VX injector cutoff? - Fuelly Forums

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Old 09-08-2008, 11:22 AM   #1
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VX injector cutoff?

I've tried searching the threads for this and have only found 2nd hand answers...

--> Can anyone *definitively* tell me whether my '95 Civic VX (stock) turns off the fuel injectors during coasting while in gear and throttle off (engine on)?


I don't drive much so it takes a fair while to go through a tank and have been getting some whacky FE #'s after trying some new driving techniques and minor aero mods (front air dam and LLR tires)

I was getting in the mid-upper 40's prior to new driving habits. (based on 4 tanks of gas and filling it till I'd get a tiny bit of spillover out the fillertube -for consistency in measuring FE)

Not that I should complain about this but I got one tank that gave me 64mpg! The others, 39 mpg (very hilly w/passenger)and the latest is 56 mpg - First and last based on 2/3t tank, middle one on about 3/8 fillup.

I just can't accept (tho am happy to) such a dramatic increase in FE from a little bit of drafting and coasting and am second guessing the accuracy of how I fill the tank.

So I just wanted to get my head around what the car is actually doing during certain procedures to better evaluate the results.

Thanks!
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Old 09-08-2008, 01:30 PM   #2
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According to the factory service manual, page 11-29: "During deceleration with the throttle valve closed, current to the injectors is cut off to improve fuel economy at speeds over following rpm:... D15Z1 engine 850 rpm". Although this is out of a 1992 manual, I have a P07 from a later (94 I think) VX and have observed that behavior once the engine is warm. It doesn't cut off when the engine is cold. Is that definitive enough for ya?
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Old 09-08-2008, 01:37 PM   #3
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Quote:
Originally Posted by nowhhs View Post
According to the factory service manual, page 11-29: "During deceleration with the throttle valve closed, current to the injectors is cut off to improve fuel economy at speeds over following rpm:... D15Z1 engine 850 rpm". Although this is out of a 1992 manual, I have a P07 from a later (94 I think) VX and have observed that behavior once the engine is warm. It doesn't cut off when the engine is cold. Is that definitive enough for ya?
Cool, I was curious as to what rpm it had to be above, thanks for the info!
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Old 09-08-2008, 04:15 PM   #4
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Quote:
Originally Posted by nowhhs View Post
According to the factory service manual, page 11-29: "During deceleration with the throttle valve closed, current to the injectors is cut off to improve fuel economy at speeds over following rpm:... D15Z1 engine 850 rpm". Although this is out of a 1992 manual, I have a P07 from a later (94 I think) VX and have observed that behavior once the engine is warm. It doesn't cut off when the engine is cold. Is that definitive enough for ya?
Why yes, yes it is.

Thanks!
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Old 09-08-2008, 04:49 PM   #5
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My experience in my truck is that it won't DFCO while running in open loop. The engine has to be warm enough to switch to closed loop to DFCO.

-Jay
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Old 09-08-2008, 07:30 PM   #6
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We're talking about a civic vx, not a chevy truck. (Not being disparaging, I have a 72 Blazer myself, but its not the same thing). With its wideband O2 sensor, the vx is pretty much always in closed loop.
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Old 09-08-2008, 07:31 PM   #7
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Oh, and glad I could contribute.
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Old 09-08-2008, 07:45 PM   #8
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My average mileage is dropping because I replaced the original tires (made in March 1993) with some new Michelins. My car has less than 40 K miles, bought in March 08 salvage, wrecked when 2 years old with 27,492 miles.

Best tank for me was 68.5 with extreme conservative driving.

Fuel injector shutoff depends on accessory loads applied. With no loads, at lowest idle speeds it will work down to 860 RPM. With the AC on it will work down to about 1300 RPM.

Its pretty easy to feel it if you let it slow down in gear. Once you loose fuel shutoff you will feel the car stop decelerating and it will either move along at a constant speed or slightly accelerate.

regards
gary
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Old 09-08-2008, 07:48 PM   #9
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Quote:
We're talking about a civic vx, not a chevy truck. (Not being disparaging, I have a 72 Blazer myself, but its not the same thing). With its wideband O2 sensor, the vx is pretty much always in closed loop.
I understand that, but it makes sense that it won't DFCO until its warmed up.

-Jay
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Old 09-09-2008, 05:09 AM   #10
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Quote:
Originally Posted by R.I.D.E. View Post
My average mileage is dropping because I replaced the original tires (made in March 1993) with some new Michelins. My car has less than 40 K miles, bought in March 08 salvage, wrecked when 2 years old with 27,492 miles.

Best tank for me was 68.5 with extreme conservative driving.

Fuel injector shutoff depends on accessory loads applied. With no loads, at lowest idle speeds it will work down to 860 RPM. With the AC on it will work down to about 1300 RPM.

Its pretty easy to feel it if you let it slow down in gear. Once you loose fuel shutoff you will feel the car stop decelerating and it will either move along at a constant speed or slightly accelerate.

regards
gary
Good info, good thread.
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