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Thread: Tuning help needed - '91 TBI 383 w/ Vortec heads

  1. #46
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    Quote Originally Posted by donf View Post
    Sounds like a good plan. I use to work in front of a machine shop. I had to do their R&R's sometimes when things went wrong. The big thing that got them over and over was hone grit. They would get in a hurry and just hone it with what ever they thought was standard. Different brands and ring types will tell you what grit to hone the cylinders. As far as beating on it, vs not I really don't think that makes the difference compared to having a machinist who reads and follows the ring manufactures instructions. Some cylinder pressure behind the rings though will push them out against the walls harder. I do think if your rings have not fully seated, switching to conventional oil may help. It doesn't even have to be the good stuff if you do not have a flat tappet cam. If it does, one with zinc will help.
    What he said to seat rings...wind it up and let the compression slow the vehicle down repeat like a dozen or so times.
    Last edited by stew86MCSS396; 5 Days Ago at 07:41 PM.

  2. #47
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    Quote Originally Posted by stew86MCSS396 View Post
    What he said to seat rings...wind it up and let the compression slow the vehicle down repeat like a dozen or so times.
    Switched to Rotella T4 (conventional) over the weekend. We'll see what happens. Back to tuning.

    I like the idea of winding it up and using compression to slow it down to seat the rings but there's a problem......that's where I have my worst tuning problems. After oil change I took it on a home depot run and it ran great until I came off the freeway on a downhill ramp. I dropped it down twice, when I hit second it went up to about 3000 and I started getting some popping/light backfiring out the tailpipe. And it seems like after that event happens, my idle gets messed up. 100-200 higher than commanded and some hunting with a range of about +/- 75 rpm. Then after an engine stop and restart, it seems to be back to normal, idling at commanded speed and no hunting. I have only seen that behavior a few times though so I don't know if it's consistent.

    I've been shopping for a WB kit. Suggestions? I'll probably just go with a typical AEM kit with gauge and sensor. How does logging work with a kit like this? Sorry for the dumb questions, but does data go through my ECM (extra channels?) or does it go directly to my laptop/tuner pro and then logged simultaneously? I've read some threads on the former method and it seems like that may be out of my league. Or maybe I should forego simultaneous logging altogether to keep it simple? Again, if it sounds like I don't have a clue what I'm doing, it's because I don't! Is there a WB tuning for dummies thread that someone could point me to?

  3. #48
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    Popping out the tail pipe is rich, not unusual, I had to take some fuel out there too but I only have 19.5 psi. I think it will be especially bad if you have the fuel pressure jacked way up to almost 30 lbs. That is why I don't like to run any higher fuel pressure than really necessary as there is a trade off sometimes in transitions not being as clean. Hopefully you can work it out by adjusting the VE table more. I like the AEM X-series that has some improvements over the older version you linked to. I use the wide band sensor in that series, you have to redo the math, but its fairly easy.

  4. #49
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    Quote Originally Posted by donf View Post
    Popping out the tail pipe is rich, not unusual, I had to take some fuel out there too but I only have 19.5 psi. I think it will be especially bad if you have the fuel pressure jacked way up to almost 30 lbs. That is why I don't like to run any higher fuel pressure than really necessary as there is a trade off sometimes in transitions not being as clean. Hopefully you can work it out by adjusting the VE table more. I like the AEM X-series that has some improvements over the older version you linked to. I use the wide band sensor in that series, you have to redo the math, but its fairly easy.
    Thanks. My fuel pressure is only 13 psi, so that shouldn’t be the problem. I think my surging, popping, and general bad behavior during decel are timing or O2 sensor related. I’ve been noticing O2 output readings drop to near zero (low double digits) every time it surges.

    I’ll take a look at the AEM X-series, thanks.

  5. #50
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    So I tried an experiment today. Burned a new chip that had closed loop tuned out - wouldn’t come on till 150 deg. C. Runs great, all decel surging problems are eliminated by running in open loop only. Of course I know I can’t keep it like that, but at least I know for sure that this is a closed-loop problem. Now just to figure out what it is.

  6. #51
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    Just a thought, have you tried DFCO (Decel Fuel Cut-Off)? My 88 (7747) came with it, good for engine braking too.

  7. #52
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    Quote Originally Posted by PlayingWithTBI View Post
    Just a thought, have you tried DFCO (Decel Fuel Cut-Off)? My 88 (7747) came with it, good for engine braking too.
    Hmmm, interesting thought - I was considering DFCO as possibly part of the problem and actually tuned it out at one point (didn’t help) but I haven’t considering it as the solution. So right now my .bin is set up thus for DFCO:

    Scalars:
    DFCO Exit Fuel BPW Adder: 1.95 mSec
    DFCO Delay Time: 4 sec
    DFCO Max TPS: 1.56%
    DFCO BPW Multiplier Step: 0.37 Mult by

    Tables:
    DFCO RPM Limits: HI 1650 / LO 1350 RPM
    DFCO MPH Limits: HI 25 / LO 20 MPH
    DFCO MAP Limits: HI 15.88 / LO 28.06

    Suggestions on adjusting things to make DFCO more functional/used more often? It seems like such a narrow band of parameters where it actually gets used.

    Would there be any way to just make decel switch to/stay in Open Loop?

  8. #53
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    Here's where mine were set, HTH
    Attached Images Attached Images

  9. #54
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    Quote Originally Posted by PlayingWithTBI View Post
    Here's where mine were set, HTH
    Thanks much, that is helpful. I'll try playing around with them.

  10. #55
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    My 8625 PCM using OD has some similar and some different DFCO values, yours make more sense to me.

    I have AFR surging during deceleration but it's not overly noticeable in the vehicle. Your experiment with trying open loop made me think about looking at an old log I took with closed loop off. Sure enough there are no large AFR swings when decelerating in open loop compared to the large swings when in closed loop.
    It will be interesting to see what you find to be the cause, I suspect it will help solve my issue as well.
    Attached Images Attached Images

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