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Thread: 7427 upgrade tuning help understanding

  1. #46
    Super Moderator dave w's Avatar
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    Quote Originally Posted by typhoonss92 View Post
    besides the injector flow being changed when you up the psi or put in bigger injectors is there any other perameters or tables that need to be changed
    The Injector Offset Tables are parameters that are important for tuning.

    The screen shot below shows injector offset tables from 94 Pickup with a 4.3 $OD and a 94 Pickup with a 7.4 $OE. There is "Internet" information the 94 7.4 (28 PSI) uses the same injectors as the 94 4.3 (13 PSI). If the "Internet" is correct, then the fuel pressure difference between the 13 PSI 4.3 injector vs. the 28 PSI 7.4 injector would account for the differences in the injector offset tables?

    dave w
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  2. #47
    Fuel Injected!
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    Something doesn't sound right, I don't think you should be maxing out your VE table just off idle and then requiring less VE under higher load/RPM.

    If I was setting up for a larger sized injector or different fuel pressure I'd nominate a value that I'd want as max DC% under W.O.T and max RPM, say 85% and then carefully test run to make sure the Wideband AFR at 95-100 Kpa/max RPM were around 12.2- 12.5 range.
    That establishes a baseline for max fuel requirement, once I had the VE adjusted to achieve that AFR (VE's in that range around the mid 90's rather than 100%) I'd then work back tuning the rest of the table from there.
    That's just how I'd look at doing it anyway.

  3. #48
    Fuel Injected!
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    ok so I mostly have this tune figured out, 2 things I really need to figure out though.
    1- the speed is off by 3-5mph, so when I take off it is 0 till I hit 3-5 mph, is there any way to change this(parameter)
    2- I have a surge at idle only in park without the a/c on, with a/c on no surge. I have tried adding 2+/- degrees from the 600-800rpm up to 60 map. it surges on the wbo2 from 14 low surge up to 18 or 19 high surge. the very end of this datalog shows the surge I pulled in the driveway and idled in drive for about 15 sec then put it in park for about 15-20 sec. Not sure what else to try

    I have most of the fueling issue resolved, figure out how to get my fuel psi up to 24 so VE is not maxing out now.
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    Last edited by typhoonss92; 06-20-2019 at 06:13 PM.

  4. #49
    Fuel Injected!
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    So I made a few changed, proportional gains unstable and stable and lowered. I also took out the under and over idle rpm and made it zero's. Drove the truck, still see a slight surge at .7v tps at about 30-35 when I am steady but the rest is almost there. I got home and idled in drive for 20 sec good then into park it was fine for about 8-10 sec where it was 12.3 on the wbo2 then shot up to 14.6 and started surging. I shut the motor off and then restarted and adjusted idle screw in openloop so there was 9-10 iac, shut off truck for 10 sec to reset tps and started back up. open look was steady idle went into closed loop was good for 8-10 sec again surged like before. I set both idle and minimum blm to 128 because at 14.7 wideband blm shows min of 105 so it kept taking out fuel. The only time the blm would raise is when the afr dropped to 12.2-3 blm would be 122-126. So for testing I just set it to 128, seems I was chasing my tail adding fuel and computer was taking it away.
    Since I set the blm to 128 is the computer reading the nbo2 and adjusting for that? I ran my 7747 in openloop and had the truck dialed in pretty good, maybe I should just do that to this computer would help not having the computer adj for epa or maybe ther is just a parameter I don't understand what it does so I don't know to change it.

  5. #50
    Fuel Injected!
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    I have tried a few things, played with air% at idle, o2 sensor rich/lean, and a few other idle settings but still get this surge, something changes while it is idling. when I put it in park it is at 12.2 to 12.4 wbo2 then after a few seconds probably 5 sec the wbo2 goes to 14ish and then starts to surge from high 13 to sometimes past 20 where it says lean, I have seen the AE kick on and have seen stall saver kick on at times. I decided to go back and start the tune over since I have made so many changes and maybe something is just off, I copied over SA, VE, AE, PE settings and injector flow and cylinder volume, turned off the egr, cpp, mph and rpm limiters and set wbo2. The only mechanical thing changed was the idle screw but that got me a little more iac at idle when warmed up so I had about 10. I'll take it out in a little bit and see how it runs.

    I would still like to know if there is something to adj the speed/mph it is about 5mph slow

  6. #51
    Fuel Injected!
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    alright tested and with no modification to the o2 or idle except 800rpm drive and 900rpm park, it still does it in park after warmed up. Acts a little different though. put in park idles at wbo2 12.3 for about 5 sec then slowly raises up to around 14 so maybe another 5 sec then very lightly surges for about 3-4 sec then big surge that does not stop.
    So there is something when you go to park that has a delay of a few seconds to make it rich then lean out. The blm is set at 128 min in idle to troubleshoot this or maybe I am looking at this wrong and it is too much air?

