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Thread: how to actually adjust TPS voltage?

  1. #1
    Senior Tuner DSteck's Avatar
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    how to actually adjust TPS voltage?

    I've tried searching, but cannot find anything on this.

    I started working on a 2001 Formula last night that just had a cam and heads done. Small cam... 227/231 (0.61X/0.61X lift though) and ported 243s. One thing to note... it idles like it has a much bigger cam, which I can't figure out why.

    Anyway, the TPS is giving me hell. At hot idle, IAC counts were around 70 and it was idling at 850. I did the idle air config and plugged in the base running airflow. I shut it off, tried to start it again... it'd hit, and then die. I cracked the blade open a little more, and it fired up and idled perfect. IAC counts dropped a little bit (about 60), and TPS was reading 1%. I tried to reset the TPS by unplugging it, turning the key on, wait, key back off, plug it back in, try again... It wouldn't reset.

    I wasn't going to worry too much at this point, but it kept wanting to die if you revved it. For kicks, I forced the IAC counts to 100 and revved it... settled back down to idle perfectly. Next, I just unplugged the TPS and adjusted the set screw to get IAC counts down to 40. It idled perfect, and wouldn't stall out at all. The problem though is the TPS wants to read 2% at this point, so it ends up idling high.

    I tried resetting the TPS multiple times, but it won't reset. I'm pretty sure I need to adjust the actual voltage of it. However, I've been having a hard time finding instructions on how to do that. Can anybody explain how to properly adjust the voltage at closed throttle?

    What's really tripping me out is I've done about eight cable throttle cars in the past two weeks, and not a single one did this crap. All of them would reset the TPS and idle/recover perfectly... even some MS4 and T-Rex cammed cars. The only thing different about this car in question is it's an automatic. It won't stall out if it's in gear... only in neutral.

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  2. #2
    Tuner in Training
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    TO adjust the TPS voltage you have to make the monting hols on the TPS sensor oval so it can be rotated a little. I recommend you just drill a hole in the blade or make it a little bigger.
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  3. #3
    Senior Tuner Frost's Avatar
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    IAC position is the final calc and sum of all values in the airflow 'soup'. If you can force it somewhere and get desired results then it can be tuned to work. You have adders such as the TF to let it settle back down to idle in park/N independent of gear. They must come in and be decayed to 0 just before the RPMs reach the idle area or they will keep adaptive idle from running (watch STIT activity).

    If you had the counts at 70 at hot idle, while a little high, it's workable. The fact that it didn't want to start without opening the blade is not all RAF. Instead of opening the blade, you add startup airflow, hold it for an appropriate time and then get it decayed out.

    If you can't get the counts lower and get it to reset to 0.4% or less (o.8% or the TPS 'flicker' is NOT ok) every time, you will have to drill the blade hole. It happens every now and then.
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  4. #4
    Senior Tuner DSteck's Avatar
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    Quote Originally Posted by Frost View Post
    IAC position is the final calc and sum of all values in the airflow 'soup'. If you can force it somewhere and get desired results then it can be tuned to work. You have adders such as the TF to let it settle back down to idle in park/N independent of gear. They must come in and be decayed to 0 just before the RPMs reach the idle area or they will keep adaptive idle from running (watch STIT activity).

    If you had the counts at 70 at hot idle, while a little high, it's workable. The fact that it didn't want to start without opening the blade is not all RAF. Instead of opening the blade, you add startup airflow, hold it for an appropriate time and then get it decayed out.

    If you can't get the counts lower and get it to reset to 0.4% or less (o.8% or the TPS 'flicker' is NOT ok) every time, you will have to drill the blade hole. It happens every now and then.
    I'm just shocked because it's such a small cam, and the car is otherwise totally stock... and I haven't had this problem before.

    I guess I will try pushing the startup airflow and follower around. I did notice that follower decays out extremely fast. I've never used the follower heavily (only recently got into cable throttle stuff), and this guy is absolutely rushing me to get this car out the door.

