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Old 10-20-2019, 12:11 PM   #1
GrannySShifting
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Default 0-5v sensor noise

Logging on OEM pcm some of the pressure sensors dont have clean readings. Is there some way to clean these up so they log a little more stably? The factory pressure sensors on these inputs are pretty stable
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Old 10-22-2019, 07:05 PM   #2
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Default Re: 0-5v sensor noise

How are the sensors powered and grounded ?

From clean 5v and 0v lines ? And are they good quality sensors ?
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Old 10-22-2019, 09:40 PM   #3
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Default Re: 0-5v sensor noise

Shielded cable used for harness?
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Old 10-22-2019, 10:26 PM   #4
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Default Re: 0-5v sensor noise

Not shielded but never really had issue before on other cars.

Using factory 5v feeds, these were originally 0-5v sensors used for pressure (fuel tank pressure sensor for example had a 1bar MAP sensor on tank top)

Is there soure to get "shield" to wrap around whats already wired up, does that work?
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Old 10-23-2019, 12:06 AM   #5
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Default Re: 0-5v sensor noise

What you want is shielded and or twisted and shield grounded at only one end. This is known as a "Faraday shield." If you don't have / can't get shielded you can "scrape by" with something like CAT5. Use one or two pair for your sensors, and ground the other pairs at one end. They will act as a shield/ ground plane. Twisted cable IE phone/ CAT5 is done for a reason. If you can find some old exposed overhead phone/ telegraph wires, typically along RR, you will find a "twist" periodically at the pole insulators. There will be a group "box" of 4 insulators, where the wires cross over to form the twist. Like so:


The 4 insulators grouped at right about the 5th crossarm down



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Old 10-23-2019, 12:11 AM   #6
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Default Re: 0-5v sensor noise

............Or click the link cannot get this photo to display





https://www.reddit.com/r/Damnthatsin...r_a_wild_fire/


There are all sorts of shielded wire. I bought some short cut color coded lengths off egag when I started the Megasquirt project, and still have not finished
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Last edited by 440roadrunner; 10-23-2019 at 12:14 AM.
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Old 10-23-2019, 02:06 AM   #7
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Default Re: 0-5v sensor noise

capacitor across the input. Big cap will slow response time. try .1 UF .
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Old 10-23-2019, 11:07 AM   #8
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Default Re: 0-5v sensor noise

Had this issue once before. I would be focusing on the source of the noise.

Did this just start? Was anything changed around the same time this started? Non-resistor plugs? "Performance" wires or coils? Bad coil? Alternator? Any other electrical components recently added? In my case, it was the addition of IGN-1A coils and Firecore wires. The problem wasn't so much the coils and wires but the ECU not having sufficient protection. Drove me nuts and tried everything being suggested. Went back to OEM coils and a different wire and haven't looked back since.
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Old 10-23-2019, 04:59 PM   #9
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Default Re: 0-5v sensor noise

Shielding may help...but it really should not be necessary, especially if other senors are not having the same problems.

Can you re-purpose and swap a noisy input, with a clean one, to see if the problem follows ?
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Old 10-24-2019, 12:44 AM   #10
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Default Re: 0-5v sensor noise

If you have a scope, make sure supply and gnd signals are clean. If gnd noise, check for loose gnd or gnd loops (multiple gnd points vs common gnd pole). Best practice - make sure to not route sensor wires by coils or other higher speed switching signals. As mentioned above, twisted pair or better yet shielded sense signal is best.
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Old 10-24-2019, 01:45 PM   #11
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Default Re: 0-5v sensor noise

There can never be multiple ground points as such for sensor wiring. They MUST all reference only to sensor grounds on the ecu which are dedicated for that purpose alone. If someone has connected to vehicle/engine/chassis ground that could result in noise or skewed readings.
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