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Thread: Boost issue

  1. #1

    Boost issue

    I'm trying to diagnose a boost issue. My truck will not go above 23lbs of boost. I'm trying to decide if its tuneing issue or hard parts? I started datalogging the "turbo wastegate Dc" and it sits @ 69.9% whether I'm idling or hammering up a hill. I was partially expecting that number to bounce in-between 70-100. I do have my waste min duty cycle set to 70 in my tune and max at 100.
    Also while back my boost solinoid died and I replaced with an aftermarket one, which I'm wondering if thats the issue? I have also noticed in my older datalogs I never had anything beyond 23 as well?
    I will post a log little later
    Last edited by bradshaw106; 11-02-2020 at 09:00 AM.

  2. #2
    I have been doing some forum searches since i got home from datalogging. One thing i have found is refrence to adjusting estimated airflow tables. What is strange is not everyone does that? considering how little its mentioned im thinking most people dont do it. i will attach a log, you can clearly see the boost hitting 23 and flatting off. any ideas
    ATTACH=CONFIG]104618[/ATTACH]
    Attached Files Attached Files
    05 qclb nv5600
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  3. #3
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    Airflow tables are like a direct feed to your wastegate solenoid to get a desired airflow. Those not running a factory turbo can ignore those tables.

  4. #4
    Do you know what else these tables effect? I have found a calculation, so I can set it so my turbo won't go above 35psi theoretically. But will it throw anything else off?

  5. #5
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    Those airflow tables define your desired airflow, thus controls wastegate position, it doesn?t do anything with other tables. As said above, those not running a stock turbo can ignore those airflow tables. Those airflow tables are meaningless once not running a stock turbo. So not sure what you mean by what other tables it will affect. You change airflow of course it will change how the engine runs just like changing timing or rail pressure will change how an engine will run. Advancing timing can cause the effect of lowering airflow.
    Last edited by Jim P; 11-02-2020 at 01:38 PM.

  6. #6
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    Just because a person can run 35psi of boost doesn?t mean you should either. It?s not necessarily true that more boost equals more power. There is a point where boost can hurt performance and you?d find better gains from lowering boost and adding in more timing. Rather than being concerned over boost, airflow should be matched with fuel flow is the more logical approach.

  7. #7
    my thought is this map is used by the ecu for a target airflow. which the ecu use absolute pressure to bring the airflow(based on a calculation) to the target on the map. because the calculation is based off of things that cannot be changed by the ecu i.e IAT, engine volume,rpm. it will adjust the turbo wastegate to manipulate the absolute pressure, which is another varible in the calulation.
    05 qclb nv5600
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  8. #8
    i definlty understand more boost isnt always the answer, 35lbs was just a random number i pulled out of thing air. their comes a point when your outside of your turbos map and its just blowing hot air.
    05 qclb nv5600
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  9. #9
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    The ECM uses the speed density model to calculate airflow. The airflow tables are set points for desired airflow. If calculated airflow isn?t meeting what is set in the airflow table, the ECM adjusts the duty cycle to the wastegate solenoid to open or close the compressor vacuum pull to the wastegate to try to bring calculated airflow to the desired set point in the table. Simple as that. It?s not trying to regulate absolute pressure. The table would be defined in absolute pressure if that were the case but it?s not, it?s airflow. Airflow and air pressure are two different things.
    Last edited by Jim P; 11-02-2020 at 01:55 PM.

  10. #10
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    The ECM is trying to regulate Air/Fuel Ratio in the end.
    Last edited by Jim P; 11-02-2020 at 02:22 PM.

  11. #11
    the resason i keep refrencing absolute pressure is because i found a calculation online for mass airflow. it uses engine size, rpm,map,iat and # of cylinders. when i run the numbers from my log at the point my turbo hits 23lbs and stops the numbers match the map. I agree its not trying to regulate absolute pressure, but it seems its trying to regulate airflow by adjusting absolute pressure via the wastegate. am i way off? make sense in my mind
    05 qclb nv5600
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  12. #12
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    Well the wastegate redirects the flow of exhaust gases around the turbine, bypassing the turbine, reducing turbine speed which reduces compressor speed as they share common shaft thus reducing forced flow of air into the engine. Boost comes from the restriction of air flow, ie, when the cylinders and air intake between compressor wheel and cylinders are full and it begins compressing the air beyond atmospheric pressure. The turbo is basically a fan and fans have airflow and are commonly rated in airflow, even seem turbos rated in airflow that they can move, not pressure so it just makes more sense to stick with airflow.

  13. #13
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    looks like you've maxed out your MAP sensor, it's sitting at 255KPA desired 37psiA
    Last edited by JaegerWrenching; 11-04-2020 at 04:21 PM.

  14. #14
    I think I may have been reading my maps wrong which has gotten me confused. Concerning the maps on the tune, boost pressure fuel quantity limiter table for example. Is that scaled in absolute or gauge psi?
    when datalogging my master fuel correction would display boost p.f so i assumed i was hitting a boost limiter. But if my maps are scaled in psia then my mm3 is set to 144.973 at that boost level?
    I think i fell down the wrong rabbit hole... someone want to straighting me out?
    Last edited by bradshaw106; 11-07-2020 at 05:58 AM.

  15. #15
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    Boost in these ECMs is estimated via calculation. MAP-BARO=Estimated Boost. I?ve seen mixed opinion on the boost/fuel limit table but in my experience it coincides with the amount of pressure above atmospheric pressure, in other words, boost pressure. There is a limit to what the stock MAP sensor will read and your atmospheric pressure will affect how much estimated boost the ECM will calculate. In the scanner, the boost pressure PID is not boost pressure, it is MAP. It is super easy to verify tables ones self. For your boost/fuel limit table you set the fuel limit to a low number from 0-5 psi or something like that, test drive and datalog, review datalog and repeat till you determine what it coincides with.