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  5. #5
    Senior Tuner Frost's Avatar
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    Cams in that area can be a bear every now and again for whatever reason... maybe the DCR, who knows. If you free rev using different levels of throttle and it doesn't return to idle well, it's follower. It can be counter intuitive because too much follower delays adaptive idle. Too little and adaptive idle comes in before the RPMs settle and it goes negative to where it should be causing the dip. Too much and adaptive idle doesn't kick in until you are beneath target. You need to run the range of TPS on it as well.
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  6. #6
    Senior Tuner DSteck's Avatar
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    The harder I stab the throttle, the worse the recovery is. If I force the IAC to 100 counts, or crack the blade to where IAC counts are at 40 and unplug the TPS, it'll return to idle absolutely perfect every time, in neutral or in gear.

    Can you explain "run the range of the TPS"? Do you mean check voltage at closed throttle and full throttle?

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  7. #7
    Senior Tuner Frost's Avatar
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    The worst PITA setup I ever tuned GenIII was a small-ish 232/235 112LSA Cam-motion custom and TEA ported OEM castings that were about 60cc chambered. Even getting IAC down to 20 counts at hot idle, there is not enough IAC volume to start the car below 65degF outside temp without touching the pedal to open the blade. It's at 310 counts at cold start and just not enough air. I have MS4 cars (much larger cam) that start in 20deg just fine and don't need all of that IAC.
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  8. #8
    Senior Tuner Frost's Avatar
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    Quote Originally Posted by DSteck View Post
    The harder I stab the throttle, the worse the recovery is. If I force the IAC to 100 counts, or crack the blade to where IAC counts are at 40 and unplug the TPS, it'll return to idle absolutely perfect every time, in neutral or in gear.

    Can you explain "run the range of the TPS"? Do you mean check voltage at closed throttle and full throttle?
    Log STIT's so that you can see adaptive idle. Log TF as well. Hit the gas, watch it add follower and watch the follower decay as RPMs drop. The follower table adds more as TPS increases. Start with light blips and get it decayed and into adaptive smoothly (STIT's begin updating from 0) and work your way the TPS (follower adder) range until you can stab it and get a smooth recovery to idle.
    Steve Williams
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  9. #9
    Senior Tuner DSteck's Avatar
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    Quote Originally Posted by Frost View Post
    The worst PITA setup I ever tuned GenIII was a small-ish 232/235 112LSA Cam-motion custom and TEA ported OEM castings that were about 60cc chambered. Even getting IAC down to 20 counts at hot idle, there is not enough IAC volume to start the car below 65degF outside temp without touching the pedal to open the blade. It's at 310 counts at cold start and just not enough air. I have MS4 cars (much larger cam) that start in 20deg just fine and don't need all of that IAC.
    Yea, I just worked on a MS4 cam the other day in an S10 and built a base file for it... Car fired up instantly and idled, and recovers to idle no matter what you do. It just won't stall out.

    This car I'm working on fired up and idled perfect cold with the throttle body where it was. Counts were in the 180 range. When it got hot, counts went to about 70, but it wouldn't restart with where the throttle blade was adjusted to. That's when I started cracking the blade and running into the issue of the TPS not resetting. Like I said, if I could get the damn TPS to read 0% then the thing would be perfect. I might try grinding out the slots and clocking the TPS.

    When tweaking the follower, do you mess with the delay at all? Or just the airflow values? When I was doing that yesterday (watching follower), the airflow was gone almost immediately from it.
    Last edited by DSteck; 10-28-2010 at 12:31 PM.

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  10. #10
    Senior Tuner Frost's Avatar
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    Yes, usually reducing it in gear to 0 at 0MPH. It's already zero'd in P/N. Typically I have to up the decay rate at 0MPH and reduce the large jump the base airflow table makes at around 13.5% You want all follower decayed to 0 just above commanded idle.
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  11. #11
    Senior Tuner DSteck's Avatar
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    Gotcha. Greatly appreciate you taking the time to help me out and explain things.

    I still want to try either drilling the blade or clocking the TPS first instead of trying to work with an existing condition.

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  12. #12
    Senior Tuner Frost's Avatar
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    No worries. Even if the blade gets drilled, this a normal part of tuning for many cammed setups.
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  13. #13
    Senior Tuner DSteck's Avatar
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    Ok, here's another generic question for you Frost...

