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Old 06-12-2008, 09:37 PM   #1 (permalink)
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EOC fuel usage ?'s

I have heard that when you start your car (cold) that is uses up to 6 times the amount of fuel that it uses in normal conditions until it warms up and goes into closed loop. If you do an EOC with a fully warmed up engine, and then start it with the clutch, does it still go through this routine? and if so how long does it take to get back into closed loop roughly? I ask because even when the car is warm and I do an EOC, whenever I pop the clutch to start, it seems to start just like I started it with the key and idles high for a while before it settles down. Maybe 30-45 seconds or so. Anyone have any info, links, ideas here. Any input would be appreciated, thanks.

I'm just trying to do a little math and see if it would be more beneficial to P&G with engine braking or EOC. with EOC I get 2-3 more seconds of glide time when doing my 60MPH-40MPH ect. P&G. But if I'm using more fuel starting it after an EOC every time then it wouldn't be worth it. I suppose I can do a little A-B-A testing but if anyone has looked into this before, that would save me the trouble

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Old 06-12-2008, 09:45 PM   #2 (permalink)
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Quote:
I have heard that when you start your car (cold) that is uses up to 6 times the amount of fuel that it uses in normal conditions until it warms up and goes into closed loop.
That's a bit of a stretch. I'd say 1.5x is more like it on the coldest of days.

Quote:
If you do an EOC with a fully warmed up engine, and then start it with the clutch, does it still go through this routine?
No, the ECU is aware of coolant temperature and the O2 sensor is already at operating temperature.
Quote:
and if so how long does it take to get back into closed loop roughly?
Almost instantly.
Quote:
I ask because even when the car is warm and I do an EOC, whenever I pop the clutch to start, it seems to start just like I started it with the key and idles high for a while before it settles down. Maybe 30-45 seconds or so. Anyone have any info, links, ideas here. Any input would be appreciated, thanks.
Solution 1: Put the engine back to work so it won't idle.
Solution 2: Take idle control away from the ECU by unplugging the IAC.
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Old 06-12-2008, 09:47 PM   #3 (permalink)
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It won't go through the same length of open loop enrichment that you experience from a cold start, because the ECU uses the coolant temp to set that condition.

My car remains in open loop for three seconds after a warm clutch start. But what you described makes me think it may differ from car to car.

Quote:
I'm just trying to do a little math and see if it would be more beneficial to P&G with engine braking or EOC
P&G with engine braking isn't P&G, and I'd be surprised if you weren't getting lower fuel economy than if you just cruised at a constant speed.

Quote:
I suppose I can do a little A-B-A testing but if anyone has looked into this before, that would save me the trouble
Sounds like a plan.
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Old 06-12-2008, 09:50 PM   #4 (permalink)
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Quote:
Originally Posted by JohnnyGrey View Post
That's a bit of a stretch. I'd say 1.5x is more like it on the coldest of days.
Maybe depends on the car, but mine is @ 3x normal fuel consumption rate immediately after a cold (-7C) start (but not for long):



Mini-experiment: cold start fuel consumption and warm-up time

I haven't repeated this in summer weather. Probably should...

And of course the actual warm up time is much shorter than that, because I never idle my car to warm it up, and usually use a block heater
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Old 06-12-2008, 09:51 PM   #5 (permalink)
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Thanks for the input.

Quote:
Originally Posted by JohnnyGrey View Post


Solution 1: Put the engine back to work so it won't idle.
Solution 2: Take idle control away from the ECU by unplugging the IAC.
I do actually put the engine back to work, I only happened to let it idle one time when I had to brake right after clutch starting the car and I noticed it idling high. Then I checked it a few times (on different trips to make sure) after and it did it every time. It got me thinking that if it was using more fuel, then even if I was using the throttle, I would still be comsuming more fuel... I AM glad to hear that the 6x is a stretch, that seemed incredibly high to me. But then again, I was thinking of a choke on a carb and what that does to the A/F mixture for a cold engine, so I thought it might be a possibility.

Any side effects to unplugging the IAC?.. other than maybe a little trouble holding idle when really cold.

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