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Old 10-05-2019, 01:22 PM   #1 (permalink)
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How is ignition timing controlled?

I am wondering how a car's ECU controls ignition timing, in a general sense. I am well aware of the fact that the ECU advances and retards timing based on load, RPM, speed, intake air temp, coolant temp, throttle position, etc. But what I am wondering is if the ECU tries to advance the ignition timing as much as possible without the knock sensor detecting knock, or if the ECU just sets the timing to what it is programmed to and retards timing if it detects knock.

For example, if the car is cruising under a steady load and all other conditions stable, will the ECU advance the timing until it detects knock and then retard it slightly so the timing advance is always as much is possible, or does it just set the timing to what it is programmed to run at for the given conditions and leave it alone unless it is detecting knock? Thanks in advance!

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Old 10-05-2019, 01:32 PM   #2 (permalink)
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It is more or less pre programmed.

Tuners can change it.
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Old 10-05-2019, 01:37 PM   #3 (permalink)
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It is more or less pre programmed.

Tuners can change it.
Thanks. So it normally just runs at what it is pre programmed to and only retards timing if the knock sensor detects knock for some reason? Also, presuming the recommended fuel octane is used and everything is working correctly, would the knock sensor ever detect knock under normal conditions?
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Old 10-05-2019, 02:05 PM   #4 (permalink)
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In older fuel injected vehicles the knock sensor was used as a kind of a fail safe to keep them running smooth, only triggered by abnormal operations causing knock.
In newer engines it seems that the knock sensor is used as a real time instrument to provide vital computer input. It allows engines to get the best fuel economy running near stochometric air fuel mix buy running up to 50 and even 60 degrees of advance.
Modern engine control systems will keep adding timing advance while cruising down the road until a little knock is detected then the computer pulls timing back.
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Old 10-05-2019, 03:33 PM   #5 (permalink)
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Also, some of the older electronic fuel injection cars, such as a Civic DX, CX, OR LX from the 1990s, did not even have knocks sensors. Timing on suchvehicles must be entirely by pre-programing, I would guess.
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Old 10-05-2019, 04:07 PM   #6 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
In older fuel injected vehicles the knock sensor was used as a kind of a fail safe to keep them running smooth, only triggered by abnormal operations causing knock.
In newer engines it seems that the knock sensor is used as a real time instrument to provide vital computer input. It allows engines to get the best fuel economy running near stochometric air fuel mix buy running up to 50 and even 60 degrees of advance.
Modern engine control systems will keep adding timing advance while cruising down the road until a little knock is detected then the computer pulls timing back.
Great information, thank you! What would the knock sensor be used for on an 05 Civic? Would that be considered "modern"? Is it just a failsafe in case for some reason it knocks, or would it actually be used for realtime data so the ECU can optimize the timing?

To ask this another way, could simply using a higher octane fuel than what is recommended result in more ignition timing advance, or would nothing really change since there wouldn't be knock under normal conditions anyways? Thanks in advance
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Old 10-05-2019, 04:28 PM   #7 (permalink)
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You have confirmed that your 05 Civic has a knock sensor? An 05 is the last year of the d-series engine. Not all d-series engines had knock sensors. You will want to check with a good source, or better find it on your block.
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Old 10-05-2019, 04:36 PM   #8 (permalink)
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You have confirmed that your 05 Civic has a knock sensor? An 05 is the last year of the d-series engine. Not all d-series engines had knock sensors. You will want to check with a good source, or better find it on your block.
Yes, I know for a fact that my 05 has a knock sensor. I have seen it on the back of the block when I had the engine out to rebuild. Good point though!
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Old 10-06-2019, 12:40 PM   #9 (permalink)
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If the engine uses mass air flow to regulate the air and fuel going into the engine it's more likely to actively use the knock sensor.
I think the easiest way to tell would be to use a live obd2 monitor rig get an idea of what the timing looks like. If it only ever goes to around 40 degrees or so it probably runs a fixed timing table. If it goes over 50 it's probably using the knock sensor.
Then to confirm put a few gallons of premium gas from empty in it and it should run even more advance.
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Old 10-06-2019, 03:50 PM   #10 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
If the engine uses mass air flow to regulate the air and fuel going into the engine it's more likely to actively use the knock sensor.
I think the easiest way to tell would be to use a live obd2 monitor rig get an idea of what the timing looks like. If it only ever goes to around 40 degrees or so it probably runs a fixed timing table. If it goes over 50 it's probably using the knock sensor.
Then to confirm put a few gallons of premium gas from empty in it and it should run even more advance.
Thanks. Mine doesn't have a MAF sensor, and the timing advance doesn't seem to go much past 30 degrees. Using premium fuel doesn't seem to change the timing advance significantly, but it moves around so much that it's hard to say for sure. For some weird reason the timing always runs at around -8 degrees at idle, not sure why. But it has always done that, both with the stock ECU and with the JDM Honda Stream ECU that I am using now, so I guess it's normal.

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