    Any Thoughts, I have all day tomorrow to mess with this

  7. #52
    Electronic Ignition!
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    There is a separate idle BLM value for drive and park and also with the A/C on or off. What is your timing look like when the idle surges? Could your closed throttle MAP vs RPM timing table be causing the problem? For example, the BLM comes down to target stoich, vacuum increases causing you to be in a cell with more advanced timing, engine revs up, putting in a cell with less timing, causing the engine speed to then drop? Also is your idle VE table reasonably well tuned? As the engine surges you could be swinging between cells that are significantly richer or leaner and adding to the problem. You can raise your Maximum MPH for Idle VE and Maximum TPS for Idle VE to allow you to stay in the idle VE table so that you can tune it

  8. #53
    Fuel Injected!
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    Both the open and closed SA are 26 degrees from low map to 60map up to the 1000 rpm mark, then the 65 map is 25 degrees. Both Idle and regular BLM are set to 128 minimum right now. here is idle VE and closed throttle SA. VE tables are tuned to wbo2 pretty close. This only happens in park with the ac off.
    It seems after 7-10 sec something is ramping up the iac causing a lean condition.
    idle in park when it is steady at the beginning is high 30's to low 40's kpa then when it surges goes from mid 30's to mid 50's and the rpm will go as low as 500 and as high as 1175rpm
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  9. #54
    Electronic Ignition!
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    Your Idle VE table looks very lumpy. When you look at the table graph, your values should have a nice smooth transition without large peaks or valleys.

    Remember that the computer is interpolating between 4 adjacent cells at any given time to do it's calculations. For example, at 700 RPM at 40ish MAP, your computer is calculating using an interpolated value based on the 600 and 800 RPM rows in the 40 column and also the 35 or 50 column depending on which side of 40 MAP that it's reading at that instant.

    Your values in the 40 column for 600 and 800 are 50.4 and 44.9. The idle speed is always changing slightly, even as normal operation, and the computer will continually try to self correct. As the idle speed drops, it's interpolating the values from the table and reading that VE is rising, therefore making the engine run richer, causing vacuum to drop, shifting towards a higher load cell with a higher VE value, causing the engine to run even richer as the IAC opens to prevent a stall, it overshoots and sends you near the 50 MAP 1200 RPM cell where the engine leans out and trys to stabilize, but fails to and the cycle repeats. That is what I suspect is happening.

    I suggest raising your Maximum MPH for Idle VE and Maximum TPS for Idle VE temporarily to allow you to stay in the idle VE table at various speeds and loads and spend some time dialing this in. Whether you tune with your wideband or unlocking and using BLMs, be sure to smooth out your table and do a quick sanity check to make sure the values are moving in the right direction. For the most part, higher MAP, or higher RPM will result in higher VE, especially with your idle map that maxes out at 1800 RPM, you're not going to be hitting any airflow restrictions that would significantly skew your VE.

    Attached is my Idle VE table. It's not perfect, but its in the ballpark and is a lot closer than the factory table was. Block Learn will take care of the rest. Notice the trend from low MAP, low RPM, low VE to high MAP, high RPM, high VE and smooth transitions. You can disregard the fact that the 100 column dips down and it really shouldn't, but thats how it was from GM and I didn't bother with it because realistically, it'll be running on the Open throttle table before I get anywhere near that column. I suspect that was the engineer's thought as well.
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  10. #55
    Fuel Injected!
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    Ty, very detailed response, completely understand. I have just been using the excel sheet Dave made for the wbo2 and copy and paste. I think I remember a few years ago dave saying to smooth out the table after running the excel sheet. It completely makes sense. I tried this and now it seems I am just rich so I will play around with it but rump rump rump went away.

    There has to be a parameter for initial startup AFR or something, it goes to 10.2 maybe 10.3 for a little bit then slowly up into the mid 11's. If i push the gas at all motor dies for a split second then ramps up, this happens for about 4-5 minutes till around say 100-110 deg f then it is at mid 11 to 12 on wideband. So there must be something for initial AFR and it is called something else. such a difference from the 7747 to 7427, so much more to learn. Thanks for your time and knowledge.

  11. #56
    Electronic Ignition!
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    Make sure your stoichiometric afr is set correctly for your fuel. Any change here will affect your ve tables. Your computer will calculate fueling using this value and your ve tables, then make adjustments using other tables such as Open Loop AFR vs Temperature vs Vacuum, PE AFR vs Temperature, etc. Everything working correctly depends on having your VE tables correct.

  12. #57
    Fuel Injected!
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    I made 2 test hits today and it is getting better just the original start so I will have to wait till tomorrow for that again. But that is what I am looking for, for the parameters. I normally just go out to my back roads and do WOT and cruise but usually only get up to 65-70mph. The highway sucks most of the time so I know certain times to go get that and my granny driving done at the same time. I was able to hit the hiway on the second test today.
    Is there a way in the 7427 computer to set something like the 7747 hiway? Something where I don't change the VE tables but when it cruises after so many sec it lowers VE or raises afr. Hiway is right around 14.5 +/- .4 at 75-85mph. I mostly cruise at 80mph rarely over that. You have been so helpful with this info. I am getting very close to where I want to be.

  13. #58
    Electronic Ignition!
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    http://www.gearhead-efi.com/Fuel-Inj...OD-Lean-Cruise

    Check out post 14. It seems the pcm has similar functionality built in. I have not played with this yet. Good luck.

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