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Flex Fuel Sensor Wiring With Holley

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Old Aug 7, 2022 | 10:05 AM
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Default Flex Fuel Sensor Wiring With Holley

Folks, I know this is probably not the correct forum for this question, but I wanted to get as much feedback as possible and this forum will most likely have more folks who use a flex sensor and Holley ECU.

I mentioned Holley (HP) ECU but not sure if makes a difference how it's wired with any other ECU. I've read 5V, sensor ground and signal and 12V, ground and signal. On the Holley forum they say 12V, ground, signal and 5V with a 10K resistor on the 5V tied into the signal for amplification. I have a buddy with a Continental/GM sensor wired on a MS3 with 5V and sensor ground and It's off by a couple of % but consistent. Using 5V and sensor ground makes sense to me as, unlike 12V and chassis ground, there would be no variance in voltage.

So, how have you folks wired it up and is it fairly accurate and consistent?

TIA,
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Old Aug 7, 2022 | 11:42 AM
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Originally Posted by 2JZFC
Folks, I know this is probably not the correct forum for this question, but I wanted to get as much feedback as possible and this forum will most likely have more folks who use a flex sensor and Holley ECU.

I mentioned Holley (HP) ECU but not sure if makes a difference how it's wired with any other ECU. I've read 5V, sensor ground and signal and 12V, ground and signal. On the Holley forum they say 12V, ground, signal and 5V with a 10K resistor on the 5V tied into the signal for amplification. I have a buddy with a Continental/GM sensor wired on a MS3 with 5V and sensor ground and It's off by a couple of % but consistent. Using 5V and sensor ground makes sense to me as, unlike 12V and chassis ground, there would be no variance in voltage.

So, how have you folks wired it up and is it fairly accurate and consistent?

TIA,
Im wired as per the Holley instructions but WITHOUT the resistor. I haven’t tested fuel in a while, but the ethanol level changes accordingly.
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Old Aug 7, 2022 | 12:04 PM
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Thanks for the quick reply.

To make sure I am not misinterpreting your response, I assume you mean 12V and chassis ground. Also, when you say you haven't tested fuel in a while, do you mean it's working but you haven't done a comparitive test like against the Quick Fuel tester?
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Old Aug 7, 2022 | 12:17 PM
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I took the easy way out and my tests match the readings..
Cheap enough option. https://www.currentperformance.com/s...nator-harness/
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Old Aug 7, 2022 | 12:20 PM
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Mines wired per Holleys instructions and seems to work fine.
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Old Aug 8, 2022 | 06:51 AM
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Wired using chassis ground, 5v reference wire I needed the resistor. Tons of people including myself had issues with small flex sensor and I had to change to the larger sensor with the mounting tabs. Works flawless now!
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Old Aug 8, 2022 | 06:58 AM
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Thanks, Guys.
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Old Aug 9, 2022 | 05:21 AM
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I have wired them per Holley's instructions, but last one I used the wiring sold thru Sloppys, made it easy, plus it had the alt wiring, so I am using one again on the new build. I use the GM sensor, noticed each time they read 8% vs the 10% listed at the pump. Never tested the fuel, other than E85 from the pump.
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Old Aug 10, 2022 | 11:05 PM
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On my last car I wired it up with the resistor. This time around I bought the e85/alt harness from Current Performance.
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Old Aug 11, 2022 | 01:10 PM
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https://documents.holley.com/techlib...r10864rev1.pdf

page 13

Andrew
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Old Aug 15, 2022 | 10:15 AM
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I wired mine in with the resistor and it worked great.
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