Wire Shielding EMI or RF Noise?

[Painter]

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]

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

[Keith 944]

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

[CMcAllister]

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]

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 ---

[Painter]

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”!

[Tom Goldman]

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.

[Jackie McCracken]

Originally Posted by FED 387

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 ---

nothing wrong with solid wire and electrically it's actually better if done right. however, having said that stranded wire will not usually break because of vibration which solid wire will do, like a paper clip bent back and forth it will break at some point.


Some friends that run a sprint car had a similar goofy problem, make sure the distributor body is also properly grounded as the gasket will act as an insulator. You cannot have too many grounds, the more the better, including block, heads, intake, AND distributor.. and use the biggest wire you can physically get away with as modern ignitions pull a **** load of current. 12ga or bigger!


Jackie

[west coast]

So I have had the same problem as Bobby, my data logs for the rpm is very squiggly. I tried almost every thing listed so far and gave up a couple of years ago on this. One thing that I did do was go back to my tach which is a 2 channel with drive line sensor, down loaded it and my logs looked clean on RPM. one thing that was mention by Tom I am going to try. if anybody gets there's fix please post how you did it.