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Chip tuning

Discussion in 'The Garage' started by 88-383, Apr 30, 2006.

  1. 88-383

    88-383 1/2 ton status

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    What aribles do you have to change to speed up the idle some? My 355/cam combo makes like 50kpa/15" at cold idle. Then when it warms it drops to 30kpa/10" as the idle slows to 525RPM.

    I have everything to burn chips and can handle that part. I'm just trying to figure what params need tweaking. I tried a chip with the target idle speed vs coolant temp cranked up to 650rpm but the truck still seemed to idle down to the stock numbers. What am I missinng? I'm using Tuner CATS software.

    Kelvin
     
  2. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    Must be doing something wrong somewhere. I changed my idle vs coolant targets with tunercat and it worked fine. Can't remember having to change anything else to make it work.
     
  3. 88-383

    88-383 1/2 ton status

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    Did the changes take right away? I had the batt disconected, so that should be all I need to do right?

    Thanks

    KM
     
  4. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    You're burning an eeprom right? So you must disco the juice anyway to change proms. Yes they work right away. I'm no expert on this by any means. Just dabbling with it. There's a ton of info over on 3rdgen worth looking at. Mr Yeager seems well clued up on this stuff as do a few other members, they may well chime in in a bit.
     
  5. 88-383

    88-383 1/2 ton status

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    Actually I converted the eprom to a flash chip. But either way, the batt was disconected. I really wish this forum had a TBI tuning section!

    KM
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    I haven't messed with the idle RPM stuff, since my motor idles fine. Nor the flash stuff, just EEPROM. Actually haven't gotten any further than changing the fan temps, but it was then easy to see that my PROM's were working as the on/off temps changed. :)

    As suggested, you will probably find your answer over on thirdgen.org in the DIY-PROM section, or perhaps the plain old TPI/TBI forums over there. Either focus on searching for "radical" cam info or idle speed increase.

    This does beg the question though, is your combo so radical that vacuum *should* be that low, or do you have a vacuum leak??
     
  7. 88-383

    88-383 1/2 ton status

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    Motor idles fine ,but 525rpm is too low for my cam. The vacum falls from 15" below about 650rpm. Lingenfelter recomends 750rpm idle and the cam will give 15"s at idle.

    KM
     
  8. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    That's a lot of idle! Does he say this is a comp friendly cam?
     
  9. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    What ECM are you running? 7747?
     
  10. 88-383

    88-383 1/2 ton status

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    Yup, 7747! and this cam is very very computer and smog friendly in the TPI world. It ran so well in my TPI engines I had to give it a try. Normally you would think 650 and higher RPM is high for an engine, but it's not out of line for a performance piece.

    KM
     
  11. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    I just looked through my truck's 7747 bin, and tunerpro's ECU file, and less the desired RPM vs coolant temp table, I can't find anything that'd cause it not to increase the RPM as you set it to...
     
  12. 88-383

    88-383 1/2 ton status

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    Thanks Russ! I'll try again but with a bigger change, maybe it's doing it and I cant tell.

    KM
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    What's the original target idle? Is it truly 525RPM?

    Even that sounds low for stock to me, but I haven't (yet) logged RPM without the ECM upping the idle to 1000RPM while logging.
     
  14. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Dorian, thats probally becuase you are applying reistance between the diagnostic wire and ground. The `7747 does not require any resistance to start transmitting ALDL data, it does so all the time. If you just read the data, it shouldn't increase your RPMs at all.

    Ok, I just loaded up my 89's AMUR bin, and here is what I've found:

    At 100 degrees C, the engine should be idling at 525 RPM, according to the stock desired idle speed vs temp table. With the RPM increasing from there to 650 at 115 degrees, and decreasing from there to 600 RPM at the colder temps.

    There is a %throttle follower in the constants chart so the RPM is changed based on if you are in gear or not according to the park neutral switch. When in gear, that % is nearly 20%, and when out of gear, its approx 12%.

    Stall saver comes into effect at 400 rpm, and disengages at 525 RPM.

    Other than that, I can't find any references to idle that seems like it might affect what your idle is suppost to be. Maybe check to see what your coolant temp sensor is reading and make sure it is accurate?
     
  15. Wingnutt

    Wingnutt 1/2 ton status

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    You need to raise your IAC vs Temp counts to increase your idle speed. The IAC acts like a vacuum leak, it does NOT control the AFR like a lot of people think, but rather is used to control the idle speed. Raise the counts a bit and see what happens. Here's a short cut & past from a thread over at thirdgen.org that will help with something that you will also need to be aware of:



    Hope this helps. All of this stuff is interconnected and it helps to be able to burn a chip quickly and cheaply when troubleshooting problems....for that I HIGHLY recommend getting a Prominator. It makes downloading a new burn into a 30 second job.:D
     
  16. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Cool, good to know! I totally missed that entry the first two times I went through the ECM file!

    I'd love a prominator, but don't have nearly the cash for it :(
     
  17. 88-383

    88-383 1/2 ton status

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    Thanks guys, I was thinking that had to be it. I'll burn another chip:wink1: I still think our forum needs a TBI tuning section though! It gets old going on Thirdgen asking questions regarding how to get a K5 running better:D. But they allways seem willing to help.

    Maybe we should start a poll to check intrest? Maybe I'm all alone on this?

    Kelvin
     
  18. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    I'd love an EFI forum here! I know there are many guys running TBI, and several guys running TPI (myself included) and it'd great to be able to work together on the issues we all run into! Someone else always thinks of something that you'd never have even thought of...
     
  19. Wingnutt

    Wingnutt 1/2 ton status

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    Ditto the TBI/EFI tuning forum! Maybe Steve will open one up in the near future.:D



    Edited to add......your idle should be 650-700 rpms in C/L.
     
  20. fparker

    fparker Newbie

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    8747 or 7747

    I have a 90 Burban 2500 with a 8747, tried to program a chip, Guess I don't know enough about what is going on here. I got the 8747 file from tunercat and without any changes it runs like crap when I install it. The other chip is running the system at open loop, I guess a set of default parameters. I need to get the thing working properly, is there a place to find out the stock program and what I should change for non stock mods?
    What is the diff between the 8747 and the 7747?
    Fred
     

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