Need quick answer on IAC question
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Joined: Jul 2002
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From: Toledo, OH
Car: '87 Formula
Engine: 350
Transmission: Auto
Need quick answer on IAC question
Ok, heres the rundown. I just got this new setup running, pretty tickled. I start it up and, after getting the timing in the neighborhood, its idling at around 2000. It's running way rich (blms at 108 pretty quickly) and may need some timing into the chip (header collectors glowing bright orange). What I need to do is get the idle down to normal. After logging about a minute's worth of data, I scroll through and see that as soon as the engine fires, the IAC goes from 160 steps down to zero in a matter of maybe a second or two while the rpms go from 900 to 1900 in the same time period. Desired idle speed is 662rpm. My question is, did I wire in the IAC backwards? Looking at the IAC schematics, it seems that if you had every pin (A B C D) wired in reverse it would spin the IAC pintle backwards. So, by setting the IAC at 160 steps initially (computer default for start-up) which should be fully opened, it's probly fully closed, and by trying to bring the idle down it instead brings it up but has no way of dealing with it otherwise. Can someone verify my assumptions, I have limited time to piddle when I make it home to work on the car on weekends, I'm just trying to maximize my efficiency at fixing bugs.
TIA
Ben
edit: I emailed someone on this board that builds harnesses for the RamJet and he pretty much verified that I do have them backwards. Problem solved.
TIA
Ben
edit: I emailed someone on this board that builds harnesses for the RamJet and he pretty much verified that I do have them backwards. Problem solved.
Last edited by 87Formula4bbl; Mar 7, 2005 at 12:28 PM.
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From: Corona
Car: 92 Form, 91 Z28, 89 GTA, 86 Z28
Engine: BP383 vortech, BP383, 5.7 TPI, LG4
Transmission: 4L60e, 700R4, 700R4..
Axle/Gears: 3.27, 2.73
there are 2 coils inside of the IAC, and switching the wires on one of them will reverse the direction of travel. Swapping A and B should be good enough if you want to try that theory.
You may have a stuck open throttle. You may have a huge air leak (runners on the wrong sides). Maybe a dead IAC, or stuck IAC, with the extra fuel bogging it at first, and closed loop leaning it back to normal causing the idle to rise.
Do you have to depress the pedal to get it to start? I think you may be right on this one, though. I've seen many IAC diagrams that have the pins in different orders, so I can imagine it being backwards easily.
You may have a stuck open throttle. You may have a huge air leak (runners on the wrong sides). Maybe a dead IAC, or stuck IAC, with the extra fuel bogging it at first, and closed loop leaning it back to normal causing the idle to rise.
Do you have to depress the pedal to get it to start? I think you may be right on this one, though. I've seen many IAC diagrams that have the pins in different orders, so I can imagine it being backwards easily.
Thread Starter
Senior Member
Joined: Jul 2002
Posts: 815
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From: Toledo, OH
Car: '87 Formula
Engine: 350
Transmission: Auto
Well, its a brand new setup. New everything, IAC, etc. So I don't think anything is stuck. I think the wires are probably backwards. Just looking at the datalog, it seems that it is doing exactly the opposite of what it's supposed to. Having two coils, it seems that it would send current through either one for stepping the pintle in and the other to step it out, does that sound right. So ya, sending current through the opposite coils it was intended to, it would work in reverse. Just trying to think this through in my mind, does it sound right? Heres a snippet of the log:
Code:
TPS RPM MAP Runtime Target A/F INT BLM Cell BPW Desired RPM IAC Steps SA(TDC) 0.57 0 80.39 0 14.73 125 108 4 0.5 3187 160 84.38 0.57 0 70.59 0 13.24 125 108 4 0.5 3187 160 83.67 0.57 900 60.39 0 13.57 128 118 4 0.21 662 152 89.3 0.57 950 56.86 0 13.6 128 118 4 0.24 662 136 89.3 0.57 1075 53.73 0 13.6 128 118 4 0.26 662 120 89.3 0.57 1200 49.8 0 13.8 128 118 4 0.27 662 103 89.3 0.57 1325 46.67 0 13.91 128 118 4 0.28 662 88 89.3 0.57 1425 43.14 0 14 128 118 4 0.3 662 84 89.3 0.57 1500 40.39 1 14.06 128 118 4 0.33 662 84 84.02 0.57 1575 38.43 1 14.12 128 118 4 0.34 662 82 84.02 0.57 1625 36.47 1 14.19 128 118 4 0.36 662 80 84.02 0.57 1675 35.29 1 14.28 128 118 4 0.37 662 79 84.02 0.57 1725 34.12 1 14.34 128 118 4 0.39 662 78 84.02 0.57 1725 33.73 1 14.4 128 118 4 0.39 662 77 84.02 0.57 1775 32.94 1 14.44 128 118 4 0.4 662 73 84.02 0.57 1750 32.94 1 14.44 128 118 4 0.4 662 68 84.02 0.57 1775 32.55 1 14.44 128 118 4 0.41 662 61 84.02 0.57 1775 32.94 1 14.44 128 118 4 0.41 662 49 84.02 0.57 1775 32.94 2 14.44 128 118 4 0.4 662 37 84.02 0.57 1800 32.94 2 14.44 128 118 4 0.4 662 25 84.02 0.57 1800 33.33 2 14.44 128 118 4 0.4 662 13 84.02 0.57 1825 32.94 2 14.44 128 118 4 0.4 662 2 84.02 0.57 1825 32.94 2 14.44 128 118 4 0.4 662 0 84.02 0.57 1825 32.55 2 14.44 128 118 4 0.41 662 0 84.02
Last edited by RBob; Mar 7, 2005 at 02:31 PM.
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Joined: Jul 2002
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From: Toledo, OH
Car: '87 Formula
Engine: 350
Transmission: Auto
Sorry for the messy table, I tried reformatting it but doesnt seem like it helped any.
Last edited by 87Formula4bbl; Mar 7, 2005 at 12:28 PM.
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From: Chasing Electrons
Car: check
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Originally posted by 87Formula4bbl
Sorry for the messy table, I tried reformatting it but doesnt seem like it helped any.
Sorry for the messy table, I tried reformatting it but doesnt seem like it helped any.
A coil can be found by measuring the resistance between the pins. A coil will measure about 40 ohms. Just two coils and only need to swap the wires on one.
RBob.
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