    I slotted the TPS and reset it so that it reads about 0.63V with the blade cracked to where IAC counts are about 50 at idle in neutral. It allows me to reset the TPS as well... So I played with follower, and it's perfect in neutral Never dips below idle, comes right back down perfectly.

    As soon as you throw it in gear, it gets unreliable. The car has a massive 4000rpm stall, so I can't imagine it's really pulling it down that hard. If you blip the gas, it'll come back to idle just perfect. However, when you really lean into the pedal and let out, it will want to die. From watching throttle follower, it still has follower air when it dies.

    It doesn't even act like it wants to come back to idle. It just tanks out hard. Any idea? I know, I know... post a log and the tune. I don't have those right now. Haha.

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  14. #14
    Senior Tuner Higgs Boson's Avatar
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    For me that sounds like all TF but we all know I'm a newbie. I would add a bit and check.

  15. #15
    Senior Tuner Frost's Avatar
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    It is follower; it needs to be fully decayed out just above idle set point so that adaptive idle can take over. This is under assumption that you are not moving here.
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  16. #16
    Senior Tuner DSteck's Avatar
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    Quote Originally Posted by Frost View Post
    It is follower; it needs to be fully decayed out just above idle set point so that adaptive idle can take over. This is under assumption that you are not moving here.
    Rolling or sitting still, it'll die in gear. Apparently it randomly started dying in park/neutral too. I spent a while getting it perfect in park/neutral, but don't understand why all the sudden it's dying in park/neutral. I assume at this point I have to start pushing the decay values around.

    It's acting exactly like it's just running out of air. I'm beginning to wonder if something is mechanically wrong, but can't even think of something feasible.
    Last edited by DSteck; 11-01-2010 at 01:56 PM.

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  17. #17
    Senior Tuner DSteck's Avatar
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    So Frost, I've noticed that the follower table takes off after 13.5% TPS. Do you typically just knock this value down to whatever is in 13.5% as a starting point? I'm working with this car again today and just want to be prepared. Apparently it's been dying more often now. I'm going to re-adjust the idle some more... I've found it's easiest to just unplug the TPS and play with idle, THEN mess with getting the TPS voltage correct (which I've found is actually really easy).

    I just want this damn car to be done.



    In other news, I tuned an MS4 in an S-10 LS1 swap with a TH-350 and 5000 stall. Maybe this is related. Unfortunately, the PCM doesn't have a vehicle speed signal. For the cam, the engine idles awesome and settles back to idle perfectly, in neutral or drive. However, it isn't a manual valve body transmission, so if it upshifts, and then you try slowing to a stop, you can feel the transmission drag the engine down and stall it out. If the trans kicks down into 1st, it'll come back to idle flawless... but if it stays in 2nd or 3rd, you can just watch the engine speed drop as vehicle speed comes down. Is there any way around that without getting a speed signal to the PCM or gear signal?

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  18. #18
    Senior Tuner Frost's Avatar
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    That first step-up in follower around 13.5% is typically too high and will leave follower active to a lower RPM point than you would want, which as stated, keeps adaptive idle from happening. I also zero out LTITs. If they are negative, they will have an immediate impact (closing IAC) as soon as adaptive begins, and that can cause stalling.

    The only time I ever play with (unplug) TPS is to reset it after adjusting the blade.

    I have tuned a few without VSS's but I generally try to get the customers to get SOME kind of scalable signal back to the PCM for MPH reference.
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  19. #19
    Senior Tuner DSteck's Avatar
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    Gotcha. I'm still just shocked this one is so different. I've never had to touch anything regarding startup or friction airflow, yet this car won't start unless the base running airflow is about 0.2 lb/min higher than desired airflow. Every other car I've done fires up flawless and perfect when base running airflow matches idle desired airflow. This one just won't, so it always has a pretty strong LTIT. If I disable LTITs, it wants to hang after startup. They won't leave the car with me either, so it's annoying having to make multiple trips and shoot the breeze while trying to work.

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  20. #20
    Senior Tuner Frost's Avatar
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    Every cammed car that I have ever tuned has had startup airflow added and the decay and delay adjusted. If you get hang with LTITs disabled, the base airflow is too high.
    Steve Williams
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