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Thread: Idle issues and lean surging on decel at highway spees

  1. #31
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    https://www.thirdgen.org/forums/diy-...crank-run.html

    here's a good thread to read. guy is using MAF code but starting tables are the same. I would try what dimented24x7 said in the last post ”if youve changed your injector flow, the crank PW table will need to be scaled to maintain the correct crank fueling.”

    so take your original injector flowrate and devide by the new flow rate: (example)
    61 / 78 = 0.78

    so now multiply that whole table by 0.78.

  2. #32
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    Thanks for all the info guys, I'm going to get the Trimalyzer set up and start fresh on this sometime this weekend hopefully.

  3. #33
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    Well so far using Trimalyzer is great I absolutely love how it's set up. It has helped a bit with my lean decel at highway speeds but I still can't seem to get the MAT/IAT sensor to influence fuel trims. I will log on my hour long drive home from work with ambient temp around 75 F and everything will be great and all trims within 5%. Then the next morning with ambient temp around 40 F, having changed nothing in the tune, I will notice lean stumbles and upon arriving at work and running the log through Trimalyzer it will be telling me to add 10-15% fuel across the board. If I add the fuel it wants I'll then find the truck running super rich in the afternoon with warmer ambient temps but it will then be ok on the next morning when it is cooler.

    It seems fairly obvious to me that for whatever reason my MAT/IAT is not influencing fueling for whatever reason. I've tried changing the MAT & CTS Blend Multiplier vs Airflow table values with no luck. I even found a thread on this forum where a guy was having the same issue and simply turned on the MAT flag and put .750 or .800 everywhere in the blend table and never had the issue again. At this point I'm thinking of retrofitting a heat pipe to my right side header to get back to the exact factory setup unless I can figure out how to get the MAT sensor working. Has anybody ran across anything like this before?

  4. #34
    Fuel Injected! ralmo94's Avatar
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    Have you reviewed to see if it reported a different temp when lean compared to when rich?
    What research I have done on the subject says tbi should use a MAT instead of an IAT, due to the fact that the fuel cools the manifold temps. Where is your sensor mounted?

    Maybe someone else has more experience.
    No need to re-invent the wheel. But we can make it better

  5. #35
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    For years I have run my BB chev in open loop. To keep it happy with oat temp changes I have used the mat sensor ticked and the blend of .852. My sensor is at the base of a non stock air cleaner so your needs might be a bit different.
    6395, BHDF, 7.4 BBC lightly modded now 6395 BMHM back to BHDF

  6. #36
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    Carb/throttle body icing is a real thing where i live . everyone always deletes the stove pipe, as if it's a performance hindrance? it helps with cold startup drivability and gets the car up to operating Temp faster..if the system is operating properly i can't see how it affects performance? I haven't tried one but also heard there are good gains from the "salad bowl" mod. my TBI caprice had an IAT "bird cage" style that was in the air cleaner. i was always told the MAT sensor (same as a CTS) was not as good because it responded to changes slower. there was actually a bird cage style one you could use from a 6.5L diesel....

  7. #37
    Fuel Injected! ralmo94's Avatar
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    Quote Originally Posted by tayto View Post
    Carb/throttle body icing is a real thing where i live . everyone always deletes the stove pipe, as if it's a performance hindrance? it helps with cold startup drivability and gets the car up to operating Temp faster..if the system is operating properly i can't see how it affects performance? I haven't tried one but also heard there are good gains from the "salad bowl" mod. my TBI caprice had an IAT "bird cage" style that was in the air cleaner. i was always told the MAT sensor (same as a CTS) was not as good because it responded to changes slower. there was actually a bird cage style one you could use from a 6.5L diesel....
    The argument about may vs iat was that as fuel is atomized it takes heat and can cool I don't imagine faster reaction time would matter that much, but I don't know.
    No need to re-invent the wheel. But we can make it better

  8. #38
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    op, i noticed you are running the edelbrock performer. i ran a vortec performer rpm which had provisions to run coolant under the carb/throttle body. vortec heads also have NO exhaust crossover. i am wondering if you are having issues until the manifold gets heat soaked? this may be a good candidate for the TBI MAF code if you are running a 4L60E or manual transmission.

