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Thread: HP EFI Questions on IAC & Water/Meth Kit

  1. #1

    Lightbulb HP EFI Questions on IAC & Water/Meth Kit

    Just hoping to get some opinions & advice on a few things. Hoping Danny will chime in as he's been super helpful in the past.
    Got a Fox body Mustang, 331 engine with a Vortech supercharger. Running HP EFI (Universal Kit), system is a few years old.

    First questions is: Running a GM style IAC, the HP EFI Universal Kit has a 3 or 4-pin flat plug for the IAC I believe. Bought a new IAC from Holley, cut the universal kit IAC plug off, soldered in the GM style IAC per the wiring diagram that came with it from Holley. Confirmed that wiring with several tech articles on these forums, so everything is good, car runs good, idles good, IAC is doing it's job, etc. Problem is, when the car is off, key out and I'm working in the engine bay, I can hear clicking and what sounds like the IAC motor running? Doesn't do it all the time, but I've noticed it several times while working on the engine? When I disconnect the IAC plug, noises stop, so I know it's the IAC. I'll answer a few things below:

    1. The red/white ECU trigger wire is tied to the correct power source per the Holley instructions, checked several times, and car has been running for over three years with this system.
    2. Have an Optima Red Top, top post & side post. I run the HP EFI Red & Black battery lead wires directly to the side posts, nothing else is on those posts except the Holley system. All the car's wiring still utilizes the top post like it came from the factory.
    3. Car sits mostly, so I generally disconnect the ground side terminal of the top post. Holley wires generally never get disconnected from the side posts. IAC still makes noise with the car's main wiring disconnected. I understand the ECU is still being fed from the side posts, but I shouldn't have to disconnect the battery to fix this issue.

    Any thoughts on this? My second question is, I just purchased Holley's Water/Meth kit, kit is not here yet, just got sick of running race gas.
    My question is, where is the best place to run the 1000cc nozzle in my mondo blower discharge tube? I've talked to Holley tech twice in a few month span, one guy said close to the throttle body inlet, another said it has to be installed by the blower head unit volute outlet? Those two locations are complete opposites, so looking for any advice. The discharge tube curves towards the throttle body around the strut tower, would be a good place to plum the nozzle in, but worried some of the meth mist will make it's way into the blow off valve which is directly below that curve? Any advice would be appreciated. Thanks guys.

  2. #2


    Nobody has any advice on the IAC or the Meth Nozzle?

  3. #3


    Today is track day. I'll post a response later. Having too much fun.

  4. #4


    I was told by Rodney at ProMeth, to mount the nozzle as far away from the TB as I could. For your combo, I'd spray before the blower. Currently, I have two nozzles after my intercooler, considering adding one at the turbo inlet.
    '95 Lightning, HP EFI, 351W, S472SX-E,20PSI,pump and W/M

  5. #5
    Join Date
    Dec 2009

    Default (General IAC Information - Read "IAC NOTES" & "IAC Motor Harness Connector PIN-OUTS")
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  6. #6


    Quote Originally Posted by Danny Cabral View Post (General IAC Information - Read "IAC NOTES" & "IAC Motor Harness Connector PIN-OUTS")
    Read the entire thread and ensured my tune and the IAC was spot-on to this thread.
    Four IAC wires at the ECU P1B connector (same for all 4-wire IAC stepper motors):
    Pin B1 - purple/blue - "A LO" - goes to Pin B (Gray) wire on IAC connector
    Pin B2 - purple/yellow - "A HI" - goes to Pin A (Black) wire on IAC connector
    Pin B8 - purple/white - "B LO" - goes to Pin D (Purple) wire on IAC connector
    Pin B9 - purple/black - "B HI" - goes to Pin C (White) wire on IAC connector

    I pulled apart the IAC harness at the connector and the ECU connector and everything is as posted above.
    I called Holley tech, I'm using the GM thread-in style IAC (part #543-2). They told me this IAC shouldn't really be used with the HP EFI? They have sold me two of them in the past and this never came up. The IAC in the car only has 100 miles on it.

    Any advice where to look now for why the IAC is running on occasion when the car is off and key is out? Checked the ground and power leads, both are per the Holley instructions.

    Car seems to be running fine, but my friend is helping me tune it and says he doesn't think the IAC is functioning properly based on starting, especially hot and some idle characteristics. A fresh set of ideas would be appreciated.

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