How does VG respond to knock sensor? - Maxima Forums



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How does VG respond to knock sensor?

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Old 10-20-2017, 08:21 AM   #1
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How does VG respond to knock sensor?

Just a general question about the VG engine. How does the engine respond to the knock sensor. To my understanding it doesn't have variable ignition or valve timing so the only thing that leaves is fuel enrichment to reduce knock. Is that the case? Thanks.
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Old 10-20-2017, 04:43 PM   #2
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Exactly. And if it's faulty, which it probably isn't, you can replace it without tearing apart the engine.
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Old 10-24-2017, 10:03 PM   #3
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Just a general question about the VG engine. How does the engine respond to the knock sensor. To my understanding it doesn't have variable ignition or valve timing so the only thing that leaves is fuel enrichment to reduce knock. Is that the case? Thanks.
The ignition timing is variable, if you look at it with a computer it is constantly being adjusted based on load, rpm, temp, etc. If the ECU “thinks” (and I put that in quotes because a bad sensor or wiring can cause a false reading) then the timing is retarded to prevent knock.
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Old 10-25-2017, 11:20 AM   #4
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depends on what VG, W blocks retard spark, A-B blocks don't have a knock sensor
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Old 10-27-2017, 08:05 PM   #5
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depends on what VG, W blocks retard spark, A-B blocks don't have a knock sensor
True, but the Maxima only came with W blocks and a knock sensor.
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Old 10-27-2017, 10:08 PM   #6
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So that means the ecu can change the position of the distributor rotor?
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Old 11-02-2017, 02:26 PM   #7
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This is kind of a sidetrack, but my 85 300ZX has the earlier VG without a knock sensor. They didn't include a knock sensor on the non-turbo motors (which includes mine), but they did include them on the turbo model.
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Old 11-03-2017, 11:37 AM   #8
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Distributor rotor position cannot change. I am guessing that the magnet on the rotor is being detected by the sensor early, and the ECU sends the pulse later depending on the RPMs and knock sensor reading. But don't hold me to it, as I sold my 3d gen VG back in 2006 and can't remember how it worked. Back then I tried running premium gas with 20 degree advancement and found absolutely no improvement in power, so returned to the factory 15 and never touched the thing.
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Old 11-07-2017, 12:56 PM   #9
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So that means the ecu can change the position of the distributor rotor?
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Distributor rotor position cannot change. I am guessing that the magnet on the rotor is being detected by the sensor early, and the ECU sends the pulse later depending on the RPMs and knock sensor reading. But don't hold me to it, as I sold my 3d gen VG back in 2006 and can't remember how it worked. Back then I tried running premium gas with 20 degree advancement and found absolutely no improvement in power, so returned to the factory 15 and never touched the thing.
the rotor has enough area that the spark can be adjusted with signal timing, the distributor is locked which also has the signal disk integrated into it. The contact on the rotor is wide enough to almost reach the whole way between the pick ups in the cap





The trigger disk which is under the rotor is the one on the top, it has 360 slots on the outer and the 5 small and one large on the inside so the ECU knows where the engine is. The disk on the bottom is the one used for Megasquirt for full sequential (they haven't done the decoder for the high rez wheel for the MS3 and the MS 1 and 2 don't have the power to deal with it), adjusting the distributor in a factory set up will also adjust where the ECU thinks the engine is so will also effect things like injector timing, which isn't a super big deal on most of them since they are batch fire.

To give you kind of a idea of the range of the rotor, with it set where I have it I run a base timing of around 27 deg BTC and ramp up to around 37 and still have rotor left, but I haven't pushed it or got it on a dyno to set timing for power yet, but have heard of some people running like 50 deg.

If you put a timing light on and rev the engine you will see the ECU adjust the timing though the rpms
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Old 11-09-2017, 12:14 PM   #10
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Just to be clear, the timing set by adjusting your rotor is the base timing. The ECU can (and does) advance and retard the timing without moving the distributor. It is done electronically, and is based on many factors like engine speed, load, etc. If you are able to look at the timing (via Nistune or other) you can see that it constantly changing. The knock sensor is only one factor, and if knock is dectected it limits the upper range of advancement to help avoid it.
I think many people are confusing the base timing that you can adjust by moving the distributor, with modern cam timing which does adjust the gears mechanically.
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Old 11-12-2017, 12:28 PM   #11
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Thanks for the responses, I understand this better now.
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