    EDIT: sorry to keep rambling here, but go look at the ultra expensive GM performance TBI vortec intake. it has coolant passages running under the TBI like a stock intake....
    Attached Images Attached Images
    Last edited by tayto; 05-10-2022 at 06:21 AM.

  9. #39
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    Thanks for all the info everybody and I reall appreciate the ideas. I ran to the local pick n save near my work on lunch a couple days ago and grabbed a factory air cleaner and hose clamped a piece of pipe to the cylinder 2 header pipe and ran the flex hose from there to the air cleaner. I also had some more weirdness with the MAT sensor. When I drove home that afternoon after putting on the factory intake I realized I was still running on the chip with the MAT flag enabled and fault codes enabled and the MAT unplugged but it didn't throw any codes or affect fueling in any way which I though was odd because the MAT was reading -40 or whatever the minimum it reads is since it was unplugged.

    The really crazy thing was the next morning I installed the newest chip I burnt with the MAT flag off and MAT codes disabled and all of a sudden I was running super lean in only one area of the VE table, almost like the MAT was working but only in one area? Very weird. Anyways that's only been 2 days ago so I've really only had a chance to drive the truck once but the factory air cleaner definitely has seemed to help. I had the MAT/IAT located in pretty much the same area as the factory intake flap on the factory air cleaner (I took the whole assembly apart and installed a mounting plate I made for the temp sensor). I attached a few pics of what I did and some things I noticed in regards to the temp at TBI unit vs the rest of the engine so I can definitely see what you're saying about wanting to have it set up as a MAT instead of IAT ralmo94. I may look at where I can mount the sensor closer to the TBI unit if it's still giving me some grief. I guess I just hadn't really anticipated this big of a fit out of such a mildly built engine but I guess it's still quite a bit different from stock. Also tayto I've eyeballed that intake several times but usually right before I break down and order it my wallet slaps me in the face and says keep working with what you have lol

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    TBI unit 1 .bmp

  10. #40
    Fuel Injected! ralmo94's Avatar
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    Everything you shown looks good, but I feel it should be clarified in case not already understood, what you have is an IAT, or intake Air Temp, Not a MAT, or Manifold Air Temp. If you get the hiccups figured out it will probably work well. As stated previously ( I think someone mentioned it on this thread ) a MAT is threaded in to the intake manifold, and is the same part number as a coolant temp sensor. The difference is MAT would be able to sense temperature after fuel evaporates and atomizes, Wich lowered temp, IAT, picking temp up before the fuel has been injected can not. But if you get your IAT functional and calibrated it should work just fine for you
    No need to re-invent the wheel. But we can make it better

  11. #41
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    Oh absolutely I understand the difference, I was trying not to confuse anybody that may be looking to this thread for help by going back and forth between IAT then talking about MAT flags and MAT blend table (I actually work on cars for a living, just not tuning obviously) but I see that just added even more confusion. At this point there's really nothing else I can do as far as the IAT because I can't get it to change fueling reliably no matter what I put into the blend table or even get it to flag a code with it unplugged, unless there's another table I'm missing. The temp the ECM reads via the IAT always seems to be similar to what I would expect on any other car, slightly below ambient temp when cruising and at ambient temp or slightly higher at idle due to some heat soak so it seems like the resistance curve is acceptable and the ECM is interpreting it otherwise I would think it would be showing some erroneous value. I'm definitely no programmer or anything so if the flags and tables in the tuning program don't work I'm pretty much clueless after that unfortunately, I don't know how to go in and actually see if the changes I'm trying are actually being implemented, though if I had to guess since the addition of the sensor does nothing and no faults set with it unplugged something isn't working right somewhere. I tried updating to the newest version of tunerpro, starting with a fresh .bin file, and copying numbers off of a BPLH bin but none of that worked, that's pretty much the extent of my knowledge on this type of stuff.

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