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  • chts discussion, enriching trick?

    I'll just paste this from another forum so we can argue with references easier

    Crowbar60
    post Jun 25 2005, 02:07 PM
    Post #97


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    You should try the throttle body potentiometer pot trick if you have one. KA24e throttle bodies have rotary pots as well as TPS. The pot can be made to trick out the cyl head temp sensor. As the throttle is opened, the rotary pot in parallel will change the sensed chts (seeing a cooler head). The ecu will jump up the fuel and timing as if the car was cold.
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    mc
    post Jun 27 2005, 09:54 AM
    Post #98


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    ....thanks for the tip....your talking about the TPS which has the extra wire/connection attachment???splice this TPS connection between the stock CHTS and harness???
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    Crowbar60
    post Jun 27 2005, 11:10 AM
    Post #99


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    Yes its the extra connector that many KA24e have. But I am specifically using a Stanza KA24e early 90s throttle body. The TPS is a limit switch setup and the potentiomer is a rotary varying resistance. An interesting thing is that California 300zx (at least the 88 ) have potentiometers as well as TPS.

    On my potentiometer, there are three wires running to the connector. The wires are red, white and black.

    If you have a chts that works, you will want to have a switch that interupts this connection when the car is cold started. This is because the ecu needs to see a high resistance from the chts when its cold.

    If you have a multimeter, measure the potentiomers resistance looking into the red and black wires as you move the throttle. You should see a varying resistance as a function of throttle opening. I will measure the resistance and how it interacts with the chts negative response thermsitor characteristic but I am only basing this on my own throttle pot resistance range. Measure resistance between red and black, red and white, white and black and do it at idle and full throttle for all cases.

    The trick is that the ecu will respond to the 'chts' resistance as it varys with throttle opening. The ecu is fast enough to take this into account. As the throttle opens, the fuel curve will be set for a cooler head temp. The timing will also be advanced.

    Another trick with TPS is to get one for a auto tranny car (if you have a stick car of course) and use the throttle position switch (TPS) signal for full throttle position (stick cars TPS have only off idle switch not full throttle).

    The full throttle position can then be made to trick out the fuel temp sensor. The fuel temp sensor is similar to the chts in that its a negative going resistance with heat rise. You would want to 'trick' this sensor by making the resistance seen to be 'hotter' than it actually is. The ecu compensates for hot fuel by enrichening the pwm of the injectors. I imagine this can also be done in parrallel with the parallel connection only being made under full throttle. A resistor sized to appear (or make the parallel connection appear) 'hot' gets kicked in.

    This is all simple stuff and can be done for pennys. The one thing you do not want to do is have a break or discontinuity in resistance seen. This will trigger an error signal. The ecu must be fooled that somehow resistance has changed and it must respond according to its program.

    Edit: I will post a wiring diagram
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    Crowbar60
    post Jun 27 2005, 01:12 PM
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    This is the temp response of the chts thermistor. If you unplug this and measure into it you should see these resistances under these temp conditions

    20 C 68 deg F (2.3Kohm-2.7 kohm)
    50 C 122 deg F (770-870 ohm)
    80 C 176 deg F (300-330 ohm)

    Note the resistance goes down as the temp goes up.

    If your car is 'cold' and the temp outside is around 70 deg F, then your measurement should be in the 2.3-2,7Kohm range. Drive your car and get it up to temp. Unplug and measure again. It should be around 300-330 ohms.

    If its open (Megaohms) or nearly zero (short) then you have a bad chts. They are a pain to change.

    I run without it. I wire the leads directly into the throttle pot. At idle my car thinks its getting 770 ohms or around 122 F. At full throttle it thinks its about 40 below. To start my car, I give it a slight 1/4 throttle opening (increases resistance and car sees 'cold') and it fires. I use the black and white wires.

    When I wanted to get an emissions test, I layed a 500 ohm resistor across this in parrallel. Car passed easy. This made the 'seen' resistance around 300 ohms pretty much across the throttle opening range.

  • #2
    Modification of the CHTS to achieve enrichment is not only stupid, it's down right obsolete.

    Even the engine temp and cold start enrichment values added into the ultimate injector pulsewidth calculation cannot exceed the TTPmax setting anyway! This is the limiting factor on fueling.

    This means it gives you more fuel where you DON'T need it, and no more fuel where you DO need it.

    With what we have learned about the Nissan ECCS ECU's in the last few years, as I said before, I can look at this and say it is a completely misguided attempt to accomplish an end result that can easily be accomplished (with no ill side effects) with a socketed ECU and edited code on an EPROM.

