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Thread: Generic jtec questions for hptuners support

  1. #1
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    Generic jtec questions for hptuners support

    Maybe this thread will stop a rush of questions to support.

    In the JTEC controllers, there are a lot of "units" missing when you right click. Are these going to be filled in?

    The cold warmup tables are listed as coefficients - are these simple multipliers - like percent - or are they pulse width adders or what? Are the map and time based tables additive?

    Same question about the PE table. Adders, FAR, pulse width, multipliers or what?

    Is the injector scaling "hard coded" as far as the math is concerned IF the PE table is FAR? Otherwise how would it know how much pulse width to command if it didn't know how much flow vs pulse width?

    Lastly, is there a way to turn off or re-scale the barometer update/learn when using a 2 bar map?

  2. #2
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    Coming from the SCT platform, the coefficients are multipliers of the base fuel table pulsewidths.

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    Maybe HPT can add TORR as the native unit for map as well.

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    I've been working on filling in some of the missing units. Most of the unitless stuff is multipliers.
    Eric Brooks
    HP Tuners, LLC

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    That's awesome!

    BTW page 10 in this pdf I found about JTEC PCMs gives a rundown of how this particular controller works.
    https://techauthorityonlinedemo.extr...8169999128.pdf

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    Thank you Eric!

    Looks like we have all of the answers except for how to handle barometer update with a 2 bar map.

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    Although that student workbook is full of a lot of useful information and insights into the operation of the JTEC engine controller, the block diagram is definitely not good information . This controller uses straight pulsewidth lookup with multiplicative and some additive modifiers . But generally speaking , assuming warmed up at sea level , steady state, open loop, your pulse width is : (injector offset + battery volt correction + fuel base EGR off (on)) * air temp correction factor, and if met PE qualifiers then * FA power enrich rpm based or part throttle enrich.

    Possibly counter intuitively , the altitude fuel table adds fuel as you go up in altitude typically. That?s because the fuel tables reference map directly, and the pumping efficiency of the engine goes up with altitude since the air density decreases, make sense ?

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    Quote Originally Posted by hexdummy View Post
    Although that student workbook is full of a lot of useful information and insights into the operation of the JTEC engine controller, the block diagram is definitely not good information . This controller uses straight pulsewidth lookup with multiplicative and some additive modifiers . But generally speaking , assuming warmed up at sea level , steady state, open loop, your pulse width is : (injector offset + battery volt correction + fuel base EGR off (on)) * air temp correction factor, and if met PE qualifiers then * FA power enrich rpm based or part throttle enrich.

    Possibly counter intuitively , the altitude fuel table adds fuel as you go up in altitude typically. That?s because the fuel tables reference map directly, and the pumping efficiency of the engine goes up with altitude since the air density decreases, make sense ?
    Thanks for that. It is counterintuitive for me at least.

    The question I'm trying to answer is what happens when at KOEO it takes a baro reading and sees about 2.5v, then you drive around and make some boost and it updates to something significantly different? Is it handled by simply making all of the atmospheric corrections 1 and basically eliminating altitude correction?
    Last edited by spoolboy; 10-11-2019 at 03:16 PM.

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    So I loaded my 2 bar tune and it started right up. The scanner is a little glitchy when starting it up, it doesnt like to load the PIDs, I have to disconnect and reconnect to the vehicle a couple times to get them to work. Other than that it works great. Just FYI, key on with a 2 bar sensor is 51kpa if that helps.

  10. #10
    Quote Originally Posted by jasond29 View Post
    So I loaded my 2 bar tune and it started right up. The scanner is a little glitchy when starting it up, it doesnt like to load the PIDs, I have to disconnect and reconnect to the vehicle a couple times to get them to work. Other than that it works great. Just FYI, key on with a 2 bar sensor is 51kpa if that helps.
    This is something I'm working on, I've noticed it as well. Not 100% sure why, but Im working through it!
    If its not broke, just give it time.

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    It learns baro at key on and then relearns when map exceeds baro or if you are going down in altitude, past a specific throttle angle. Problem is, this only works with a one bar map sensor. You will find that if it learns 51 KPA when the car starts, it will relearn to whatever map it makes when you start making boost.

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    totally understandable, work in progress. I took my car out for a little bit of testing and I believe this has been one of my best purchases yet. Already got the fuel trims within 5% and no more fuel smell or dead spots in the part throttle. I have a innovate wideband and using the serial I cant seem to get that to log but I am sure its probably something I havent configured. I am just blown away how quickly I was able to improve the drivability, idle is perfect, starts great and no dead spots.

    I was curious as to what PIDs are supported for the JTEC, is it just the 10-12? I would guess that this is a limitation with the ECU and not hptuners scanner.

    Anywho I am kinda bummed now cause I really have no real tunning to do now that it is running so well. I guess I will pulley the blower down and see what it can do.

    I know there are no plans for custom OS but I would be a huge supporter if you did, would love to run 20lbs of boost, E85 sensor, 2 step and other such stuff

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    Quote Originally Posted by hexdummy View Post
    It learns baro at key on and then relearns when map exceeds baro or if you are going down in altitude, past a specific throttle angle. Problem is, this only works with a one bar map sensor. You will find that if it learns 51 KPA when the car starts, it will relearn to whatever map it makes when you start making boost.
    Yes mentioned in another JTEC thread but is there a way to prevent it or get around it? Although it sounds like jasond29 may have figured it out.

