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Old 07-05-2018, 04:43 PM   #1
durk80
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Default Shielded vs. Non-shielded wire question

I would like to run new wire from the crank position sensor to the ECU. My 91 240 3.1 has been giving me some problems, and would like to know if I could run regular automotive wire for the three connections vs. the shielded wire that is on there now. I'm not sure what problems it would cause, such as significant EMF noise from the engine causing it to run poorly- which maybe could be eliminated by braiding it in a ponytail.

I suspect the wiring because The CPS was bought about a year ago. I put some wire wrap around the cable to keep it from getting chewed up.


If this is a terrible idea, does anyone know of a store that sells this kind of wire?

Thanks as always!
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Old 07-05-2018, 04:55 PM   #2
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That isn't the way to do it because braiding doesn't stop other signals from being induced into the wiring. The foil shielding is there so other signals, for example the high voltage ignition noise won't be induced into the wires.
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Old 07-05-2018, 07:47 PM   #3
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Here's a link for shielded 2-wire cable: https://www.diyautotune.com/product/...2-gauge-10-39/

Or, you could try using a piece of USB 2.0 cable - the inner wires are pretty small (maybe 28 AWG?). Electrically, they'll be fine but mechanically they may be too fragile for an engine compartment.

edit: you might get lucky and find a USB cable with bigger power/ground wires:
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Old 07-05-2018, 09:58 PM   #4
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Thank you dl242gt!
Quote:
That isn't the way to do it because braiding doesn't stop other signals from being induced into the wiring. The foil shielding is there so other signals, for example the high voltage ignition noise won't be induced into the wires.
Would this do the trick if I can fit the insulated wires inside 18 or 16 gauge? https://www.ebay.com/itm/Tubular-Bra...-/291978557481

bobxyz thank you as well!!
Quote:
Here's a link for shielded 2-wire cable: https://www.diyautotune.com/product/...2-gauge-10-39/
I have seen other wire for sale like this with the same gauge, but for some reason, I feel that 22 gauge is too small for what is on there now, yet I would buy it if it would be reliable for my application. I am actually considering going the micro or mega squirt kit route, since it is probably close to the cost of a new MAF sensor.

Thank you guys for some sound advice and ideas!
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Old 07-06-2018, 03:07 PM   #5
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https://www.mouser.com/Tools-Supplie...yzv2xqZ1yz7zln

Wrap the wires in that, then add heatshrink.
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Old 07-06-2018, 04:20 PM   #6
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Originally Posted by woodenpudden View Post
https://www.mouser.com/Tools-Supplie...yzv2xqZ1yz7zln

Wrap the wires in that, then add heatshrink.
Excellent! I can't wait to try it out after I get done moving.
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Old 07-07-2018, 01:16 PM   #7
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FYI it is important for the wire to be the correct gauge size. Using a small size wire for that signal provides the signal to the ecu in the amplitude that works.
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Old 07-08-2018, 11:05 AM   #8
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I'm going to test Tasker 0,5 mm shielded microphone cable for next ECU project.
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Old 07-08-2018, 11:06 PM   #9
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I cut into the cable today with utility shears after it didn't make a mark in the insulation using the 18 or 20 gauge location on my wire strippers. Maybe it is 22 gauge like the 2 core shielded offered by megasquirt. https://www.diyautotune.com/product/...#tab-questions

The copper strands had definitely suffered some oxidation.

I considered the microphone wire as well, but was worried that it wouldn't last from the engine heat, so I decided I will try some 18 gauge copper 150 strand with a silicone jacket. This will then get wrapped with a bare wire, overlaid with conductive copper foil tape, and stuffed into heat shrink. I will post the results when it's finished!
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Old 07-09-2018, 09:34 AM   #10
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When you create your shielding cover, it needs to be only grounded on one end, and make the ground attachment as close to the ECM ground to rid as much noise as possible.
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Old 07-09-2018, 07:27 PM   #11
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If you're wiring all the way from the EZK to within an inch of the CPS sensor body, then yes, you want to connect all 3 wires at the EZK but leave the shield/drain wire disconnected at the sensor end. If you retain the stock CPS sensor with connector and cable stub (roughly 12" of cable), you want to connect both ends of all 3 wires. The shield/drain will be unconnected right at the CPS sensor.

