Shielding The Blue Tach Wire
Seems the blue tach wire is very vulnerable to electronic noise or RF noise, which interferes with the tach signal and it can cause an over rich condition. I had this problem and being an electronics guy that fixes CT scanners I decided to find an easy solution.
I went to my local electronics store and bought 6' of braided RF shielding. I then soldered a ground wire on to the shielding that was later attached to the chassis. Once that was done I pulled the blue wire out of the FiTech harness and installed the shielding. Put the wire back in the harness and ran it through my firewall along with every other wire in my engine compartment. My ignition box (mallory highfire 6al) is under my dash. Once all my wires where ran I connected the blue tach wire to my yellow tach wire from the box and grounded the shielding with the ground wire i installed earlier. I also installed a couple of emi rf clamps. Using my Fluke 1503 ground tester I got a reading of 0.73 ohms resistance between the negitive battery post and any point on my shielding.
This takes about 15 min to do and will almost guarantee you dont get noise on the tach wire. The shielding cost less then a $1 a foot and the clamps probably arent needed but i had them laying around. Every system may not need this but its cheap insurance IMO
Uploaded files:
- You need to login to have access to uploads.
That's great information. I see guys all the time fighting this and the suggestions are all over the place. Will be using this post a lot.
There is one other solution. Use timing control and the Fitech gets signal from the Magnetic pickup. I have never had a problem with this setup.
What electronics shop sells that ? None i have seen and for items online about 5 x that price...
Thanks in advance
Hi Doug,
thanks for post, I found it on EBAY in the end. Best option for cost and delivery being in Australia. Far more expensive than your suggestion thou.
Rob
Amazon Prime to the rescue!
http://amazon.com/gp/product/B01BIBQESG/ref=od_aui_detailpages00?ie=UTF8&psc=1
I am having this issue too. Fitech support said I could shield the blue wire with reflective tape or heat shield product. I had some DEI sleeve for fuel line so I’m going to try that. We’ll see if that works.
To shield from electric fields such as rotor and spark arcs, and from brush-type generator sparks use shielding. The tighter the braided weave the better this shielding will work. Ground on one end only. Grounding on both ends can create ground loops that induce electrical noise into the wire by currents that will flow from small voltage differences between the two ground points.
If you're on a budget, or need a quick fix you can even use household tin foil; it doesn't need to be thick but it does need to be continuous (no gaps) or made with overlapping wraps. Wrap a wire several turns on top of the foil at one end to make a good connection for a ground (most convenient on the motor side) . Then a thin wrap of electrical tape the entire length to hold it together.
Lastly, if you're near high current (e.g. alternator output), be sure to avoid loops. High current creates magnetic fields that will induce currents in looped wires.
Thanks. The DEI didn't work. From what you are saying I can see why. It isn't grounded, just covers the wire. I guess I'll order some of the braided shielding in the posts above and ground as you said.
A little more info. After the install I had run a couple of times in the garage getting the IAC set etc. Ran fine. Then when I took it out on the road to reset kickdown cable and line pressure, it started with this code.
An additional question. I've been focused on shielding the blue wire from the coil to the plug in the harness. Do I also need to shield from the plug to the Fitech unit? This would be separate, so separate grounds?
This seems to be common and a critical issue. I cannot understand why Fitech and Holley would not just send their kits with shielded wire.
The grounded body of the Fitech unit (grounded through the intake manifold) doesn't need any additional grounds, except power connections of course. Don't run wires alongside (in parallel) of spark plug wires, energy from plug wires will capacitively couple into unshielded wires. If wires and plug wires need to cross, keep the crossing area as short as possible (perpendicular is best). All of this will help reduce electrical noise on wires.