Wire Shielding EMI or RF Noise?

Bobby Fazio · 08-14-2020, 10:29 AM

I am still having issues with erratic tach signal at high rpm in the data log and I even see it on the tach as well. My data logs have always been very choppy and jagged which makes the ECU do crazy things and even hits rev limiter which I have set very high.

I shielded my trigger wire that goes from ECU to Crane ignition box. I make sure to keep Magnecor wires away from sensor wires. Some distributor power and trigger wires DO pass by the alternator which makes me wonder if that is an issue. I have checked all grounds, made new grounds, use dielectric grease on plugs and boots, not sure what else to do.

I am told it could just be the nature of a dual-sync distributor that gets its crank signal using the hall effect and harmonics involved but I would like to know which other wires may need shielding.

Painter · 08-14-2020, 01:00 PM

I think that I would completely eliminate the alternator first. Belt off, wires off and isolated make run and see what it does. Maybe install extra grounds. Start with one from ignition box chassis to known ground. And do t trust any grounds! Us the “tug test” on every connection ground and hot. Steel wool all terminals and where they connect.

SS3860 · 08-14-2020, 09:01 PM

Electric fans are a good source for interference also. Separate all ignition wiring from fan wires.

Keith 944 · 08-14-2020, 09:12 PM

Try a 10k ohm 1/2 watt resistor in tach wire

CMcAllister · 08-15-2020, 12:03 AM

I keep ignition wiring and "dirty" lines (alternator, fans & motors) separated as far apart as possible. And twist or braid the ignition trigger wires.

All grounds are connected to the ground post of the battery with copper - wires, cables. Don't rely on sheet metal.

Would be interesting to see what happens if the alternator is not functioning on a pass.

FED 387 · 08-15-2020, 12:12 AM

try grounding the head to the block and the block to the frame or body with the old style braided ground straps--NEVER use solid core wire for ground wire --if you do use braided wire make sure it is of sufficient gauge and not only crimped but put a bit of solder on the wire and connecter crimp area to make sure it is really grounded ---

08-14-2020, 10:29 AM	#1
Bobby Fazio VIP Member Join Date: Nov 2009 Location: Egg Harbor Township, NJ Posts: 1,468 Likes: 1,446 Liked 4,365 Times in 501 Posts	Wire Shielding EMI or RF Noise? I am still having issues with erratic tach signal at high rpm in the data log and I even see it on the tach as well. My data logs have always been very choppy and jagged which makes the ECU do crazy things and even hits rev limiter which I have set very high. I shielded my trigger wire that goes from ECU to Crane ignition box. I make sure to keep Magnecor wires away from sensor wires. Some distributor power and trigger wires DO pass by the alternator which makes me wonder if that is an issue. I have checked all grounds, made new grounds, use dielectric grease on plugs and boots, not sure what else to do. I am told it could just be the nature of a dual-sync distributor that gets its crank signal using the hall effect and harmonics involved but I would like to know which other wires may need shielding. __________________ '65 Mustang SS/L & L/SA DriverInterviews.com \| App.DragInsights.com

08-14-2020, 01:00 PM	#2
Painter Member Join Date: Dec 2012 Posts: 227 Likes: 4 Liked 162 Times in 45 Posts	Re: Wire Shielding EMI or RF Noise? I think that I would completely eliminate the alternator first. Belt off, wires off and isolated make run and see what it does. Maybe install extra grounds. Start with one from ignition box chassis to known ground. And do t trust any grounds! Us the “tug test” on every connection ground and hot. Steel wool all terminals and where they connect.

08-14-2020, 09:01 PM	#3
SS3860 Junior Member Join Date: Oct 2019 Posts: 88 Likes: 9 Liked 163 Times in 55 Posts	Re: Wire Shielding EMI or RF Noise? Electric fans are a good source for interference also. Separate all ignition wiring from fan wires.

08-14-2020, 09:12 PM	#4
Keith 944 VIP Member Join Date: Feb 2006 Location: Dela-where? Posts: 2,193 Likes: 1,160 Liked 1,877 Times in 577 Posts	Re: Wire Shielding EMI or RF Noise? Try a 10k ohm 1/2 watt resistor in tach wire __________________ KEITH MAYERS 2-1/2 X somebody Still many X nobody Last edited by Keith 944; 08-15-2020 at 10:40 AM.

08-15-2020, 12:03 AM	#5
CMcAllister Senior Member Join Date: Sep 2006 Location: Fulton County, PA Posts: 614 Likes: 16 Liked 919 Times in 258 Posts	Re: Wire Shielding EMI or RF Noise? I keep ignition wiring and "dirty" lines (alternator, fans & motors) separated as far apart as possible. And twist or braid the ignition trigger wires. All grounds are connected to the ground post of the battery with copper - wires, cables. Don't rely on sheet metal. Would be interesting to see what happens if the alternator is not functioning on a pass.

08-15-2020, 12:12 AM	#6
FED 387 VIP Member Join Date: Jun 2006 Posts: 3,416 Likes: 522 Liked 330 Times in 178 Posts	Re: Wire Shielding EMI or RF Noise? try grounding the head to the block and the block to the frame or body with the old style braided ground straps--NEVER use solid core wire for ground wire --if you do use braided wire make sure it is of sufficient gauge and not only crimped but put a bit of solder on the wire and connecter crimp area to make sure it is really grounded ---