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    I dont see how it could use the MAP to relearn BARO when there is a load on the engine. All I know is I divided anything that references the MAP by 2 and I dont have any problems. I did multiple pulls in boost (8lbs) and cruised around for about an hour in different conditions (stop and go, highway) and never had any issues. I can only speak for my platform, 2000 viper JTEC, maybe other platforms have a seperate sensor to read BARO but if it uses the MAP I can only see it being utilized at key on, none running conditions.

    Coming from GM LS tuning, when you went to speed density, which is essentially what the JTEC is using, your tune would fluctuate because there is no MAF that worked in conjunction with the MAP to determine BARO. Key on determines BARO and it will stick with that until engine is cycled again and get a new reading. Again that has been my experience with my vehicle.

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    According to the JTEC workbook the MAP is used for Baro relearn. I if you have a BARO PID you can check if it drastically changes.

    "The MAP Sensor input is the number one contributor to pulse width. An important function
    of the MAP Sensor is to determine barometric pressure. The PCM
    needs to know if the vehicle is at sea level, or in Denver at 5,000 feet above sea level,
    because the air density changes with altitude. It will also help to correct for varying
    weather conditions. This is important, because as air pressure changes, barometric
    pressure changes. Barometric pressure and altitude have a direct inverse
    correlation; as altitude goes up, barometric pressure goes down. The first thing that
    happens as the key is rolled on, before reaching the crank position, the PCM powers
    up, looks at the MAP voltage, and based upon the voltage it sees, it knows the
    current barometric pressure relative to altitude.

    Once the engine starts, the PCM looks at the voltage again at the trailing edge of the
    last slot on the current cylinder and the leading edge of the first slot of the next
    cylinder. These two values are added and then divided by 2 to get an average. It
    then averages these signals and compares the current voltage to what it was at
    key–ON. The difference between current voltage and what voltage was at key ON is
    manifold vacuum

    During key–ON (engine not running) the sensor reads (updates) barometric (Baro)
    pressure. A normal range can be obtained by monitoring a known valid sensor.
    As the altitude increases, the air becomes thinner (less oxygen). If a vehicle is
    started and driven to a very different altitude than where it was at key ON, the
    barometric pressure must be updated. Anytime the PCM sees at least 1.8 volts
    above minimum TPS, and based upon rpm, it will update barometric pressure in the
    MAP memory cell. With periodic updates, the PCM can make its calculations more
    effectively. Also, if MAP is ever greater than Baro, such as coming down from a high
    altitude, Baro automatically updates."

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    ok, makes sense. There is an altitude table that I did change, its under engine/power enrich/part throttle/alt correction. The axis are rpm/barometric pressure. The stock file barometric pressure ranges from 60kpa to 99kpa, which is basically idle to WOT. I did change the range of the BARO columns to 30kpa to 52kpa. I honestly just made this change since I have had the hptuners software and like I said I have driven the car for about a hour. Time will tell if this is correct because to be honest with you I dont know if it is. I did get into boost several times.. and everything seem to run as advertised. I believe the BARO will only effect part throttle cruising, WOT is set in stone and uses static parameters as far as I can tell.

    This is a learning experience for all of us I guess..... I am by no means an expert and hope to see more input on JTEC tuning as we go.

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    jasond29, I have to disagree with your last post. Certainly if you are satisfied with your end result that's fine. I only want to clarify this point so that other people are not confused or misinformed with your comment and conclusion.

    JTEC uses the same OS regardless of model. I have some knowledge of JTEC because because my specialty has been tuning Gen 1,2 and 3 Vipers for many years, starting several years before commercial tuning software was available. The BARO multiplier is being used all of the time. I've seen tunes where baro has not been addressed, and it does move around, enough to cause cars to lean out dangerously. It's very likely in your instance that the shift if fuel mixture is not enough to cause a drivability issue that you perceive, or your baro update happened early enough in your driving so you wound up tuning around it, however if you had logged baro and map, from startup to into boost, you will see that, as I mentioned previously, the baro will re-learn to the highest map value, simple as that. Also as Homer pointed out, this is explained in the training manual just the same.



    From the screen shot below you can see what happens when you go from your key on baro of 51kpa to a "JTEC interpreted" map value of 87kpa, it leans out the fuel mixture by about 11%.

    jtec altitude fuel correction table.JPG

    Here is a log of baro learning going up in altitude:

    JTEC baro update example going up in altitude.JPG

    And down in altitude:

    JTEC baro update example going down in altitude.JPG

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    So like spoolboy suggested I guess you could set the baro table to 1's as it is a multilpier (0's if it is an adder)?

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    Quote Originally Posted by jasond29 View Post
    I did change the range of the BARO columns to 30kpa to 52kpa. I honestly just made this change since I have had the hptuners software and like I said I have driven the car for about a hour. Time will tell if this is correct because to be honest with you I dont know if it is. I did get into boost several times.. and everything seem to run as advertised.
    I beleive this may be the best way to handle this.

    I was able to edit the row axis by highlighting the whole axis and choosing X .5
    That may not be 100% correct based on map scaling, but it confirms that it lets you do it.
    Last edited by spoolboy; 10-12-2019 at 12:40 PM.

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    Maybe I am understanding this wrong, but I don't see how rescaling baro range circumvents the fact that the PCM can relearn baro. Basically the baro value would be bouncing all over the place except for initial startup so I don't see how one can usefully use the baro table?