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Thread: Sniper EFI IAC issue.

  1. #1
    Join Date
    Nov 2016
    Location
    St Louis
    Posts
    15

    Default Sniper EFI IAC issue.

    Hi all. I'm really struggling with IAC. I set it at 2% during hot idle, and after driving for awhile the value will creep up to a large number (20-50%). This drives the idle up by ~1000 RPM (IAC Ramp Start = 1000?). It never comes back to the desired hot idle speed. My IAC Hold Position is 15%, my IAC Ramp Decay is 2 sec, and my IAC Kick is 10% (no A/C). My IAC speed is set to Slow.

    Two other things to note:
    1) I'm using a mechanical + vacuum advance distributor, so I've disabled spark control.
    2) My WBO2 sensor may be 4-5 inches forward of where it should be.

  2. #2
    Join Date
    Dec 2009
    Location
    Connecticut
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    19,283

    Default

    Quote Originally Posted by j_reins View Post
    I set it at 2% during hot idle, and after driving for awhile the value will creep up to a large number (20-50%). This drives the idle up by ~1000 RPM...
    That's strange. The IAC Position % is supposed to decrease as engine temperature stabilizes. What's the TPS Position % when this happens?
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  3. #3
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    Nov 2016
    Location
    St Louis
    Posts
    15

    Default

    The TPS Position % value is a solid zero at idle.

  4. #4
    Join Date
    Dec 2009
    Location
    Connecticut
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    What happens if you temporarily block off the IAC air inlet port with your finger or a strong piece of tape? Does the engine consistently idle good?
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  5. #5
    Join Date
    Nov 2016
    Location
    St Louis
    Posts
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    If the IAC is large-ish, blocking the IAC air inlet will cause the car to stall (at idle). If I attempt to adjust the idle screw toward 2%, the RPM will run away high, then slowly come back, but it won't come back to desired hot idle. So what I've done is get the temp hot (in the learning range), and re-run the Wizard. This allows me to reset IAC to 2% with a stable desired hot idle, but now I'm back to square one. And if I let the car cool & restart, it usually doesn't come back to 2% by the time it heats up. Could I be getting bad data stored during Learning? I have other reasons to suspect this. After a WOT event, the fuel will often cut off completely for about 10 seconds, after which time it restarts abruptly (a hard light). Very disconcerting on the on-ramp.

  6. #6
    Join Date
    Dec 2009
    Location
    Connecticut
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    Quote Originally Posted by j_reins View Post
    If the IAC is large-ish, blocking the IAC air inlet will cause the car to stall (at idle).
    The engine shouldn't stall when blocking off the IAC air inlet port (at hot idle).

    If I attempt to adjust the idle screw toward 2%, the RPM will run away high, then slowly come back, but it won't come back to desired hot idle.
    That's because opening the idle speed screw activates the IAC Hold Position. A TPS Autoset is required whenever the idle speed screw is adjusted.

    And if I let the car cool & restart, it usually doesn't come back to 2% by the time it heats up.
    The hot idle IAC Position % doesn't happen until after the oil pressure has stabilized to its idle psi.

    After a WOT event, the fuel will often cut off completely for about 10 seconds, after which time it restarts abruptly (a hard light).
    This sounds like the Decel Fuel Cutoff function.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  7. #7
    Join Date
    Nov 2016
    Location
    St Louis
    Posts
    15

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    Is there any way I can adjust the "Decel Fuel Cutoff" with a Sniper EFI? Does this in any way relate to my wandering ever higher IAC?

    This may not be germane, but the coolant temp shown at Tuning->Basic->Closed Loop Learn->Closed Loop shows "not Avail", while the sensor temp CTS is a good number. EFI software issue?

  8. #8

    Default

    Quote Originally Posted by j_reins View Post
    1) I'm using a mechanical + vacuum advance distributor, so I've disabled spark control.
    This is where I would look first. With the EFI not in control of timing, you could have the distributor's advance mechanism fight the IAC's control. Does your timing advance quickly off idle? If the base timing is low, a couple degrees difference can sometimes make a big difference in idle speed.

    With regards to setting the idle RPM speed and the TPS Position %, you need to adjust the throttle screw until the desired IAC Position % is reached, or the TPS reads 2-3%. Once you are in the 2-3% area, the EFI will go into a IAC Hold mode with the IAC, and you will lose control of idle. To correct this turn the engine off, and restart it. The EFI does an auto zero when you start the engine, and you can continue adjusting the throttle screw again.

  9. #9
    Join Date
    Nov 2016
    Location
    St Louis
    Posts
    15

    Default

    Thank you both for your help! My mechanical advance is all in by 2200 RPM. The total advance IS less than optimum. Base = 12°, and base + total mechanical = 27°, vs about 36° desired. I get another 15° from vacuum. For this reason, I was planning on having my distributor recurved. I will now consider computer control too. And thanks for clarifying the throttle screw operation.

  10. #10
    Join Date
    Oct 2016
    Location
    Albuquerque, NM
    Posts
    73

    Default

    Did you ever solve this? I'm getting a similar issue. I too, am using a vacuum/mechanical distributor, but I do have the parts sitting here to have ECU timing control.

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