Trying to get idle and cold start set

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  1. #1
    Senior Member Array torchred04's Avatar
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    Default Trying to get idle and cold start set

    So I got my car running again with the ID1000's, VMP big TB and crusher inlet on my 3.4L Whipple.

    I have a couple questions and need some help/guidance.

    So I have the IAC off the side of the whipple inlet right now. For some reason I used a 1/2" hose, I am wondering if this is too small now and I need a 5/8" hose?

    Next question. The car will crank over, catch and fire but the idle comes up and then drops down low and stalls unless I give it throttle input. After its ran for a few seconds I can let off the throttle and it will stay running.

    I did swap to the lower vacuum opening bypass valve from whipple and tested it with a vacuum tester before putting the blower on the car and it was opening up.

    To rectify this I am assuming its due to the motor not getting enough air through the IAC valve or its pegged and I have to open up my throttle body blade more?

    If its the throttle body blade should I be unhooking the IAC sensor so it does nothing and trying to set the idle via the throttle stop screw until the car will idle?

    Any help would be appreciated. I am working with pro racers myself this time and I have a base file to help but if you have any tips on items in the tune I should be focused on please fire away.
    Last edited by torchred04; 08-21-2017 at 11:01 AM.

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  3. #2

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    Schyler,

    A high IAC duty cycle is indicative of too small a throttle blade air gap. In the old days Accufab (and others) used to tell everyone that you should not move the throttle stop positioning from where they shipped it. This was good with stock cams at 114˚ centerlines. As we went to larger aftermarket cams, tighter centerlines and more overlap our idle vacuum went away and so did our nice idle. Some guys did this intentionally because they were trying to mimic the 60's muscle car idle sound. Others just got ambushed by their cam choices.

    If the engine is idle vacuum challenged you will need to both open the throttle blade more at idle and raise your idle speed to maintain good idle manners. As you begin to open the throttle blade the IAC duty cycle will decrease. Something to be attentive to is only use Ford IAC motors. Ford's IAC motor is a frequency based unit and the aftermarket units are by and large voltage based units. If you put a non frequency based IAC on our engines they will not work at all and things will get confusing fast!

    If you have not already I would go into the tune and set the idle to 850 rpm if it is not there already. Start opening the throttle stop and go in quarter turn increments. Data log your IAC motor duty cycle. Continue to open the throttle blades until the idle rises above 850 rpm. At that point stop, shut off the engine and down load the data log.

    Look at your IAC duty cycle. Different guys have different favorites. I like to see a 30% duty cycle. The normally gives the IAC enough wiggle room to manage the airflow up or down to maintain your target idle. If you have a big cam when you start to open the throttle blades the idle will go above 850 without significantly dropping the IAC duty cycle. If this happens to you the car is telling you it wants to idle higher. Don't get crazy with idle speed. Go into the tune and step it in small increments say 100 rpm and begin the process all over again.

    My bet is it should sort out nicely at right around 850 rpm. Once you get the throttle position where you want it for the 30% IAC duty cycle, if you want a lower idle try lowering the idle RPM in the tune by 100 RPM and resetting your throttle stop to get back the 30% IAC duty cycle you were targeting. This lower idle is not always possible so don't get your hopes up too much.

    Always use your data logging capability to let you see what is happening as you are closing in on your target IAC duty cycle. If you want and your camshaft will cooperate you can sneak even lower in the idle RPM. I tend to like a 750 / 850 idle, especially with cams because it keeps the plugs cleaner. Big cams and low idle speeds (<850) tend to foul plugs and create bad low speed driving manners.

    This approach should fix your IAC duty cycle / throttle stop headaches. Let me know how it works out for you.

    BTW the 1/2 inch hose should be adequate, a 5/8 hose does no harm but is overkill. Before you start the hose swapping try the idle stop setting technique above.


    Ed
    Last edited by eschaider; 08-21-2017 at 05:51 PM. Reason: Spelling & Grammar

  4. #3
    Senior Member Array torchred04's Avatar
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    So I unhooked the IAC sensor once at temp and started increasing my throttle blade opening position till I got the car running with no IAC connected. It took a lot more opening then I expected but I had it idling around 850-900rpm with no IAC hooked up.

