how does the ecu determine the load on the engine?

[oab_au]

Originally Posted by THE NEW GUY

in the old times, the carburetor had a barb connector for a hose thar lead the the distributor to act on a diafragm to increase the ignition timing advance. This was the "LOAD" factor on the advance. The RPM factor was done with counterweights on the rotor.
We do not have distributors now. It's all on the chip. but I do not feel any increase of the ignition advance due to "load" on my SVX. May be the only way to confirm it, is with a camera and a timing gun, some tape and run the car....

To see why the ignition timing is advanced over the engines running conditions, you have to look at why we time it, in the first place.
The whole objective is to develop the pressure on the piston at about 15/18* after top dead center, when the con rod is at an angle, that can exert the force on the crank.
Now while the rate that the combustion chamber full of air/fuel burns, is basically constant, the speed of the engine is not. When the engine is idling the spark starts the burn at 10*BTDC this takes 25* at this speed to build up max pressure by 15* ATDC. As the engine increases speed, we have to light the fuel earlier to allow for the pressure to build up. So as the engine increases speed, we increase the spark advance to allow for the time that it takes for the fuel burn, to develop maximum pressure.

At about 2200/3000 rpm another factor starts to speeds up the burn rate.
This is the turbulence created by the squish of gas squeezed out of the space between the edge of the piston and the cylinder head squish area. This turbulence has been increasing over the last 1500/2000 rpm or so, but now it has got to the point that the increase in the burn rate due to the increasing turbulence keeps pace with the increasing engine speed. The Ignition Advance then remains constant at about 36* BTDC, from about 3000 up. This means it takes 51* to get maximum pressure on the piston at 15* ATDC.

The fuel mixture, turbulence, temperature and pressure, all affect the rate of the burn. Any change in the rate of the burn requires a change in the Ignition advance to bring the maximum pressure back to 15*ATDC. So when we lift the foot, the cylinder pressure reduces, and the fuel mixture is leaned off. Both of these factors result in the burn taking longer, so the ignition timing is advanced, around 20* is added to the 36* to get the max pressure back to the 15/18* spot.

In the old distributor, the centrifugal weights advanced the timing with the rpm rise. The Vacuum advance worked to advance the timing, when the vacuum is high, that is when the cylinder pressure is low, and the mixture is lean, and the burn rate is slow.

Harvey.

[kwren]

Originally Posted by THE NEW GUY

I do not feel any increase of the ignition advance due to "load" on my SVX.

I'll be that you would sure feel the difference if the ignition failed to advance due to "load".

The result of ignition advance is actually easy for me to feel when I need an increase in power.

Without the ignition advance there would be no increase in power. Probably just a bunch of sputtering.

Keith

[oab_au]

Originally Posted by kwren

I'll be that you would sure feel the difference if the ignition failed to advance due to "load".

The result of ignition advance is actually easy for me to feel when I need an increase in power.

Without the ignition advance there would be no increase in power. Probably just a bunch of sputtering.

Keith

Keith, no it is the other way around. When you are cruising along on a steady throttle, the ignition advance is the 56* maximum.
When you floor the throttle, the ignition timing retards this 56*, back to the full load 36* BTDC.
Once the engine is under full load, the advance stays the same 36* at all rpms above 2500, doesn't change.

Harvey.

[THE NEW GUY]

Originally Posted by oab_au

The Vacuum advance worked to advance the timing, when the vacuum is high, that is when the cylinder pressure is low, and the mixture is lean, and the burn rate is slow.

Harvey.

Hi Harvey. Its nice to hear from you.
But this is not accurate. the vaccum hose that connect to the distributor is conected so the vaccum is aplied on the distributor's diafragm only if you press the gas pedal a few, and it's proportionally to the throttle position. there's a poit where no more vaccum is aplied to the diafragm because there's no more vaccum on the intake manifold. this hose comes from the throtte body, not from the intake manifold.
Anyways, your explanation is so clear. Do you think a vaccum sensor would help our subarus SVX to perform better? (with a new chip of course)
do you have the 1av1 chip? (stage 1 intalled in your car)
Thanks

[b3lha]

Originally Posted by oab_au

I think you have their actions, in reverse.

Thanks Harvey.

In order to redeem myself let me post some pictures of the actual SVX ignition timing maps extracted from various ECUs in my collection.



On the left is the base (minimum) timing map, for low octane fuel. On the right is the advance map. A percentage of the advance map gets added onto the base map depending on the amount of knock detected. If you have good fuel and never get any knock, then your timing will be base + 100% of the advance.

It's interesting to note that the Euro and US base maps are very similar, but the Euro car is allowed to add more timing at high rpm and load. But the JDM one is way ahead. At 4400 rpm and 64 load JDM timing is (17 + 11)=38 degrees whereas the USDM is (10+10)=20 degrees. Eighteen degrees difference!

That's why my JDM runs so much better on 98 octane than 95. I am sure that a local garage ripped me off recently by putting 95 in their 98 pump. As soon as I drove away I felt the drop in power as the ECU pulled the timing right back.

But anyway, I digress. As you can see, timing does indeed increase with engine load. But I don't really understand what you intend to do with a MAP sensor, unless you have a standalone ECU. I think modifying the stock ECU to take input from a MAP sensor and incorporate it into the load calculation would require a significant amount of expertise.

[icingdeath88]

Originally Posted by b3lha

I think modifying the stock ECU to take input from a MAP sensor and incorporate it into the load calculation would require a significant amount of expertise.

This. Actually, this seems like an understatement.

[bazza]

Interesting how much timing they can run in NA mode. Here's a conservative timing map for a stock EG33 with a turbo (E85):

[icingdeath88]

Originally Posted by bazza

Interesting how much timing they can run in NA mode. Here's a conservative timing map for a stock EG33 with a turbo (E85):

Remind me, what kind of ECU are you running again?

[bazza]

Originally Posted by icingdeath88

Remind me, what kind of ECU are you running again?

It's a LinkPlus G3 full wire in unit.

[THE NEW GUY]

impresive, all your answers. thanks guys.
now, I have read somewhere, that stock ecu can adjust injection only 4% up and 4% down due to O2 sensors. Is it correct?
If so, that give me only 4% reduction in gasoline consuption if I inject HHO as an alternative fuel combined with gasoline. It doesn't worth the effort...