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Thread: Electrical Noise Interference

  1. #1

    Default Electrical Noise Interference

    I have a custom twin electric fan deal, and when it turns on, it pulls a lot of amps. I have it wired from two relays, directly to the junction post on the fuse panel. From there, the voltage sensing wire goes to the alternator, and the main alternator output wire, is also at the fuse panel junction. I wired the ECU directly to the battery, and the ECU controls the fan relay(s) ground.
    The idle dips down from 950 a couple hundred RPMs on initial fan start up, because of the load on the alternator, and makes the engine run a bit rough.
    The idle mixture goes rich and starts to hunt, when the fans are running, but cruising on the road the fan doesn't affect it much.
    The shielded crank reluctor pickup wiring runs within a couple inches of the main alternator output wire, in the harness. Is that close enough to cause interference?
    '66 Beaumont Sport Deluxe - LS2, Terminator, Performer RPM, 227°/231°/110° LSA, long tubes, Extreme Automatics Stage 3 2004R, Edge 3500 stall, Transbrake, 3.50 rear, 100HP dry shot

  2. #2
    Join Date
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    Default

    Quote Originally Posted by 66 Beaumont View Post
    The idle dips down from 950 a couple hundred RPMs on initial fan start up, because of the load on the alternator, and makes the engine run a bit rough.
    I don't think this is caused by electrical noise interference. Many years ago, I used to have a similar problem with my Spal dual electric fans.
    I solved the problem with better overall grounding (Link), heavier gauge fan wiring, a 75 amp relay (Link) and upgrading to a Ford 3G alternator.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, 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.

  3. #3

    Default

    *Update - I loaded the smooth Fuel Graph I made, lowered the CL Compensation Limits from 100% to 15%, and continued with 100% Learn limit. Right away, it runs much nicer, and the fans don't affect the AFR nearly as much. The dip in the idle is compensated with the IAC?
    '66 Beaumont Sport Deluxe - LS2, Terminator, Performer RPM, 227°/231°/110° LSA, long tubes, Extreme Automatics Stage 3 2004R, Edge 3500 stall, Transbrake, 3.50 rear, 100HP dry shot

  4. #4
    Join Date
    Dec 2009
    Location
    Connecticut
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    Quote Originally Posted by 66 Beaumont View Post
    The dip in the idle is compensated with the IAC?
    Yes, provided the throttle blades are properly adjusted.
    Adjust the idle speed screw on throttle body, to achieve an IAC Position of about 5% at hot idle.
    Remember to perform another TPS Autoset, whenever you adjust the idle speed screw on the throttle body.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, 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.

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