Tach at 3,000 rpm at idle - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**68ls1** · 08-23-2021, 02:24 AM

We have just installed a Holley Terminator EFI set up with Holley Hyperspark distributor, ignition coil and CD ignition box on SBC in my C10. The tach (5,000 rpm add on restoration one in dash) is now showing 3,000 rpm when idling, read out on Holley display is correct.

Anyone encountered this problem? Where to look?

thanks

**The Rocknrod** · 08-23-2021, 08:44 AM

I'm assuming this is your system? On your Tach, who makes it? Do you have a link?

**68ls1** · 08-23-2021, 08:59 AM

Quote:

Originally Posted by The Rocknrod

I'm assuming this is your system? On your Tach, who makes it? Do you have a link?

Yes, that looks like the system.

I believe this is the tach, was in truck when I purchased, https://www.brotherstrucks.com/1967-...tinfo/TACH772/

Custom 68 · 08-23-2021, 02:51 PM

I'm sure this is different but when I did my ls swap I used the GM factory computer and my aftermarket tack had to be switched to 4cyl mode to read correct. This may be apples to oranges but figured I would throw it in.
Dave

**biketopia** · 08-25-2021, 10:57 AM

Big difference in terminator or the sniper system, terminator has an external ECM, sniper it's all internal to the throttle body, which do you have? I have a sniper system with the hyper spark distributor, a 6al box, and blaster ss coil on my camaro that I'm tinkering with until I swap it all into my c-10. My autometer tach and handheld read identical, the tach needs to be hooked to the brown wire on the sniper. If you have terminator set up that may change.

https://www.efisystempro.com/efi-pro...gnition-wiring

**68ls1** · 08-25-2021, 05:22 PM

Quote:

Originally Posted by biketopia

Big difference in terminator or the sniper system, terminator has an external ECM, sniper it's all internal to the throttle body, which do you have? I have a sniper system with the hyper spark distributor, a 6al box, and blaster ss coil on my camaro that I'm tinkering with until I swap it all into my c-10. My autometer tach and handheld read identical, the tach needs to be hooked to the brown wire on the sniper. If you have terminator set up that may change.

https://www.efisystempro.com/efi-pro...gnition-wiring

I am running a Terminator X Max Stealth
https://www.holley.com/products/fuel...parts/550-1013

We tried swapping wires, adding diodes etc without any luck.
On advice from gauge specialist we have pulled tacho, and sent to him. He advises there are two kinds of signals, a coarse signal and a fine signal which the Holley supplies. We will see how it goes.

In better news my temp gauge which would not come off low is now reading more accurately?

**biketopia** · 08-26-2021, 08:04 AM

Ahh ok, the terminator is nice ECU set up. It should do what ever you need it to. There are tons of settings in the input output sections was there maybe something you needed to adjust using the laptop software not the handheld.

08-23-2021, 02:24 AM	#1
68ls1 Senior Member Join Date: Jan 2008 Location: Melbourne, Victoria, Australia Posts: 216	Tach at 3,000 rpm at idle We have just installed a Holley Terminator EFI set up with Holley Hyperspark distributor, ignition coil and CD ignition box on SBC in my C10. The tach (5,000 rpm add on restoration one in dash) is now showing 3,000 rpm when idling, read out on Holley display is correct. Anyone encountered this problem? Where to look? thanks

08-23-2021, 08:44 AM	#2
The Rocknrod Moderator Join Date: Aug 2011 Location: China Spring, TX Posts: 7,280	Re: Tach at 3,000 rpm at idle I'm assuming this is your system? On your Tach, who makes it? Do you have a link? Attached Images __________________ Master Chief, US Navy, Retired 1964 C10 Step-side Short Bed - In Progress 2009 2500HD Duramax LTZ 1948 GMC Panel 1956 Big Window Stepside 1953 5 Window Chevy Stepside 1932 Coupe New Seat Foam for Bench Seats? Last edited by The Rocknrod; 08-23-2021 at 08:50 AM.

08-23-2021, 02:51 PM	#4
Custom 68 Registered User Join Date: Nov 2001 Location: Springfield, MO Posts: 2,930	Re: Tach at 3,000 rpm at idle I'm sure this is different but when I did my ls swap I used the GM factory computer and my aftermarket tack had to be switched to 4cyl mode to read correct. This may be apples to oranges but figured I would throw it in. Dave __________________ Dave 1968 Custom Chevy with turbo charged 5.3 gen III 4l80e swap 1967-71 GMC 3/4 ton long step 4x4 (not sure what year exactly?) "A good friend will bail you out of jail...but a true friend will be sitting next to you saying "that was frekin awesome". "If it doesn't fit force it...If it breaks then it needed to be replaced anyway!"

08-25-2021, 10:57 AM	#5
biketopia Senior Member Join Date: Jul 2015 Location: Warrenton VA Posts: 1,008	Re: Tach at 3,000 rpm at idle Big difference in terminator or the sniper system, terminator has an external ECM, sniper it's all internal to the throttle body, which do you have? I have a sniper system with the hyper spark distributor, a 6al box, and blaster ss coil on my camaro that I'm tinkering with until I swap it all into my c-10. My autometer tach and handheld read identical, the tach needs to be hooked to the brown wire on the sniper. If you have terminator set up that may change. https://www.efisystempro.com/efi-pro...gnition-wiring __________________ 71 c-10 Long Bed, under the knife for a No Limit Engineering Wide Ride Chassis Pack and coil over static drop. 07 Silverado Classic 2wd 95 Camaro 427SBC/TH350

08-26-2021, 08:04 AM	#7
biketopia Senior Member Join Date: Jul 2015 Location: Warrenton VA Posts: 1,008	Re: Tach at 3,000 rpm at idle Ahh ok, the terminator is nice ECU set up. It should do what ever you need it to. There are tons of settings in the input output sections was there maybe something you needed to adjust using the laptop software not the handheld. __________________ 71 c-10 Long Bed, under the knife for a No Limit Engineering Wide Ride Chassis Pack and coil over static drop. 07 Silverado Classic 2wd 95 Camaro 427SBC/TH350

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