Timing advance displays on OBDII apps
Thursday 4th May 2017
Cranking compression is around 190 psi. 15 degrees initial, 21 mechanical (all in by 3000 RPM), and the current vacuum can adds 20 degrees. That all adds up to 56 degrees when cruising in 4th. Running 91 octane I will hear a little rattling at cruise.
I have bought myself a cheap wireless ELM327 dongle for the car, and have been running the Four Stroke app on iOS to play about with the various readouts. I was interested in measuring ignition advance (for example between V-Power, Momentum 99 and 95 RON) but the display has me doubting myself. It is labelled 'Ignition timing advance on cylinder #1', and shows a display varying from (approx) -30 degrees to (+)50 degrees.
Since the display is labelled timing advance, I would expect the positive numbers to be actual advance, and (somewhat confusingly) the negative numbers to be 'not advance' (i.e. retardation). However that's obviously a double negative, and in a way it'd make more logical sense for the minus numbers to be advance and the positive numbers be retardation. The app could have been clearer, I know! I also tried OBD Fusion but that displays in exactly the same format.
Generally speaking, after a quick play, the numbers seem to be negative values at idle and to be highest into positive (advance?) when under light load. Under heavier acceleration the number falls closer to zero (eg +7 or +10, versus +25 or +30 under lighter throttle). That to me suggests I was right at first impression - normal positive numbers are indeed advance, and negative are actually retardation.
Wiki posts, Google searches and the documentation for the apps weren't helpful. So, can anyone here please give me the correct answer to save me waiting days for the developers to reply? Thanks in advance (ha!).
Since the display is labelled timing advance, I would expect the positive numbers to be actual advance, and (somewhat confusingly) the negative numbers to be 'not advance' (i.e. retardation). However that's obviously a double negative, and in a way it'd make more logical sense for the minus numbers to be advance and the positive numbers be retardation. The app could have been clearer, I know! I also tried OBD Fusion but that displays in exactly the same format.
Generally speaking, after a quick play, the numbers seem to be negative values at idle and to be highest into positive (advance?) when under light load. Under heavier acceleration the number falls closer to zero (eg +7 or +10, versus +25 or +30 under lighter throttle). That to me suggests I was right at first impression - normal positive numbers are indeed advance, and negative are actually retardation.
Wiki posts, Google searches and the documentation for the apps weren't helpful. So, can anyone here please give me the correct answer to save me waiting days for the developers to reply? Thanks in advance (ha!).
Thursday 4th May 2017
Normally minus is degrees before top dead centre i.e. advanced timing and plus is degrees after i.e. retarded
There's usually a base timing which might for example be -10 degrees and all timing values will be relative to this base timing, but whether the obd2 reports relative to base or relative to 0 degrees is going to be hard to figure out
at idle you'd expect to see some mildly advanced timing and light throttle at high speed should show very advanced timing, full throttle and low speed will show less advance. Though if it's showing + numbers it might be just that the number is realtive to base timing but still before top dead overall.
To check the effect of different fuels you'll be looking for the values at full throttle at low speed and at peak torque as this is where knock is most likely to occur. If it will take more advance then it's a better fuel. Though not all engines are limited by fuel, some will take as much advance as they need without running into knock, these won't respond much to better fuel, others will run into knock before getting to optimal timing and these will respond to better fuel.
There's usually a base timing which might for example be -10 degrees and all timing values will be relative to this base timing, but whether the obd2 reports relative to base or relative to 0 degrees is going to be hard to figure out
at idle you'd expect to see some mildly advanced timing and light throttle at high speed should show very advanced timing, full throttle and low speed will show less advance. Though if it's showing + numbers it might be just that the number is realtive to base timing but still before top dead overall.
To check the effect of different fuels you'll be looking for the values at full throttle at low speed and at peak torque as this is where knock is most likely to occur. If it will take more advance then it's a better fuel. Though not all engines are limited by fuel, some will take as much advance as they need without running into knock, these won't respond much to better fuel, others will run into knock before getting to optimal timing and these will respond to better fuel.
Thursday 4th May 2017
Though if it's showing + numbers it might be just that the number is realtive to base timing but still before top dead overall.
I'd be very surprised if it ever gets to ATDC for ignition...Thursday 4th May 2017
Though if it's showing + numbers it might be just that the number is realtive to base timing but still before top dead overall.
I'd be very surprised if it ever gets to ATDC for ignition...Yeah I was surprised OP reported seeing +50 degrees unless its something weird emissions related that modern engines do under some circumstancesThursday 4th May 2017
Yeah I was surprised OP reported seeing +50 degrees unless its something weird emissions related that modern engines do under some circumstances
I should note that the gauges are fully customisable, and are generically populated when first created/added to the display in order for you to customise as you see fit. I've not actually seen timing outputs of that magnitude! Around mid 20s, though, certainly. As I said it seems to settle into approx +7 to +10 under acceleration and tips closer to +mid 20s on a steady/cruising throttle setting. It occasionally dips into the negative numbers, mostly when idling. Hence why the layout has confused me so much lol. Advertisement
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