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Thread: Losing tach signal when engine gets up to temp?

  1. #11


    I suppose a visual aid will clear up anything I may have done wrong. The relay on the left is my source for 12V switched power with KOEO and during cranking. It's triggered by a wire running from the factory ignition switch. It supplies what I thought would be clean switched 12V to the busbar with the three pink wires (Sniper EFI, Dual Sync Distributor, Coil Driver Module) and also the two orange wires, which supply 12V switched power to the two fan relays on the right. The fan relays are ground triggered by the Sniper EFI. I assumed that since it was only supplying power to turn the relay on and not directly powering the fans that it would be considered clean. If it's possible it's not clean power, then I'll look into changing it up. I assume that removing the two fan 12V switched wires off the bus onto their own switched 12V would be the way to go. I just need to figure out how to get another switched 12V to there. Thanks again.
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  2. #12


    The bus supplying voltage to the relays as you describe should be fine. My bigger concern is what happens to your main voltage circuit - voltage & noise when the fans come on.

  3. #13
    Join Date
    Nov 2014
    Ont. Canada


    Is that chassis ground just for the relays?

  4. #14


    Stop worrying about the final solution and go into troubleshooting mode instead. Disconnect the alternator and see what happens when the engine warms up. Disconnect the fans and see what happens when the engine gets warm. Just go around the engine and disconnect everything you can. Once you find the problem figure out how to deal with it.

  5. #15


    Quote Originally Posted by 81 TransAm View Post
    Is that chassis ground just for the relays?
    The ground you see is for the relay on the left (supplies switched 12V triggered by ignition switch) and also the coil driver module ground (driver module is mounted above the busbar). The 3rd wire on that ground just runs to another ground point on the sway bar mount where the 2 cooling fan relays are grounded. I'll attach pics.
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    Last edited by streetking408ys; 10-20-2019 at 06:19 PM.

  6. #16


    That looks like the fans, the coil driver and the Sniper are getting power from a common busbar, which is a bad idea in my opinion, no disrespect to other opinions. Holley is very clear not to have a dirty source like the coil be the feed for the Sniper. True you aren't feeding the Sniper with it, but if they are all on a common busbar it is the same thing. Noise can get into the busbar and travel to the Sniper.

    Like Andy said start testing. Rig up some temporary wiring with the Sniper on a stand-alone relay that gets power directly from the battery to test and see what happens. Or change the fan temps to 100°F and see if it dies at a lower temp.

    Or better yet, look at your datalog. You can see when the fans come on and if it's the same time the car dies. It will show you EMI as well. You have everything you need to troubleshoot it.
    69 Camaro
    400 SBC, ProCharger D1SC

  7. #17


    I’ll start it up and play with it tomorrow and report back. On a positive note I find the car runs really well especially considering zero tuning. I took it to the stop sign and back (1/4 mile each way). The cam that's in there only pulls 75 kPa. I’m thinking idle of 850 or 900 seems okay. Manual transmission.

    After coming across posts talking about CTS & MAT not agreeing on a cold engine, I went out this morning on a bone cold engine, sitting overnight in my shop. Shop thermostat shows 51°F, infrared thermometer shot of the intake manifold (where the CTS is located) shows 51°F, Sniper MAT shows 54°F, CTS shows 70°F. Looks like I need to replace the CTS. Hope I can find a TX3 locally today.
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  8. #18
    Join Date
    Dec 2009


    Quote Originally Posted by streetking408ys View Post
    Looks like I need to replace the CTS. Hope I can find a TX3 locally today.
    Yep, you're on the right track.

    Originally Posted by Danny Cabral
    Sniper EFI Replacement Sensors - Auto Parts Store
    CTS Sensor: Standard Motor Products TX3
    TPS Sensor: Standard Motor Products TH191
    IAC Motor: Standard Motor Products AC416
    WBO2 Sensor: Bosch 17025, 0258017025 (LINK/LINK/LINK/LINK)
    (The Sniper EFI 2 bar MAP sensor is internal with the ECU. The Sniper
    EFI IAT sensor is a circuit board sensor that measures one throttle bore.)
    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.

  9. #19


    Yeah, you want your CTS to work correctly, but that probably isn't your problem. If the CTS isn't reading correctly it will cause other problems such as turning off the choke (enrichment) either too soon or not soon enough. I had a customer who was always running enrichment since his CTS was reading way too cool. He couldn't figure out why enrichment was always on. The temp gauge in his dash said the engine was up to temp, but when we looked at the datalogs the Sniper thought it was cold.

  10. #20


    Thanks very much for that, and I fully realized that. I just want everything correct before I start getting into tuning/troubleshooting.

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