management software is desperately afraid of stalling, and it's built to endure things like 10W30. I want my ECU to live on the edge a little.



This chart, from a paper by Subaru, shows my engine's BSFC (in grams of gas per horsepower-hour), which is what I need to minimize to get the most oomph out of a gallon. The chart leads to two conclusions: revs bad, using the engine near its capacity at a given RPM good. The latter is achieved with throttle.

I know the above plot represents what the engine is capable of. What I'm not sure of, is whether their test used the same ECU I have. Oh, if I only had a dyno and a laptop-based OBDII data acquisition setup.
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Old 01-23-2009, 01:51 PM   #4 (permalink)
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And then it occured to me: I do have a dyno, in the form of a 600' ascent at 10% grade. See how much fuel it takes to get to the top at top speed in 5th gear, repeat the test in other gears with cruise control. I'll see if I can get out to the hills this weekend.


Last edited by RobertSmalls; 01-23-2009 at 02:00 PM..
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