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Injectors while coasting or in gear

Discussion in 'Technical Chat' started by Evil Monkey, Oct 30, 2010.

  1. Oct 30, 2010 at 8:30 PM
    #1
    Evil Monkey

    Evil Monkey [OP] There's an evil monkey in my truck

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    So, I've read about how some say the injectors shut off when coasting in gear whereas in neutral they don't so the best way to save fuel is to coast in gear (drive).

    I found out my Aeroforce gauge has the ability to read the injector pulse width in milliseconds so I set it up to monitor the Inj PW setting. Here's what I found:

    While in neutral and coasting, the injector pulsewidth is about 2.0-2.1 msec. While coasting in gear it's 1.9-2.0 ms. The difference is only about 100 microseconds. So that would indicate to me that they do not shut off while in gear and coasting. I noticed a difference in my gauge to what the scangauge users were saying happens when they coast. On mine, I get higher mpgs coasting in neutral than I do in gear. While it uses slightly less fuel in gear, the transmission slows the vehicle which results in a lower mpg. When first putting the transmission into neutral, the pulsewidth jumps up to about 2.6 msec (rpm rise that others complain about). Shortly after than it drops down to the 2.0 msec setting.

    For reference cruising down the highway can range anywhere from 4.0-7.0msec and hard acceleration can go up to 15 msec. I believe that the measurement is for a 20msec time period, that is for every 20 msecs, the injectors are on for 2msec during coasting.

    Perhaps someone with an automatic and an Aeroforce gauge can monitor their Inj PW setting and see what happens.
     
  2. Oct 30, 2010 at 8:36 PM
    #2
    topgun155

    topgun155 Well-Known Member

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    The only thing I can think of is that while they might be pulsing maybe there isn't much fuel flowing.
    My scan guage is normally within .1 maybe .2 of a gallon at fillup.
     
  3. Oct 30, 2010 at 8:42 PM
    #3
    Evil Monkey

    Evil Monkey [OP] There's an evil monkey in my truck

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    I read somewhere where some guy said the scangauge gets it's setting for determining mpg base on airflow (I think it was on ecomodder). So it might make sense that if the throttle was closed that it might assume no gas was flowing.
     
  4. Oct 30, 2010 at 8:48 PM
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    My68ur8trd

    My68ur8trd Well-Known Member Vendor

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    If you have a wideband it will show you exactly what's going. The reading goes to oxygen when it goes into fuel cut. Which indicates the injectors are shut down.

    Interesting find with the aero gauge

    Justin
     
  5. Oct 31, 2010 at 7:17 AM
    #5
    Evil Monkey

    Evil Monkey [OP] There's an evil monkey in my truck

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    Yeah there isn't much fuel flowing but it seems to be about the same in gear as it is in neutral. I believe the scan period is every 20 msecs. So out of 20 msecs, the injectors are pumping for 2 msecs while in coasting in gear or while coasting in neutral.

    I'm just wondering if the automatic has some feature in it that tells the computer to shut off the fuel completely (0msec).
     
  6. Oct 31, 2010 at 7:46 AM
    #6
    buddywh1

    buddywh1 Well-Known Member

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    They can't cut off completely so it makes sense to me. The reason is the catalytic converters need exhaust gasses to stay at proper operating temperature, which is pretty hot.

    Whether it's more economical at idle while coasting, or left in gear and let the computer cut the mix way back may be a topic of some debate, but to me it's moot 'cause I'd much rather use engine braking to avoid wear and tear on brakes and auto tranny as I shift in and out to coast.

    My opinion is you'd never measure the gas mileage difference...it will be swamped by other far more influential variables. But then, if you're a hyper-miler then I guess you're trying to control all the variables for maximum benefit!
     
  7. Oct 31, 2010 at 7:54 AM
    #7
    Evil Monkey

    Evil Monkey [OP] There's an evil monkey in my truck

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    Yeah, I was thinking about coasting down a long grade. Because of the higher gearing of the manual, it tends to slow the vehicle down when coasting in gear. I usually engine brake.
     
  8. Mar 25, 2011 at 12:13 PM
    #8
    epa4wd

    epa4wd Well-Known Member

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    This is a bit of an old thread but wanted to let you know that in my 09 with 4 speed A/T, when coasting in Drive PW shows 1.9ms, in neutral it goes to 2.5ms, also when coasting in Drive Transmission temperature goes up 3-5 degrees.
     
  9. Mar 25, 2011 at 1:27 PM
    #9
    macgyver

    macgyver Well-Known Member

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    This ^^

    I had a wideband in my old accord when it was turbo'ed. When I de-cellerated in gear, my wideband readout would read "LEAN" when I would coast in nuetral, the readout would read around 14.7 (Stoich)
     
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