injection timing

 fuel injection timing calculation

This is Abdulfatah from how EFI works comm and today I want to explain injector timing basically when do you want to start injecting fuel we're going to start with the basic assumptions or goals we want to minimize the pulse width and make the best use of the fuel we're sending into the motor maximize rpm assuming that we're not changing anything else you would think if the motor is more efficient the RPM

Would come up minimize the map the more the manifold absolute pressure this is basically what mechanics have been using for years when adjusting mixtures on a motor in a stable idle or some combination of all these this is the motor that I will be doing the experiment with this happens to be a Honda b18c I'm going to be using it on the low horsepower mode are the small cams so to speak VTEC is turned off in this motor it is an ITB we are having

The injection comes down just under the throttle plates about eight inches from the edge of the motor we're about 12 inches from the bottom of the air filter down to the intake valve on this motor so the injection is coming in pretty far up from the intake valves where you would normally get to this is under fuel settings injector timing table and from there pops up the injector timing table what you get when you open this table is a table that runs from idle or even

Below idle up through 7,000 rpm and from a load of 20 up through 100 in my case I happen to be using an ITV load but this normally would be manifold air pressure on a speed density system so let's talk about what this 360 means out in the field this is the normal engine cycle which goes through four stages intake compression power and exhaust and then repeats back into intake on our definition the top dead centre between

The compression and power stroke or 720 degrees or zero degrees it's all the same thing that happens just as the piston comes to the top dead centre right here in this drawing I'm showing the crankshaft at about 40 degrees after the top dead centre on the intake stroke so the piston is coming down on the compression stroke or about 40 degrees before top dead centre the piston would be coming up in compression zero degrees or tap dead centre drawn here is 40 degrees in

The power stroke as the piston is coming down the exhaust would be 320 degrees in the table where the piston is coming up in this picture I'm about 40 degrees before the top dead centre and the default injector timing this is what the 360 refers to that is 360 degrees of crank rotation since top dead centre what we're going to be doing is testing where in this engine cycle is best to optimize the injection so here is a plot basically what I did was I fixed the ignition

Timing I also fixed ve table so that was running a cast ve all through the test it swept the injector timing from about 150 up through about 450 degrees I watched the RPM bear in mind that I'm zoomed way in that's going from a thousand at the bottom to 1250 at the top I did not adjust the throttle position sensor through the test the manifold air pressure presumably you'd want to minimize the manifold air pressures you can see the manifold air

Pressure coming down as you can see the RPM going up throughout the test here is the eg Oh correction or the exhaust gas correction the correction that the motor is making to the fueling based on what it's seeing at the o2 sensor you can see that it's a minimum in this area and increasing fuel as it goes through the test the pulse width is starting out relatively low and working its way a little higher and the AFR is pretty constant all the way through the range

Keep in mind that this is from 12 to 15 AFR so let's a fairly tight 13 and 1/2 AFR so now what I did is went to the Skinner plots and I plotted along the bottom is injector timing from about 100 140 up through about 450 on the vertical scale I'm running the e GL correction from a by 8% fuel pool there at 92 up through 105 and you can clearly see that the range the motor was running as I was at say a hundred and seventy degrees was right through this range

Did I get to 300 it's adding fuel as I got up into the 425 430 degrees range it was really adding fuel so you would think the optimum place to set your timing would be right here meaning that is the most efficient the motor could use the fuel in the eg Oh correction was pulling about five or six per cent on average in that area but then when I plotted the primary injector timing along the bottom just like before but I have manifold air pressure you'll

Notice the manifold air pressure went to a minimum at about three hundred and thirty degrees timing that's quite a bit different than the number we had before for the eg Oh correction you will also notice that the manifold air pressure is very the least in this area based on the height of where the sampling ended up each of these samples was about 10 15 seconds of idling but you can clearly see that there is a pattern now when I plot rpm for each of

These settings remember that I never touched the throttle position sensor during this entire test and you can see that the RPMs started coming down and then rising so you have to presume the best idle what the motor was happiest with 310 330 and 350 so 350-degree timing I then opened the same data in histogram view and basically what you're seeing is the injector timing here's where the injector timing was set at 150 170 190

And so on and so forth and manifold air pressure is what's in colour and you can clearly see at about 350 or 373 getting the maximum rpm so now if we go back to our four engine cycles core the way it's drawn is five because there are two intakes the range that I actually tested from was about here up through about 450 degrees notice that the leaf fuel was right about here and the lowest map manifold air pressure was there and the highest idle was just below the default

Setting of 360 so depending on what you want to maximize I would guess this motor would like to see somewhere in this range of about 340 degrees just as a way to optimize as many things as possible this is by no means the end-all everyone should use my settings this is really just a way to test I would like to thank my friends at tuner studio.com the developers of mega log viewer age see the software I use through this entire process to analyze the data and

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