Engine RPM falls switching into neutral - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

shoottothrill · 03-02-2021, 09:57 PM

Hey guys, I've got a KA S14, stock ECU, stock engine, stock most things. It is a factory auto, manual swapped, still using the stock 3D auto ecu.

What I'm finding is that when I have the clutch in 1st gear, it'll idle where I would expect, 800-900 rpm. Without moving anything else (clutch still in), and switching into neutral, the idle will fall to 500-600 rpm.

If the idle fell the opposite way, neutral to 1st, that would make a fair bit more sense to me. Is this a byproduct of having the auto ecu still in? Would swapping in a 3c manual ecu fix the issue? Anybody ever run into this issue?

Thanks for the info!

Silv1401 · 03-04-2021, 08:44 PM

Does it cause drivability issues?

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shoottothrill · 03-04-2021, 08:46 PM

Quote:

Originally Posted by Silv1401

Does it cause drivability issues?

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No, it's just very annoying.

Silv1401 · 03-04-2021, 10:42 PM

Duh fuq you posting for then? It's a 240. If you don't have the wherwithal to figure out the bug, then just gonna have to live with it lol. Also, fwiw, I don't think I've ever seen an actual good piece of advice come from this forum for anyone running an automatic transmission, besides the proverbial "manual swap it"

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shoottothrill · 03-04-2021, 10:44 PM

...if you'd actually read far enough, it is manual swapped. I'm just looking if anyone else has run into it.

If you haven't, you can see yourself out my dude

Silv1401 · 03-05-2021, 01:58 AM

Pfft, my bad, re read it.

Weird issue, could be the cpu getting signal from the neutral position sensor (if you happened to wire that in for some reason,) and dropping revs to normal idle speed. Likewise if you wired the top position sensor in as well, then the CPU would be getting signal for being in gear, so it is raising the idle in anticipation of counteracting the engine load. Theoretically. You could get under there and just unplug everything but the reverse light and speed sensor, and see if it changes anything. Those are the only two you really need anyways.

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03-02-2021, 09:57 PM	#1
shoottothrill Leaky Injector Join Date: Jan 2020 Location: Arizona Age: 28 Posts: 86 Trader Rating: (1) Feedback Score: 1 reviews	Engine RPM falls switching into neutral Hey guys, I've got a KA S14, stock ECU, stock engine, stock most things. It is a factory auto, manual swapped, still using the stock 3D auto ecu. What I'm finding is that when I have the clutch in 1st gear, it'll idle where I would expect, 800-900 rpm. Without moving anything else (clutch still in), and switching into neutral, the idle will fall to 500-600 rpm. If the idle fell the opposite way, neutral to 1st, that would make a fair bit more sense to me. Is this a byproduct of having the auto ecu still in? Would swapping in a 3c manual ecu fix the issue? Anybody ever run into this issue? Thanks for the info!

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03-04-2021, 08:44 PM	#2
Silv1401 Zilvia Member Join Date: Jan 2019 Location: Vancouver, WA/Portland, OR, USA Posts: 166 Trader Rating: (1) Feedback Score: 1 reviews	Does it cause drivability issues? Sent from my SM-N986U1 using Tapatalk

03-04-2021, 10:42 PM	#4
Silv1401 Zilvia Member Join Date: Jan 2019 Location: Vancouver, WA/Portland, OR, USA Posts: 166 Trader Rating: (1) Feedback Score: 1 reviews	Duh fuq you posting for then? It's a 240. If you don't have the wherwithal to figure out the bug, then just gonna have to live with it lol. Also, fwiw, I don't think I've ever seen an actual good piece of advice come from this forum for anyone running an automatic transmission, besides the proverbial "manual swap it" Sent from my SM-N986U1 using Tapatalk

03-04-2021, 10:44 PM	#5
shoottothrill Leaky Injector Join Date: Jan 2020 Location: Arizona Age: 28 Posts: 86 Trader Rating: (1) Feedback Score: 1 reviews	...if you'd actually read far enough, it is manual swapped. I'm just looking if anyone else has run into it. If you haven't, you can see yourself out my dude

03-05-2021, 01:58 AM	#6
Silv1401 Zilvia Member Join Date: Jan 2019 Location: Vancouver, WA/Portland, OR, USA Posts: 166 Trader Rating: (1) Feedback Score: 1 reviews	Pfft, my bad, re read it. Weird issue, could be the cpu getting signal from the neutral position sensor (if you happened to wire that in for some reason,) and dropping revs to normal idle speed. Likewise if you wired the top position sensor in as well, then the CPU would be getting signal for being in gear, so it is raising the idle in anticipation of counteracting the engine load. Theoretically. You could get under there and just unplug everything but the reverse light and speed sensor, and see if it changes anything. Those are the only two you really need anyways. Sent from my SM-N986U1 using Tapatalk