    I then plugged the IAC back in and to my surprise the ISC duty cycle was still at 0.54 for a value and my idle increased to around 1200 rpm. I shut the car off and went and reposition my TPS sensor so the AD counts key on car off was back at 190-192 vs 210. This brought idle when sitting down to 1130-1150 range but duty cycle on my ISC was still 0.52-0.54 range. My commanded desired idle was 800rpm in my tune.

    I am wondering if when Eric built my file he increased the air demand on the ISC neutral idle air to a higher value to force the IAC open more? I took 10% out of the ISC Neutral idle air across the board and will try starting it again tonight to see if the rpm comes down some. If it does then I need to keep scaling that down till its around 800-850rpm at idle. I am hoping reducing the ISC Neutral idle air will drop my ISC duty cycle, but I am new to tuning and not sure if that is what effects the ISC duty cycle in the tune?

    If my ISC duty cycle stays at 0.52-0.54 then I am guessing my IAC sensor is stuck and needs replacing.

    What are your thoughts?

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  6. #4
    Senior Member Array torchred04's Avatar
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    Have any of you adjusted the Airflow Through Throttle body value from 0.334 to a larger value in the Advantage III software?

    I just logged my #/min MAF PID with my IAC sensor unhooked and the car idling around 750-800rpm on its own(a bit rough) and I logged an average of 373.022 #/min

    Not sure how I enter that value into the advantage software as you are allowed from 0-2 for a value input.

    I have the big VMP TB on my car.

  7. #5

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    I don't know if it's applicable, but what I do a lot of times is calculate the % under/over the stock number(s) then apply that as a correction factor to the appropriate scalar or table. It seems to work well with flow numbers, volumes, etc...

  8. #6

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    Schyler, I suspect that there might be an error in your calculation. A cubic foot of air at STP weighs 0.0807 lbs. 373 lbs of air would be the equivalent of 4622 cubic feet of air at idle. To get a sense of the enormity of this number if you look at the front page of the Fuel System Calculator and plug in a 'little' 2.3L blower with a 7.4" lower and a 3.5" upper it will flow 2216Kg/hr at 8000 crankshaft rpm. 2216 Kg/hr is the equivalent of 4885 lbs/hr or 81 lbs/min of air.

    The calculations you have suggest the engine is consuming more than 4.5 times the amount of air at idle that a 2.3L blower at ~17,000 rpm pumps. I suspect that there is a dimensional or other calculation error that has produced this unusually large number. If I remember correctly the value in my tune for the Throttle Body Air Flow was ~9.12 Kg/hr at idle and (if I remember correctly) yours was ~9.33Kg/hr. With the your aftermarket throttle body, your increased air gap and the aftermarket cams my guess is that this number should be in the neighborhood of ~10Kg/hr (maybe a little higher) in your tune.

    I suspect it would be worth the effort to take the airflow measurement one more time. If your MAF xfer function reads in Kg/hr you can read the number directly. If it is in other mass units/min or other time metric you will need to convert to get to the Kg/hr figure you need. Take you time. Finding the number you are looking for can be maddening, particularly if you move too quickly.


    Ed
    Last edited by eschaider; 08-23-2017 at 02:16 AM. Reason: Spelling & Grammar

  9. #7
    Senior Member Array torchred04's Avatar
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    Here is my log file. On livelink I found under MAF the MAF #/min PID and logged it directly. The units it gave me were #/min you can see on the log and its 373 #/min average.

    Is this suppose to be reading 0.373?

    EDIT: I can't seem to attach my .csv file, PM me your email Ed I will send you the file.

  10. #8
    Senior Member Array torchred04's Avatar
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    Should add I got this all fixed up.

    I ended up unhooking the battery with the headlight switch on for 1-2 days. Hooked it back up, made sure TPS voltage was 0.98 key on car off. Put the neutral idle air table back to stock values and input the logged airflow at idle with the IAC valve unhooked into the airflow across TB spot.

    Car starts and idles well now at 800rpm +/- the usual flutter with a ISC duty cycle of around 0.26-0.40 once warm depending on the engine temp.

  11. #9

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    Apologies for disappearing on you Schyler. We had friends and family in Houston and Florida. It has been sort of nip and tuck. Houston turned out OK but Florida not so much. Glad you found the bad boy and those numbers you are measuring are right in the hunt where they should be.


    Ed

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