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Thread: thoughts on rpm and speed limiters using fuel disable

  1. #1
    Fuel Injected!
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    thoughts on rpm and speed limiters using fuel disable

    I am using 1227165 ecm with $6e mask (factory) with a modified chip for an 89 firebird 305 TPI.
    I have found the parameters in TunerproRT for disable and enable fuel, for both mph and rpm.
    I am wondering if anyone has used them (say for a kid's car to limit speed, or just as a plain rev limiter for engine protection).
    what has been your experience, and are there any suggestions ?

  2. #2
    Super Moderator Six_Shooter's Avatar
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    They work.

    What are your concerns?
    The man who says something is impossible, is usually interrupted by the man doing it.

  3. #3
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    well, let's say the kid is driving it at the speed limiter say, 80 mph-- will that, if done for a long enough time, create an over lean situation that could hurt the engine?

    same thing with the rev limiter

  4. #4
    Super Moderator Six_Shooter's Avatar
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    Not if you set them right.

    There are usually two settings for each cut.

    A cut settings and a re-enable setting. Moving these two settings far enough apart, the ability to bounce repeatedly off the limiter is not only less likely, but less enjoyable.

    For example, set the speed limiter to 80 MPH so that the fuel is cut at that speed, set the re-enable at 60 MPH and the vehicle speed needs to drop below 60 MPH before the fuel will be re-enabled. Same thing for the rev limiter. I haven't looked at $6E in a while, but I'm sure it's set up this way.
    The man who says something is impossible, is usually interrupted by the man doing it.

  5. #5
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    yes, there are 2 parameters for each, disable and enable.

    I was just looking for people that have used these and what their experiences have been with them...

  6. #6
    Super Moderator Six_Shooter's Avatar
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    As I said, they work.

    I doubt you'll find anyone that tried to drive on the limiter(s) for an extended period of time, though I did in my Malibu frequently back when I was young and stupid, but only for a 10 seconds or less at a time.
    The man who says something is impossible, is usually interrupted by the man doing it.

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    think of it this way: when fuel cuts, the engine is basically in DFCO mode. spinning, but no fuel delivered(or at least none commanded, if your injectors are leaking, that's a problem).
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  8. #8
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    My 5yr old son thought it would have been funny to floor my gas pedal with my 217k mile 454 when it was it idle.

    Luckily, I set the rpm fuel cut to 4100. As it was bouncing off the rev limiter, and me running to the truck to stop him.....I learned my lesson.

    They work.

    the rev limiter from the factor is at 4800 rpm or something. I think it would have surely blown up if I hadn't dropped it. My oil pressure sucks.

  9. #9
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    Quote Originally Posted by Six_Shooter View Post
    As I said, they work.

    I doubt you'll find anyone that tried to drive on the limiter(s) for an extended period of time, though I did in my Malibu frequently back when I was young and stupid, but only for a 10 seconds or less at a time.
    On long trips in west Texas I used to set the cruise very near the speed limiter in my 97 Express it would often tag the shut off when transitioning over a hill.

    The old worn out 700r4 behind my 383 TPI in my 83 G20 would never shift 1-2 WOT without bouncing off the 6, 000 rpm limiter.
    Last edited by Fast355; 05-12-2013 at 05:08 PM.

  10. #10
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    If you have a monolithic catalyst it can be a bit rough on it - normally under DFCO conditions there's not much mass flow so the cat doesn't temperature cycle so much but with essentially atmospheric air then WOT exhaust alternating through it, well, it's not so good for it. You can crack it. I've not used pellet converters myself but they're probably immune. I'm also wondering if parts of the exhaust system doesn't like the temperature fluctuation at such a high massflow either.
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    Fuel Injected! CDeeZ's Avatar
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    I just found this thread and have wondered about this several times. In the 7427 PCM ($0D), I have my MPH to enter fuel cutoff set @ 255 MPH, and MPH to resume fueling set at 254 MPH. Basically I thought I would eliminate the MPH limiter and instead only go for a rev limiter.. I just noticed that my RPM to enter fuel cut off is 6375 RPM and RPM to resume fueling is also set at 6375 RPM. It sounds like in order to properly set this rev limiter the Resume fueling RPM should be set a little lower than the RPM to enable fuel cut off, is this correct????? Playing around with this one in TP, it looks like the next lowest setting would be 6350 RPM. So I'm thinking it should actually be set to 6375 RPM and 6350 RPM to enable fuel cutoff and resume fueling, respectively. Does this sound right to you guys?

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    Quote Originally Posted by daleulan View Post
    If you have a monolithic catalyst it can be a bit rough on it - normally under DFCO conditions there's not much mass flow so the cat doesn't temperature cycle so much but with essentially atmospheric air then WOT exhaust alternating through it, well, it's not so good for it. You can crack it. I've not used pellet converters myself but they're probably immune. I'm also wondering if parts of the exhaust system doesn't like the temperature fluctuation at such a high massflow either.
    Wondering if that is the reason for a rich blast before entering DFCO?


    Quote Originally Posted by CDeeZ View Post
    I just found this thread and have wondered about this several times. In the 7427 PCM ($0D), I have my MPH to enter fuel cutoff set @ 255 MPH, and MPH to resume fueling set at 254 MPH. Basically I thought I would eliminate the MPH limiter and instead only go for a rev limiter.. I just noticed that my RPM to enter fuel cut off is 6375 RPM and RPM to resume fueling is also set at 6375 RPM. It sounds like in order to properly set this rev limiter the Resume fueling RPM should be set a little lower than the RPM to enable fuel cut off, is this correct????? Playing around with this one in TP, it looks like the next lowest setting would be 6350 RPM. So I'm thinking it should actually be set to 6375 RPM and 6350 RPM to enable fuel cutoff and resume fueling, respectively. Does this sound right to you guys?
    Yup! But that close in RPM it seems to hit rev fuel cutoff and just go lean... if you spread it out to 100 RPM well then it actually cuts in and out.

    I've not done this as fact but is each one seperate? Or do both have to qualify? RPM alone did work in $0E when I did one without a VSS.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
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  13. #13
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    Quote Originally Posted by CDeeZ View Post
    I just found this thread and have wondered about this several times. In the 7427 PCM ($0D), I have my MPH to enter fuel cutoff set @ 255 MPH, and MPH to resume fueling set at 254 MPH. Basically I thought I would eliminate the MPH limiter and instead only go for a rev limiter.. I just noticed that my RPM to enter fuel cut off is 6375 RPM and RPM to resume fueling is also set at 6375 RPM. It sounds like in order to properly set this rev limiter the Resume fueling RPM should be set a little lower than the RPM to enable fuel cut off, is this correct????? Playing around with this one in TP, it looks like the next lowest setting would be 6350 RPM. So I'm thinking it should actually be set to 6375 RPM and 6350 RPM to enable fuel cutoff and resume fueling, respectively. Does this sound right to you guys?
    if I remember correctly, this is close to what my stock bin was set, just a few rpm below the cut-off, but (LOL) it was at something like 10,500....
    on the most recent bin I programmed, I set it to 750 rpm difference, haven't yet tried it though.

  14. #14
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    there does need to be a bit of a hysteresis for on/off, otherwise you'll run into a "floating" condition, doesn't quite feel like a rev limiter.
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  15. #15
    Fuel Injected! CDeeZ's Avatar
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    Hysteresis, there's that word again! So basically the parameters need a little space in between.... Just like when I was tinkering with my Efan ON/OFF settings, I remember I originally had set the parameters too tight, or with not enough 'hysteresis' for the fan to cycle on and off properly..

    Bada bing!

    750 RPM difference? Do you think that is a little much?

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