If it were me, I'd get the DIYauto cable and just do a good job of adding strain relief / heat shrink at the connector.
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Old 07-29-2018, 11:06 AM   #12
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Quote:
Originally Posted by bobxyz View Post
If you're wiring all the way from the EZK to within an inch of the CPS sensor body, then yes, you want to connect all 3 wires at the EZK but leave the shield/drain wire disconnected at the sensor end. If you retain the stock CPS sensor with connector and cable stub (roughly 12" of cable), you want to connect both ends of all 3 wires. The shield/drain will be unconnected right at the CPS sensor.

If it were me, I'd get the DIYauto cable and just do a good job of adding strain relief / heat shrink at the connector.
I rewired the female three wire connector at the firewall for the Crank sensor to EZK. I did connect the shielding to both ends (ezk and cps sockets) because that was what it was like when I removed the pins. I then plugged in the new crank position sensor to the female socket.

Did I do this correctly, or do I need to omit the middle shield wire at the female connector for the CPS?

The reason why I am asking is because there was absolutely no change in the performance, as well as the check engine light went on and gave me the 131 code "engine rpm signal missing"--no other codes were present.

It says in my Haynes manual that the check engine light shouldn't illuminate for the 131 code, yet it surely did. This same code happened again after running the new wiring and installing a new bougicord crank sensor with the same bad idle.
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Old 07-29-2018, 12:48 PM   #13
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The ecu may have set more than one code. You have to let it roll through three times when checking. Up to three differents can be stored. Plus the ezk and the fuel computer can both set the light.
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Old 07-29-2018, 12:58 PM   #14
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Try another ECU.
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Old 07-29-2018, 08:26 PM   #15
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Quote:
Originally Posted by dl242gt View Post
The ecu may have set more than one code. You have to let it roll through three times when checking. Up to three differents can be stored. Plus the ezk and the fuel computer can both set the light.
Thanks for the help dl242gt, I did cycle through until I got the same code again. It was the only one stored. I didn't go through it three times though. I'll have to wait for it to come on again to try out that trick.

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Try another ECU.
After swapping in a different EZK unit, there wasn't a change either.
This is leading me to suspect that it is the computer since everything else checked out for the most part (except for the AMM heated film check which was off by an ohm 107 instead of 108. Not sure if this 1 ohm difference would make a drastic change in drive-ability/ idle.

The ECT sensor appears to be in range too. I measured 1,100 ohms from pin 13 to ground at the ECU harness unattached. It was with a cold engine at 93 degrees F today.

Before I drop more money on this problem I've been having since I bought this car, can I take the ECU apart to see if there are any cold solder joints?
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Old 07-30-2018, 08:50 AM   #16
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I think the 131 code due to the RPM wire that runs from the EZK to the ECU box. The wire is all within the cabin, so it's unlikely to have been damaged. I'd inspect the EZK and ECU connectors carefully, and maybe get a can of spray electronic contact cleaner at home depot.

The RPM wire is pin 17 on the EZK - with cable on left, pin 14 is the leftmost start of the bottom row.
On the ECU, RPM is pin 1 - with cable on left, pin 1 is the leftmost pin on the top row.
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Old 07-30-2018, 07:26 PM   #17
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1 ohm of difference doesn't mean anything. Especially on anything but a high end meter.
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Old 08-01-2018, 11:32 PM   #18
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Thanks for the responses. I have inspected the wires and connectors, cleaned the terminals, and the check engine light came on again. Drove the car to work, didn't let it warm up fully, and I went to pull out on to the main road, I pressed down on the throttle, and it sounded like I hit a rev limiter at approximately 1000 rpms. If you are familiar when you back up on a 4 wheeler and don't press the button on the handle to allow it to go faster. I pressed the gas further to the floor and eventually 'caught' and was fine.

Anyone ever had this problem?
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