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Old 04-07-2007, 08:30 PM   #21
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Quote:
Originally Posted by SVOboy View Post
Engine braking = complete fuel cut.
If that is the case, why does my scangauge still read ~0.3 GPH when I do engine braking?
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Old 04-07-2007, 11:53 PM   #22
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Peakster -

Quote:
Originally Posted by Peakster View Post
If that is the case, why does my scangauge still read ~0.3 GPH when I do engine braking?
I see similar behavior on my ScanGauge. What I read on saturnfans.com is that for my drivetrain, fuel does not completely cutoff. It goes down and down, closer to 0, *but*, then the RPM gets to the "idle RPM", the fuel is restored, because the ECU/PCM never wants to go below the idle RPM. Here is where I read it :

Negative Fuel Trim...Constant
http://www.saturnfans.com/forums/showthread.php?t=89959
Quote:
Bigdaddy94sc2 says :
For STFT to drop when slowing down is normal, due to decell fuel cutoff. 25% is the max it can go to, then it goes into decel fuel cutoff when it sees brakes applied, speed decreasing, and no ABS activation. It doesnt totally cut fuel, but darn close.
Other drivetrains are much better at this and can be very thrifty about cutting fuel when the right combination of driving events appear to the ECU/PCM, i.e. a certain combination of "0 throttle + in gear + brakes applied".

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Old 04-08-2007, 07:59 AM   #23
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Pulse and Glide while the cat is still cold would produce much more NOx and SO2, but less CO2 cause less fuel would be burned. I think the cat has to get to something like 600 deg F, before it is fully functional. I would think that in the winter (at least in VT) the cat would be doing nothing if you frequently EOC. As far as engine wear, it is hard to know...I dont know if anyone has been EOCing for over 150K. I think in warmer places, EOCing sooner after startup makes more sense.
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Old 04-08-2007, 08:28 AM   #24
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Here's what I know for sure:

Every modern EFI car utilizes a fuel enrichment map that is based upon coolant temperature, as well as one that is based upon air temperature. At what portion of the mapping the ECU operates has little to do with closed loop operation except that open loop is the designers best guess based upon all other sensor data sans the oxygen sensor - which may or may not be much less efficient. What it boils down to is that the coolant temperature enrichment map is a simple curve. The warmer the engine can safely operate, the less the temperature map will enrich the basic injector mapping. Because of this, an engine block heater will absolutely improve fuel economy - even in the summer time.

As for fuel cutoff under engine braking, it is typically rpm dependent. My bet is that this minimum limit is likely programmed using a combination of what re-engages the engine smoothly and or keeps it from outright stalling when one engages the clutch. (The momentum of the coastdown rpm should be enough to kick the motor back on instantaneously when the clutch switch is tripped.)

Anybody with a programmable ECU can play with these things for some interesting results, but it's unlikely one would gain any real economy vs. stock by doing this.
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Old 04-08-2007, 08:35 AM   #25
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The 'cold startup engine wear' is oil industry hype to get you to buy their oil. If you are running the proper oil weight for your climate, it's not an issue to be concerned with. Drainback of the oil is the primary cause of this cold start wear - which really has little to do with temperature. Once you have the motor turning that first time of the trip, the brief interludes of EOC are not going to be long enough for complete drainback of the lubrication system, so all of the important parts are already lubricated for the next bump start.
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Old 04-08-2007, 11:08 AM   #26
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Quote:
Originally Posted by Snax View Post
The 'cold startup engine wear' is oil industry hype to get you to buy their oil. If you are running the proper oil weight for your climate, it's not an issue to be concerned with. Drainback of the oil is the primary cause of this cold start wear - which really has little to do with temperature. Once you have the motor turning that first time of the trip, the brief interludes of EOC are not going to be long enough for complete drainback of the lubrication system, so all of the important parts are already lubricated for the next bump start.
I can agree to that I've seen people tear apart the engine that was in my last car after 250K miles -- the factory hatching was still visible in the cylinders :P

Quote:
My bet is that this minimum limit is likely programmed using a combination of what re-engages the engine smoothly and or keeps it from outright stalling when one engages the clutch.
When I'm in 5th -- I can feel the engine re-engage when I get down to around 1500rpm. I assume it's because there's very little gear lash in my 5th, so when the engine does come back to life, it kinda taps the driven gear :P
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Old 04-08-2007, 06:31 PM   #27
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starter

> Even if you used the starter when was the last time you replaced one.

It depends greatly on how good a starter the car had to begin with (unfortunately I've had to deal with crappy Lucas starters), and the treatment it got. Cranking when the battery is low is the worst thing you can do to a starter. Some cars or starters have circuitry that won't allow it. But if yours does allow it, and on starting you hear that super slo mo groan from the engine and possibly even a buzzing noise rather like the hum from high voltage power lines coming from the vicinity of the starter because the battery is below 10 volts, STOP! Push start, or get the battery charged, unless you like replacing starters. Starters have even exploded when subjected to that kind of abuse.

Replacing starters too many times has made me hesitant about shutting of the engine in situations where I'll have to use the starter to start up again.
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Old 04-08-2007, 06:52 PM   #28
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I use my starter dozens of times per day in my Geo and it's still working just as well as when I bought the car August 2006... actually it's really the ONLY thing that's working well. The motor mounts are starting to creak under load and theres lots of 'interesting' noises coming from virtually any moving part in the car. But whatever, @ 250K, it still moves forward/backward, steers left/right, and that's what's most important to me (that and getting 50mpg+ tanks).

I've replaced the starter in my Fiero at least twice for the 55,000kms I drove it (no hypermiling techniques at all) and even with the added stress of EOCing & FASing, 34,000kms later, I have yet to replace one in my Geo.
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Old 04-08-2007, 08:46 PM   #29
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I EOC right from the get go. I want to get to the hwy with the least amount of engine on as possible. Once at the hwy the engine can run in a more even low load state and warm on up as I ease out of town.

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Old 04-08-2007, 09:13 PM   #30
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Quote:
Originally Posted by SVOboy View Post
Engine braking = complete fuel cut.
Depends on engine speed, and coolant temperature iirc. If the car is below some rpm, it automagically "idles". This rpm depends on coolant temperature.
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