    Someone doing this mod would have no idea of the logic the ECU uses. You would be far better off raising the fuel pressure a few PSI.

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    • #3
      But it is soooo simple, and costs pennies. :wink:

      Terrible idea putting those wheels on...

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      • #4
        I think part of the reason was to allow you to bypass the chts.... however a dinky resistor would work nicely too, your car would alwyas see a steady state temperature

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        • #5
          G-E cut and paste some old info. I have actually developed that idea further.

          But Jason, you seemed perturbed by this, yet you like shoving cut up sodey bottles crammed in MAFs????

          http://www.redz31.com/forum/viewtopic.php?t=622
          Try not to be a Yahoo

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          • #6
            crowbar wrote: G-E cut and paste some old info. I have actually developed that idea further.

            But Jason, you seemed perturbed by this, yet you like shoving cut up sodey bottles crammed in MAFs????

            http://www.redz31.com/forum/viewtopic.php?t=622

            I didn't see your name on there before.

            What you have there are two methods with major flaws. Any sort of maf bypass or voltage reduction is going to accomplish an open-loop enleanment in the end. The problem with tricking the CHTS resistance supplied to the ECU is that it simply WILL NOT WORK to correctly enrich the fuel mixture when the maximum injector duty cycle has already been reached.

            Edit2: Forget what I said before, I would like to see your data on how you have it set up for transient enrichment.


            Edit:

            It IS an interesting idea for transient throttle-based enrichment, but it can't be used when the fuel injecotor maximum has been reached.

            The simple band-aid solution is to tune the fuel map cells in those transient partial-throttl load areas on the rich side.

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            • #7
              I'm sure you're right about hitting the wall, but up until that wall it could serve as a cheap hack.... that said as you know it's a very minor adjustment, something the o2 sensor could counteract anyway

              but then you ecu fuddlers have learned more about the precise effects each condition change has than I so I just wanted to see what you/bernardd/stinky would say

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              • #8
                Someone doing this mod would have no idea of the logic the ECU uses. You would be far better off raising the fuel pressure a few PSI.
                This is incorrect. I assume you mean across the rpm range.

                The ecu will learn this closed loop and factor it out through O2 sensor feedback.

                You might mean a variable fuel pressure system like the BEGI I hope.
                Try not to be a Yahoo

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                • #9
                  crowbar wrote:
                  Someone doing this mod would have no idea of the logic the ECU uses. You would be far better off raising the fuel pressure a few PSI.
                  This is incorrect. I assume you mean across the rpm range.

                  The ecu will learn this closed loop and factor it out through O2 sensor feedback.

                  You might mean a variable fuel pressure system like the BEGI I hope.
                  Incorrect again. You keep saying the ECU learns. This is false. The Z31 and all Nissan ECU's prior to 1990 have no adaptive self-learn mechanisms that are commonplace on OBD2 PCM's. Even the later nissan-branded consult units have very little, only in the form of additional knock-mode fuel and timing maps.

                  The ECU will correct for the increased fuel in closed loop mode, but when you go back into open loop (aka stepping on the gas) the ecu simply reverts to the parameters it is programmed with, meaning a fuel pressure change will always result in a richer mixture when under boost or in any open-loop operation mode!

                  Back to the topic: You say you have developed the idea further, I would like to hear more.

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                  • #10
                    The words "cheap" and "fuel" even in the same scentence means nothing but trouble if you ask me!
                    http://youtube.com/c/zcartube

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                    • #11
                      crowbar wrote: Hi, i am crowbar, i like arguing
                      Don't mind me

                      Terrible idea putting those wheels on...

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                      • #12
                        well I'll say this for the guy, he might be a moron but he's forcing us to discuss some advanced topics at great length, and this is a good thing for the other visitors

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                        • #13
                          true...

                          But attitude is a key element in discussion, at least in my perspective.

                          Terrible idea putting those wheels on...

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                          • #14
                            I would love to discuss further, Will the Butt-kizz-iss ring in every time or can you calm them down?
                            Try not to be a Yahoo

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                            • #15
                              crowbar wrote: I would love to discuss further, Will the Butt-kizz-iss ring in every time or can you calm them down?
                              If you make valid points based on fact and reason, I don't see why we would have the whole thread going on. Tactfully wording responses for some slightly sensitive topics you hit on would not have prompted that.

                              The fact is I did not see the potential of integrating a resistor because of the way fuel enrichment is accomplished. I see using a POT on a TPS like this and altering the resistance very slightly, for a short period of time to be a fair compromise for getting a system in place very similar to standard TPS-based acceleration enrichment (or accelerator pumps on carb'd cars).

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