Tfi Question

nothwoods · May 21, 2014

I'm relocating my TFI to the fender, using a setup from a mid 90's F-series. I have the distributor and the piece of harness that plugs into the stator. My question is about the shielded wiring involved. Is it just there to prevent radio noise, or does it prevent interference with the PIP signal back to the PCM? I don't have a stereo in my car, and if that's the only issue I can just spice into the harness to extend it, but if it's going to cause any other problems I'll have to figure out how to properly shield the new section of wire.

jrichker · May 21, 2014

Think about how much high voltage radiates from the spark plug wires, and you will realize that the shielding isn't just to prevent noise in your radio or stereo.

Simply put, shield the wire and you can be sure that it isn't a problem.
Shielded multi conductor wire - see
https://www.google.com/#q=18+gauge+3+conductor+shielded+wire.
OR
https://www.google.com/#q=3+conductor+shielded+cable&revid=1629338622

You want at least 3 conductor,18 gauge wire and a 105 C temp rating. With wire gauge, the smaller the number, the larger the copper conductor.

RacEoHolic330 · May 21, 2014

McCully racing can make you a shielded cable if you won't want to spend the effort making your own. They specialize in making TFI relocation kits. I just made a shielded cable for my cam and crank sensor wiring, and it is quite time consuming. I bought copper shielding tape on eBay to make it.

rbohm · May 21, 2014

you can buy shielded cable from a variety of sources. as i recall there are only three conductors needed.

nothwoods · May 21, 2014

Thanks for the replies. A friend of mine does a lot of electronics and computer work, he's looking to see if he has some shielded wire I can use. Seems like the shielding would be easy enough to make, I'm just not sure how to go about grounding it properly. Ill splice in at the center of the firewall where the TFI harness comes off, and the stator harness already has the shielding. Ill need to shield it from there to the TFI.

RacEoHolic330 · May 21, 2014

The issue I had was finding a shielded cable that had a high enough heat rating. Most computer wiring is only good up to 70*C. The lack of affordable results is what prompted me to make my own.

You only need to ground one end of the bare drain wire in the harness. It's usually easier to ground it to wherever you're mounting your heatsink.

rbohm · May 22, 2014

nothwoods said:
Thanks for the replies. A friend of mine does a lot of electronics and computer work, he's looking to see if he has some shielded wire I can use. Seems like the shielding would be easy enough to make, I'm just not sure how to go about grounding it properly. Ill splice in at the center of the firewall where the TFI harness comes off, and the stator harness already has the shielding. Ill need to shield it from there to the TFI.

make sure that any shielded cable you buy from a computer store can handle the electrical load as well as the under hood heat. remember that computer cable doesnt have to handle a lot of power.

Blown88GT · May 22, 2014

I made a shielded & grounded cable from a junkyard Ford one. Did it exactly like I designed 100 others over the years.

Everything worked except: the engine wouldn't run with the spout jumper removed. Changed back to the distributor mount & removed the extension harness & the engine runs with the spout removed.

This should tell you how important grounding & shielding is.

nothwoods · May 22, 2014

I like your car blown88, it's looks like mine except for the Cobra bumper... or least like what it looked liked a couple weeks ago before I disassembled it down to the bare shell. So far this week I have around 50 hours into modifying the electrical harnesses and metal fabrication under the hood-sorry I haven't kept up with this thread very well!

Blown88GT · May 23, 2014

nothwoods said:
I like your car blown88, it's looks like mine except for the Cobra bumper... or least like what it looked liked a couple weeks ago before I disassembled it down to the bare shell. So far this week I have around 50 hours into modifying the electrical harnesses and metal fabrication under the hood-sorry I haven't kept up with this thread very well!

It's not a Cobra bumper. I designed the pattern & cut it out with a hole saw & a jig saw. Under the hood, not even close. Color is probably the same, mine is original paint.

nothwoods · May 23, 2014

Nice job!

jrichker · May 25, 2014

Blown88GT said:
I made a shielded & grounded cable from a junkyard Ford one. Did it exactly like I designed 100 others over the years.

Everything worked except: the engine wouldn't run with the spout jumper removed. Changed back to the distributor mount & removed the extension harness & the engine runs with the spout removed.

This should tell you how important grounding & shielding is.

@Blown88GT
Only 1 end of the shield gets grounded. Which end did you ground?

nothwoods · May 25, 2014

Why couldn't you ground both ends? Is the shielding made of aluminium?

jrichker · May 27, 2014

Only one end gets grounded. This eliminates the shield ground from carrying any current between ground points. The current creates ground loops due to the difference in voltage between the 2 ground points.

The best shielding is aluminum foil wrapped around the wiring, and covered with a copper braid and insulation.

nothwoods · May 27, 2014

I'm splicing in where the existing TFI harness comes off at the firewall, could I just wrap my new sections in foil and copper braiding and overlap a few inches of the part that leads back to the PCM? The ground for the sheilding is near the PCM.

jrichker · May 27, 2014

That should work. Check the end to end resistance of the shield/braid. It should be less than 1.5 Ohms

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