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Gas consumption in deceleration

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Old 08-05-2009, 09:13 PM   #1
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Gas consumption in deceleration

I have always wondered. I have a Taco 4.0 6 cylinder and do much offroad. My question is this... when I use the engine compression stroke to decelerate going down hill (foot off gas pedal), is there gas being fed through the injectors into the cylinders?? Is fuel still being consumed in the engine? Does the computer know when compression is being used to slow the engine and shut off the gas flow?

To me, it sure makes sense that gas flow to the injectors is shut off in deceleration, but is it???

Thanks for any help.
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Old 08-06-2009, 04:30 AM   #2
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For the first few seconds, there is still gas flow into the cylinders. Once the computer realizes the truck is coasting, it will shut off the fuel. Its very noticeable in a truck with a manual when the fuel shuts off because the truck will slow down faster but you may not even notice with an auto.
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Old 08-06-2009, 05:57 AM   #3
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Quote:
Originally Posted by sriley727 View Post
For the first few seconds, there is still gas flow into the cylinders. Once the computer realizes the truck is coasting, it will shut off the fuel. Its very noticeable in a truck with a manual when the fuel shuts off because the truck will slow down faster but you may not even notice with an auto.
Actually, its pretty noticable in the Autos also.
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Old 02-18-2010, 12:12 AM   #4
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Quote:
Originally Posted by chris4x4 View Post
Actually, its pretty noticable in the Autos also.
Is this the case with 1st gen V6 manuals, too? My 93 22RE manual never did this, but I've been noticing something strange like this in my "new" 2001. It's like a two-phase deceleration when I let off the gas, more noticeable at lower speeds. It's buggin' me, makes me wonder. I just lubed the driveline (which made soem other clunking go away), so that isn't an issue.
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Old 02-18-2010, 12:57 AM   #5
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yeah, it does as the other guys have said. my scangauge reading "9999" for gas mileage on deceleration proves it too.
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Old 02-18-2010, 09:37 AM   #6
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Quote:
Originally Posted by RelentlessTaco View Post
yeah, it does as the other guys have said. my scangauge reading "9999" for gas mileage on deceleration proves it too.
Huh. So just to be clear, I see you have a 2nd gen, and this thread started regarding a 2nd gen 4.0, but you know this to be true of the 1st gen 3.4 V6 5VZE? Did you have a scanguage in a 1st gen at some point, or see someone else's do this?

Just curious, because we are talking about different trucks and engines. I always appreciate demonstrable facts rather than hearsay or opinion on stuff like this, so I like your idea of being able to prove it with a scangauge (which obviously I don't have). This issue is kind of hard to search the threads for...

Thanks for your input.
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Old 02-18-2010, 01:00 PM   #7
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Quote:
Originally Posted by scocar View Post
Huh. So just to be clear, I see you have a 2nd gen, and this thread started regarding a 2nd gen 4.0, but you know this to be true of the 1st gen 3.4 V6 5VZE? Did you have a scanguage in a 1st gen at some point, or see someone else's do this?

Just curious, because we are talking about different trucks and engines. I always appreciate demonstrable facts rather than hearsay or opinion on stuff like this, so I like your idea of being able to prove it with a scangauge (which obviously I don't have). This issue is kind of hard to search the threads for...

Thanks for your input.
Well I was talking about a 2nd gen, but 2 guys I know have 1st gens, 1 w/ the 2.7 and one with the 3.4, that have scangauges. I try and see what theirs reads on decel next time im in their trucks.
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Old 02-18-2010, 01:18 PM   #8
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Quote:
Originally Posted by RelentlessTaco View Post
Well I was talking about a 2nd gen, but 2 guys I know have 1st gens, 1 w/ the 2.7 and one with the 3.4, that have scangauges. I try and see what theirs reads on decel next time im in their trucks.
Dood, that would be awesome. Thanks. I think half the confusion about techincal dicsussions on this site results from cross-generational vagueness and assumption. Just go check out the hubcentric lugcentric discussions....

I'm sure lots of puzzled first genners without scangauges would appreciate the info.
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