Factory gauges reading high - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Kcorey · 02-24-2019, 10:02 AM

Hey guys I’ve got a 72 cheyenne super k20. I just put a rebuilt sbc 350 ( truck originally came with a 350/th350/np205) in it . It has a factory tachometer in the dash. I installed a MSD ready to run distributor with separate coil. The tachometer is reading around 6-700 rpm higher then the engine is actually turning when I am cruising ( verified with timing light ). Also my engine temperature is almost pinned in the hot and the engine is at 180* verified with thermal imager . Any thoughts on how to correct the factory gauges ?

davepl · 02-24-2019, 12:06 PM

Is the MSD a multispark unit? Are you picking up your tach signal on a special TACH line or from the coil?

Because if you connect a tach to the coil of a multispark (that's the M in MSD) ignition, it's going to see the extra pulses as increased RPM.

This is the problem I have with my Ignitor III module. But usually distributors have a TACH signal line that knows to just fire once per hole, and that solves it.

Kcorey · 02-24-2019, 03:36 PM

I connected tach signal to the separate grey wire from the msd distributor that is labeled for tachometer .

**HO455** · 02-24-2019, 05:14 PM

Subscribed as I have the same problem. I've been hoping that my V-8 tach housing doesn't have I-6 guts in it.

02-24-2019, 10:02 AM	#1
Kcorey Registered User Join Date: Jan 2018 Location: Madison CT Posts: 64	Factory gauges reading high Hey guys I’ve got a 72 cheyenne super k20. I just put a rebuilt sbc 350 ( truck originally came with a 350/th350/np205) in it . It has a factory tachometer in the dash. I installed a MSD ready to run distributor with separate coil. The tachometer is reading around 6-700 rpm higher then the engine is actually turning when I am cruising ( verified with timing light ). Also my engine temperature is almost pinned in the hot and the engine is at 180* verified with thermal imager . Any thoughts on how to correct the factory gauges ? __________________ 1970 Chevy c10 SWB twin turbo LS3. 1972 Chevy k20 super cheyenne.

02-24-2019, 12:06 PM	#2
davepl Registered User Join Date: Aug 2006 Location: Redmond, WA Posts: 6,332	Re: Factory gauges reading high Is the MSD a multispark unit? Are you picking up your tach signal on a special TACH line or from the coil? Because if you connect a tach to the coil of a multispark (that's the M in MSD) ignition, it's going to see the extra pulses as increased RPM. This is the problem I have with my Ignitor III module. But usually distributors have a TACH signal line that knows to just fire once per hole, and that solves it. __________________ 1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible

02-24-2019, 03:36 PM	#3
Kcorey Registered User Join Date: Jan 2018 Location: Madison CT Posts: 64	Re: Factory gauges reading high I connected tach signal to the separate grey wire from the msd distributor that is labeled for tachometer . __________________ 1970 Chevy c10 SWB twin turbo LS3. 1972 Chevy k20 super cheyenne.

02-24-2019, 05:14 PM	#4
HO455 Post Whore Join Date: Feb 2016 Location: Portland Oregon Posts: 10,884	Re: Factory gauges reading high Subscribed as I have the same problem. I've been hoping that my V-8 tach housing doesn't have I-6 guts in it. __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.