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.

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.

Re: Wire Shielding EMI or RF Noise?
 

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

Re: Wire Shielding EMI or RF Noise?
 

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

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.

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 ---

Re: Wire Shielding EMI or RF Noise?
 

Solder is often confused as the very best in connections, when in fact poorly solder connections are very bad. If you don’t know how and have good equipment then stick with good crimps and vigorously apply the “tug test”!

Re: Wire Shielding EMI or RF Noise?
 

Too many devices on a common ground can lead to r/f noise .
As was mentioned the fan is the single dirtiest source on the car followed by the electric fuel pump.
I use ferrite core shields on everything .
I use the type with a plastic case that snaps together around the wire . Very inexpensive, available on Amazon ,EBay .
The old school and still one of the best ways to find the source is to use an old cheap AM pocket radio tuned down to lowest end of the band ,around 540 . it will pick the culpret just about every time.

Re: Wire Shielding EMI or RF Noise?
 

Tom where do you put them? On the plug wires, signal carrying wires, 12v or ground wires?

Re: Wire Shielding EMI or RF Noise?
 

Bobby, you place them on the supply b+ wire , you can also place them over twisted pairs from the ignition triggers and the coil primary