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

  1. #1

    Default Losing tach signal when engine gets up to temp?

    New installation. I'm putting together a '69 Mustang with a 428. Using Sniper, Dual Sync distributor, coil driver module. I did the 1st start yesterday, it fired up immediately and ran acceptably. The problem is after it had gotten up to temp, where my electric fans came on/off a few times I could not get the car to restart. There's was no RPM shown on the display. It was a long day so I decided to hang it up for the night and start fresh in the morning. This morning it fired right up. Stopped and started the engine several times, no problem. Then at one point the engine just cut out & died, the display remained powered up the whole time. I tried starting it and it fired right up. After several minutes of running it some more and then turning the engine off I tried restarting the engine and it would not start, again no RPM on the display. Seems to me the pattern is once the engine is hot, I lose tach signal. Any ideas? Thanks.

  2. #2
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    23,057

    Default

    The RPM signal is derived from the Holley EFI Dual Sync Distributor, so check that wiring first.
    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

    That sounds very much like EMI as well. My initial startup was similar, but mine would start cutting out after a couple of minutes. I had to regroup on the wiring. Sniper +12V switched power should be on a relay for clean battery power. Check your battery grounds as well. A ground from the battery to the engine is a must. You also need one from battery to chassis and a third from chassis to engine. If it'll run long enough to grab a datalog, please post it along with your Config File.
    69 Camaro
    400 SBC, ProCharger D1SC

  4. #4
    Join Date
    Oct 2017
    Location
    Los Angeles
    Posts
    399

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    A quick look at a datalog will tell you if you have EMI. You can watch this video to learn if you have EMI: https://youtu.be/r8MzMY4Uwi8
    1964 Chevy Nova, 383 Stroker, AFR 210 Heads, Ford 9inch w/TrueTrac/3.90 Gears, Powerglide Transmission. www.SoCalStreetCars.com

  5. #5

    Default

    There's a guy over on camaros.net with the same problem. Starts & runs fine cold, but as soon as it warms up, it quits without an RPM signal. Tried multiple distributors, wiring, etc. Ended up being the Sniper ECU itself if I remember correctly.

  6. #6

    Default

    Thanks for the help guys. I've been working on other parts of the car. I've gotten to the point where most of the car is ready so I need to get this going. I actually took the car out for its 1st drive today. Just went about a mile down the road, car doesn't have a coolant overflow bottle so it was puking a little coolant so I turned around. Thankfully I did, cause when I got back same thing happened losing tach signal (no RPM on display). I feel I was pretty good about how I ran the wires. I currently have a relay that supplies clean 12V to a busbar. The busbar feeds 2 cooling fan relays for switched 12V, Holley Sniper, the dual sync distributor and the Sniper coil driver module. I made new 2 AWG positive battery cable to starter solenoid, 2 AWG ground from battery to engine block, 2 AWG from block to frame, also a 1-wire alternator grounded with 4 AWG to frame, and 12 AWG ground to body. The Sniper coil driver module is grounded to body and a redundant ground runs from that ground point to another spot on the frame (sway bar bushing bracket) I've had the problem occur often enough that I'm confident it's temperature related. I also find for a completely untuned system, it runs quite well. Hope I'm posting this datalog correctly, 1st time. So this datalog was with engine already up to temp and quit on me. Once it cooled a bit and ignition came back I ran this datalog for a few minutes until the ignition quit again (when it got warm enough). Seems like when it's about to cut out, the ignition timing starts to bounce quite a bit then I lose tach signal until it cools a bit. I was feeling like I have a bad dual sync distributor where temp messes with something in there. No idea.
    Here's the datalog: https://www.dropbox.com/s/ciyabwzaro...r_0002.dl?dl=0
    This is a quick video I took of the car today: https://youtu.be/a3ZmawZ-65A
    Last edited by streetking408ys; 10-19-2019 at 09:09 PM.

  7. #7

    Default

    It seems like there's some correlation with your fans turning on from your first post. Are you controlling the fans with the Sniper or a temperature sensor? What alternator are you running? If it's a 1G you may be getting noise from the alternator under increased load from the fans. Or, there may be a significant voltage drop when the fans kick on. The 3G alternators produce much cleaner power for less CPU interference. Also, the 130 amp version is less likely to experience a large voltage drop. Do you have then Sniper on a spacer? If not, it may be getting heat soaked. Or a slightly taller spacer my help reduce heat.

  8. #8

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    Definitely get the Sniper 12V trigger off of the same power source as the fans. Fans are pretty “dirty” electrically and with a shared connection with the Sniper it's probably backfeeding. The Sniper is so sensitive, so you need to isolate it. You can share the power with the distributor and the CD box, but I wouldn’t share with the fans.
    Last edited by gregs69rs; 10-20-2019 at 11:34 AM.
    69 Camaro
    400 SBC, ProCharger D1SC

  9. #9

    Default

    Okay thanks for that. Just to be clear, the +12V switched shared power source for the two Fans, Sniper EFI, Dual Sync Distributor, Coil Driver Module is only to feed switched +12V to the fan relays; that source does not directly feed the fans. The fans are powered directly from the battery through the relay. Don't know if that changes anything.

  10. #10

    Default

    Not sure I'm completely clear as I thought the power came from a busbar that fed both the Sniper relay and the fan relay. But I would isolate the Sniper 12V relay like this: Relay trigger side - input from your switched source, output ground. The power side - feed should come directly from the battery and the output side should be the pink 12V trigger wire. You could put the distributor on the output side as well, but the more isolated the Sniper is, the better.
    69 Camaro
    400 SBC, ProCharger D1SC

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