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Old 11-17-2008, 09:55 PM   #11 (permalink)
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Unless the engine is physically turning, the tranny pump isn't pumping...

I would rather have a warm fuzzy by just neutral coasting an automatic, engine on. I would think engine off coasting in gear with an automatic would cause compression braking, and wear and tear on the restarts, etc. Not for me, sorry. Good luck on that. Way too much work and way too much risk.

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Old 11-17-2008, 10:13 PM   #12 (permalink)
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Ok, first of all, the whole point of this is that I'm using compression braking anyway on the steep hills and stop-n-go traffic around town, so I want to cut the injectors while doing that. The car does have a fuel cut mode, but it is uber suck- I tested it today, the injectors run even when the brakes are applied.
Sorry if I sound condescending, I appreciate everyones input here and I'm just trying to get my objectives across.

99Metro- Do you mean the engine needs to be running, or simply turning?
I ask because with the EOC method I'm using, the engine is turning. I think the tranny pump is pumping whenever the crankshaft is turning. But, heh, I've been wrong before...
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Old 11-17-2008, 10:48 PM   #13 (permalink)
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If the whole driveline is turning, unless you have an electric fuel pump, then yes, the tranny's pump is turning, thus, pumping.

One thing that anyone with an automatic tranny can do is to go to a dealer w/ the VIN of your car, and find out if it was equipped with a "tow-behind" package. If it was, you can coast, engine off, in neutral, and not damage anything.

The odds of this are highly unlikely, but you may be lucky.

Other than that, yes, if the crankshaft is turning, as a general rule, so is the tranny pump.

BTW, If you have a dead battery, coasting at 25 mph will start your engine in an automatic car... just like pop-starting a manual. (Except certain models, as is the case with all automatic "quirks")
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Old 11-17-2008, 11:14 PM   #14 (permalink)
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Awesome,
I know I don't have a tow-behind package (she was a Hertz fleet car).
I'll just be using EOC during compression braking anyway, so everything works out!
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Old 11-17-2008, 11:23 PM   #15 (permalink)
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Just remember that you don't need to hit neutral or use the starter to restart the engine... all you have to do is complete the circuit again (turn the key to "On" again).

The engine spinning without actually running will not affect it one iota... the oil pump is mechanically driven by the rotating assembly, therefore, it will still pump oil through the engine, and nothing will be harmed... in fact, in new engines, this actually helps to seat the rings, since vacuum in the engine block pulls the rings outward to the cylinder walls.

If you feel that you're slowing down too much w/ the engine off, push the gas pedal to lessen the vacuum on the engine, thus reducing compression braking. This will NOT flood a fuel injected engine.

Also, remember not to push the accelerator immediately after restarting the engine. The fuel pump will still be in "prime mode" and may flood the engine if you open the throttle.
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Old 11-17-2008, 11:31 PM   #16 (permalink)
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Quote:
Originally Posted by Oval_Overload View Post
Ok, first of all, the whole point of this is that I'm using compression braking anyway on the steep hills and stop-n-go traffic around town, so I want to cut the injectors while doing that. The car does have a fuel cut mode, but it is uber suck- I tested it today, the injectors run even when the brakes are applied.
Sorry if I sound condescending, I appreciate everyones input here and I'm just trying to get my objectives across.

99Metro- Do you mean the engine needs to be running, or simply turning?
I ask because with the EOC method I'm using, the engine is turning. I think the tranny pump is pumping whenever the crankshaft is turning. But, heh, I've been wrong before...
I understand your cost-benefit ratio with using EOC -- I do the same with my automatic, but in Neutral. I've been told that fluid pressure for the lubrication system is absent and puts undue strain on clutch packs and other internals when forced to turn (especially at high speeds) while engaged.

I consulted the shop manual for my vehicle. In this instance, the main shaft should turn and provide pressure for the ATF pump. But, the Regulator Valve determines how much fluid is pumped and where. Here's the basic schematic for its operation...

General Hydraulic Pressure:

ATF Pump -> Regulator Valve into 3 outputs ->

-> Line Pressure (shifting action)
-> Torque Converter Pressure (engagement hydraulic coupling)
-> Lubrication Pressure (Where we want to focus)

The TC's stator rotates via torque from the crankshaft. In conditions of torque (engine running, acceleration), turns a shaft, moves the spring-loaded arm on the fluid pressure regulator and feeds the system with ATF.

As I understand it, torque converter pressure remains when the engine is cut because the regulator valve receives no torque and closes. Now, fluid cannot be pumped into the lubrication system. Clutch packs turn with the absence of sufficient fluid, and can be susceptible to accelerate heat and wear.

It's a complex operation -- if I'm incorrect in how I interpreted this system, then let me know

As always, every transmission model is different, your mileage may vary...

-Rick
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Old 11-17-2008, 11:34 PM   #17 (permalink)
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Christ...
If I could mail someone a hug, you would get one! lol
Everything you stated is exactly what I suspected.
However, I did not know about opening the throttle to lessen the compression. Awesome tip! Thank you all very much!
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Old 11-17-2008, 11:44 PM   #18 (permalink)
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RH77 - you're exactly correct, except one thing. When you're coasting and the engine is turning, w/ the throttle off, it doesn't do damage to the transmission, other than normal wear. By turning off the engine, and leaving the transmission in gear, you've effectively done nothing but stop the fuel consumption...

Engine is still turning, although not providing torque, transmission is still engaged, and therefore, pump is still working. One could confirm this by installing a pressure gauge inline w/ the tranny cooler. (Just a thought)

Also, a trans temp gauge might be beneficial.

If you doubt that this will not harm a transmission (anyone), you should also consider that in an automatic, the most effective means of slowing down and maintaining speed is STILL downshifting.

The torque convertor and clutch packs will not engage fully until engine RPM is speed matched to the vehicle speed per the gear, therefore, it's just as "damaging" as it would be to your clutch while doing so in a manual.

Oval Overlord - Hug accepted (even if you're a dude... I'm comfortable) Although I will tell you that you should not just take my word for it. Ask a "professional"... and not just one. Never just take one person's word for ANYTHING without verifying it, especially when that person is a screenname on a website or forum. Google is still your friend.
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Old 11-17-2008, 11:54 PM   #19 (permalink)
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I shall ask the dealer mechanic!
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Old 11-17-2008, 11:57 PM   #20 (permalink)
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That's the spirit! Hell, take him a print out of this thread, and ask if it's correct...

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