Hydra w/Saturn Knock Sensor Wiring? - Miata Turbo Forum - Boost cars, acquire cats.

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Old 04-16-2013, 03:57 AM   #1
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Default Hydra w/Saturn Knock Sensor Wiring?

Hey all. I finally took the plunge and swapped from my AEM to the Nemesis from FM. I'm already so much happier with the unit and I only have a few hours of work into it. I have just about everything hooked up at this point, and the car starts, runs, drives, throttle pumps, and even almost idles well.

One of the last things to hook up (possibly THE last thing, actually...) is the Knock sensor. On the AEM, I had it hooked into the one wire knock input, and grounded the shield wire into a shared sensor ground somewhere in the harness in the engine bay. However, the Nemesis comes with the shield wire directly connected to the EMS.

Is it bad mojo to wire my existing knock sensor wire (which is nicely embedded into my front harness) up to the hydra as is, and then run its knock ground to the sheath of the existing wire, or does having a big loop like that create lots of RF interference? Digging the existing wire out of the harness would be quite a pain, but not undoable if it's the right thing to do. If it actually just creates more common shared grounds, then so much the better, I'll just do that.

Thanks!
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Old 04-16-2013, 10:26 AM   #2
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Just run the coax along the MAP sensor path. The knock sensor detects noise, the shielded coax cable shields noise interference. You've spent this much time/effort on an ECU, why cheap out on the 30 minutes of work for the primary sensor designed to keep your engine de-ventilated?
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Old 04-16-2013, 02:07 PM   #3
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Sorry, it was midnight and I didn't phrase it well.

The question is more about what is a better option:
1. Just run the new wire, don't ground it anywhere along the way, all the way from the Nemesis to the sensor.
2. Run the new wire into the existing wire, and connect both the signal wire and the shield, so it's grounded both at the nemesis and near the sensor into a different ground.

1 and 2 are probably similar amounts of time to do, so it's more a question of which one is actually superior -- i.e. is there any advantage to having the shield grounded near the sensor already, or is that either not helpful or detrimental?
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Old 04-16-2013, 02:45 PM   #4
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I'm guessing you have a hydra 2.7. After the dealings I've had with hydra 2.6 and the ems4 they have come out in about a wash imo. Maybe once I attach the ems4 with renewed vigor next weekend after actually reading the manual it might pull ahead of the hydra 2.6.

On the wiring, I'd just completely re-do the wiring like hydra wants it.
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Old 04-16-2013, 05:30 PM   #5
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Run the coax cable - one end connected to the hydra, one end connected to the sensor, no connections anywhere else.
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Old 04-16-2013, 07:07 PM   #6
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Okay, will do. Thanks!
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