Spark advance help
#1
03-06-2019
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Location: Los alamos
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Spark advance help
Here are some picture of live stream data on my 1996 2.3, I’m wondering if this is a regular pattern for the spark advance? There are three pictures; one at idle(warm), one at ~2100rpm and one more after letting off the gas and letting it decelerate. Any comments would be greatly appreciated! (Sorry it’s all out of order)
#2
03-06-2019
Welcome to the forium
A quick guide to spark timing
You/we want each cylinder to get FULL explosive power at about 8-10degrees AFTER Top Dead Center(ATDC), the space above the piston is still small and the Piston and Connecting Rod will have the best LEVERAGE to push down on the crank journal to add power to the cranks rotation.
So every thing works backwards from there as far as calculating the best time to spark BEFORE TDC(BTDC)
The biggest issue is the air fuel mix because it varies
Say a regular 14.7:1 mix takes 100milliseconds from spark to FULL explosion, it takes time for the flame front to fully ignite all the fuel, its not instant
But a Richer mix, say 13.5:1 only takes 50ms from spark to FULL explosion, rich mix ignites much faster
(100ms and 50ms are made up numbers for this example, you can find out real numbers and do the math for this, its all available online)
And then there is the time it takes for crank to travel from 20deg BTDC to 10deg ATDC, obviously crank speed at 2,000 RPM is rotating twice as fast as crank at 1,000 RPM, so it takes half the time, at 4,000 RPM 4 times as fast so takes quarter of the time
So RPM is a BIG BIG deal, but way more predictable than air:fuel mix
With a distributor there were springs and weights inside, as RPMs increased the weights move out away from center advancing the spark because regular mix still takes the 100ms to exploded but crank is moving faster so spark has to happen earlier so it still explodes at 10deg ATDC
And there was Vacuum advance, this was there for the fuel mix spark timing, as you step on the gas fuel mix gets Richer so you need the spark to retard a bit, because it burns faster
Well, Vacuum in the intake drops as you step on the gas, so vacuum advance retards spark timing when you step on the gas and then when you reach cruising speed vacuum in intake is back to normal as is air:fuel mix, so RPM advance is all you need, the weights and springs
With full computer controlled spark it gets much easier, because you have RPM and air:fuel all done by the same device and it also fires the Coils, the computer does all the math
So yes 20-25degBTDC is not unusual, neither would 9degBTDC
Probably get past 30-35 at 5,000RPM
And outside of having the computer tuned you can't change it
If you are having a spark issue unplug the 3 wire connector on one of the coil packs and start the engine, it should run smooth, if its missing then one of its spark plugs or wires is bad
Then do same test on other coil pack
This makes sure all spark plugs are working
There are some misconception about the dual coil/dual spark plug setup
All 8 spark plugs work all the time
Both spark plugs in each cylinder fire at BOTH TDCs, compression stroke and exhaust stroke, this is not for better emissions, lol, its just simpler to do this "Waste Spark" timing
Dual spark plugs give better performance always have, just hard to get that 2nd spark plug in a head, especially on a V6 or V8, lol
When engine makers when to 4 valves it was better than 2 spark plugs so dual plugs were not used on Ford 4cyl engines anymore
A quick guide to spark timing
You/we want each cylinder to get FULL explosive power at about 8-10degrees AFTER Top Dead Center(ATDC), the space above the piston is still small and the Piston and Connecting Rod will have the best LEVERAGE to push down on the crank journal to add power to the cranks rotation.
So every thing works backwards from there as far as calculating the best time to spark BEFORE TDC(BTDC)
The biggest issue is the air fuel mix because it varies
Say a regular 14.7:1 mix takes 100milliseconds from spark to FULL explosion, it takes time for the flame front to fully ignite all the fuel, its not instant
But a Richer mix, say 13.5:1 only takes 50ms from spark to FULL explosion, rich mix ignites much faster
(100ms and 50ms are made up numbers for this example, you can find out real numbers and do the math for this, its all available online)
And then there is the time it takes for crank to travel from 20deg BTDC to 10deg ATDC, obviously crank speed at 2,000 RPM is rotating twice as fast as crank at 1,000 RPM, so it takes half the time, at 4,000 RPM 4 times as fast so takes quarter of the time
So RPM is a BIG BIG deal, but way more predictable than air:fuel mix
With a distributor there were springs and weights inside, as RPMs increased the weights move out away from center advancing the spark because regular mix still takes the 100ms to exploded but crank is moving faster so spark has to happen earlier so it still explodes at 10deg ATDC
And there was Vacuum advance, this was there for the fuel mix spark timing, as you step on the gas fuel mix gets Richer so you need the spark to retard a bit, because it burns faster
Well, Vacuum in the intake drops as you step on the gas, so vacuum advance retards spark timing when you step on the gas and then when you reach cruising speed vacuum in intake is back to normal as is air:fuel mix, so RPM advance is all you need, the weights and springs
With full computer controlled spark it gets much easier, because you have RPM and air:fuel all done by the same device and it also fires the Coils, the computer does all the math
So yes 20-25degBTDC is not unusual, neither would 9degBTDC
Probably get past 30-35 at 5,000RPM
And outside of having the computer tuned you can't change it
If you are having a spark issue unplug the 3 wire connector on one of the coil packs and start the engine, it should run smooth, if its missing then one of its spark plugs or wires is bad
Then do same test on other coil pack
This makes sure all spark plugs are working
There are some misconception about the dual coil/dual spark plug setup
All 8 spark plugs work all the time
Both spark plugs in each cylinder fire at BOTH TDCs, compression stroke and exhaust stroke, this is not for better emissions, lol, its just simpler to do this "Waste Spark" timing
Dual spark plugs give better performance always have, just hard to get that 2nd spark plug in a head, especially on a V6 or V8, lol
When engine makers when to 4 valves it was better than 2 spark plugs so dual plugs were not used on Ford 4cyl engines anymore
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