Tom M'Guinn

Can anyone point me to a good source for 2-connector shielded wire for the speed and reference sensors? Mouser only seems to sell it by the mile...

Bri Bro

This is auto temp rated wire but you also get connectors you may not need. Any electronic supply house has it by the foot, just be careful of the operation temps of the insulation. These cars get hot under the hood.

http://www.jegs.com/i/MSD+Ignition/121/8862/10002/-1

Tom M'Guinn

Thanks Brian -- looks good!

Tom M'Guinn

Got that wire from Summit and it looks good (foil shielding with an uninsulated wire running the length of it). My ref sensor wires were nearly severed entirely at the connector, so I opted to re-use the factory wire and just put new pins and connectors on the end (courtesy of Johnkoawood's group buy). It a tight squeeze working on the wires with the motor still assembled, but was able to replace the connector without disassembing anything. Starts like a champ now. Of course, it was intermittent, so will have to wait to make sure all is well.

BTW, there seems to be a typo in clark's-garage ref sensor page, or I am confused by his reference to pin 78 in his connector chart...?

JohnKoaWood

WOOT!

And I just confirmed today, I do have 50 feet of 2 conductor shielded wire on hand..

Glad it all got worked out for you!

Tom M'Guinn

Thanks for your PM John. I was sure happy to have your connectors handy when I saw those wires. Everything worked like a charm. Thanks!

951Doc

Aircraft Spruce is also a good source for shielded multi-wire cable. The stuff they sell is Mil-Spec'd Tefzel, pretty good stuff which holds up well under stress.

http://www.aircraftspruce.com

Ronin-951

Remember to only ground one end of the shield for EM protection.

Tom M'Guinn

Please school me on shielded wire. The MSD wire is shielded with a thin foil, whereas the stock wire is shielded with a thick covering of braided wire. The great unwashed internet says foil is better for RF interference, while braided while is better for EMI. Any insights on that? What are we shielding against under the hood -- EMI? I ask because I used a short chunk of that foil shielded wire and the car seemed to loose ignition at one point under WOT. I'm planning to replace the wires all the way to the DME but thought I'd throw this out there for any insights. Thanks all....

Ronin -- why only ground one end?

Bri Bro

EMI is the same as RFI. The braid shield and foil should work equally well for EMI generated by cars. The shielding is to prevent starter noise (brushes arcing cause RF) and ignition noise (sparks cause RF) from getting into the low level sensor leads. The sensor will create more voltage as RPM go up so they are at the lowest voltage while starting.

Grounding at one end is a common practice to avoid making a ground loop since the engine "ground" voltage will be a little different the the DME "ground" voltage which will cause a current to flow in the shield wire.. And yes, there are cases were you ground both side but that is normally not done in car wiring. Proper grounding of High power RF can be more of an art then a science.

You said the inner conductor didn't have insulation. I am guessing it was enameled insulation on the wire which is becoming very common in thin wire cables like earphone etc. The enamel is a very good insulator and that wire is what is used inside the sensors. Getting the enamel off of the wire can be a pain. I use a soldering iron to burn off the enamel and then tin the wire.

Tom M'Guinn

Thanks Brian. So if I had an ignition hiccup at WOT after grafting a foil shielded wire to a braided shielded wire, admittedly with some gaps near the connector, is there any real chance it was an interference issue -- or more likely an intermittent break somewhere further up the line?

Bri Bro

I would go back and look at the electrical connections to the wires and the pins and make sure the connections have good solder joints. WOT is also the largest vibration to the connections. You could also wrap the area of the connections of the shields in copper tape (attached to ground) to see if that helps. Intermittent problems are always the hardest to solve.
http://www.stewmac.com/shop/Electron...pper_Tape.html

JohnKoaWood

Brian in on the mark... Tom make sure to report back on your results!

EMI / RFI interference is problematic in cars, but deadly in aircraft.

Many of the early adaptations to address this on aircraft were done with less expensive foil wrapped multi conductor wire... with less than stellar results. Much of the foil wrapped cables have since been swapped out for braided wrap wiring, with much better results.

FWIW, I much prefer the braided shielding for wiring, it is more expensive in most cases, but also more effective at shilding for a wider range of interference frequencies.. in most cases!

Foil wrap is decent for static installs, where the interference is not a moving taget, the braided shilding is MUCH better at dynamic environments.. as it can handle a much broader frequency range without missing a beat!

YMMV

theedge

Ground loops and voltage differences. And to be clear, youd connect the shield of the speed and reference sensors to the shield of the wire, using all three pins on the connect.

Tom M'Guinn

Wow, thanks guys. Who knew there was so much shielding info out there. I found a few wire mfg presentations online and they all seem to say about the same. In the meantime, I opened up the DME connector so see what the other end of the wires looked like. The ref sensor wires were a bit croupled up in there, and the brown wire had a tiny little wrap of electrical tape around it. Under the electrical tape was a small tear/hole in the insulation for the brown wire. It looked well sealed, but suggests "somebody" was in there before. Also the twisted pair inside the shielding seemed molded together like speaker wire -- and I can't tell if that was by design, or if they had just started melding together from pressure and heat over the years. Anyone know? If the latter, then I wonder if it's shorting someone along the length? Either way, I threw pride aside and ordered a replacement from Lindsey. Will try it this weekend and report back. Thanks very much for all the info in the meantime!