Notes on optimising Fuel Injection Maps “on the road”

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Charlie54043
Posts: 14
Joined: Tue Jun 24, 2014 5:57 am
Location: Lincolnshire Coast

Notes on optimising Fuel Injection Maps “on the road”

Post by Charlie54043 »

This post follows 3 previous,

Inlet manifold length vs Torque and power,
Fuel Injection Build,
Determining actual WOT of TB's and its application,

These notes are for optimising the fuel map of Programmable Fuel Injection “on the road”. Although a Megasquirt ECU is used, they are applicable to most ECU's as they mainly concern the Maps and optimising process.

The amount of fuel injected is controlled by the Fuel Map and put simply, the ECU measures the angle of the throttle and the revs, then looks in the fuel map to see how much fuel is required and injects it. The result of the combustion can be measured with a wideband Lambda sensor and we use this to adjust the values in the Fuel Map to give the correct amount of fuel.

These adjustments (mapping) are often done on a rolling road, but this is expensive, so an alternative is to do the mapping while driving. ECU's have a very useful tool...logging software, which records what the injection system is doing and and the resulting AFR, then played back later.

The process of “on the Road” mapping is as follows:

Go for a drive with the logging software recording,
Review the log and adjust the values in the fuel map to give the correct AFR.
Go for another drive with the logging software recording.
Review the log and adjust the values in the fuel map to give the correct AFR.
Etc

Before going for a drive with the logging switched on, we need to think about what AFR's we want to see. For production engines, the AFR is kept as close as possible to 14.7:1 or Lambda 1 for the benefit of the Cat and emissions, but as we don't have Cat's we can take advantage of choosing what AFR our engines need to run smoothly, cleanly and safely, for example, at constant speed/load an AFR of 14.7 works well but at WOT/Hi Revs 12.7:1 is much safer.

It makes the optimisation process easier if we think of the Fuel map as a collection of areas and consider what AFR is needed for each particular area.

The first ”area” to consider is constant speed and shown are the “Fuel Bins” for 30, 40, 50, 60 and 70 mph.
constant Load-speed.jpg
constant Load-speed.jpg (336.95 KiB) Viewed 448 times

The Fuel Map above shows the throttle opening as the vertical scale, calibrated in ADC values from the Throttle Position Sensor (170 = wide open throttle, 32 = idle position throttle), the horizontal axis is engine revs and the amount of fuel injected at any particular TPS/Revs is the number in the rectangular “Bins”.
Highlighted in black are the constant speed bins. Adjust this area for AFR = 14.7:1

Area 2
Idle2.jpg
Idle2.jpg (337.02 KiB) Viewed 448 times


Area 2. Highlighted in Red are the bins used when the engine is idling. Adjust for AFR = 12.7

Area 3
Starting.jpg
Starting.jpg (318.53 KiB) Viewed 448 times

Area 3. Highlighted in Red are the bins used when starting or the throttle is blipped when idling or when pulling away from idle, this is a transient area so adjust for smoothest pick up. As can be seen, quite a lot of fuel needs to be added to stop the engine faultering or backfiring through the Throttle bodies.
Note: The 130/800 & 170/800 bins are set to zero fuel to provide Flood Clearing on starting. By holding full throttle at cranking, no fuel is injected, the Flood cleared and the engine should start.
Adjust fuel for a smooth “pick up”

Area 4
Actual WOT.jpg
Actual WOT.jpg (281.22 KiB) Viewed 448 times


Area 4. As mentioned in the “ Determining actual WOT of TB's and its application” post, the actual Wide Open Throttle point is less than the Real WOT, the engine cannot pump any more air by opening the throttle further in this area, so the highlighted in red bins are set to the same as the actual WOT. Adjust for AFR = 13.5:1

Area 5
Accel.jpg
Accel.jpg (335.04 KiB) Viewed 448 times



Area 5. Highlighted in red are the bins used when the car is accelerating or going up a hill and with the extra load, the mixture needs to be richened up. Adjust for AFR = 13.5

Area 6
Decel.jpg
Decel.jpg (335.49 KiB) Viewed 448 times

Area 6. Highlighted in red are the bins used when the car is decelerating or going down a hill, so with the reduced load the AFR can be weakened off. Adjust for AFR = 15:1

Area 7
WOT.jpg
WOT.jpg (333.15 KiB) Viewed 448 times

Area 7. Highlighted in red are the bins used for Wide Open Throttle and High Revs!!! Be careful here, damage can occur if the mixture goes weak, if in doubt...ADD FUEL! Adjust for AFR = 12.7:1!!!

Area 8
Not used often.jpg
Not used often.jpg (332.23 KiB) Viewed 448 times



Area 8, Highlighted in red are the bins used for part throttle at high revs, set slightly rich to avoid damage. Adjust for AFR 13.5:1

Area 9
Overrun.jpg
Overrun.jpg (330.22 KiB) Viewed 448 times

Area 9. Highlighted in red are the bins used on the overrun, set the fuel to give a slightly rich AFR to stop popping through the throttle bodies when “feathering” the throttle. Adjust for AFR = 13:1

On the Road:

So, you have the engine running and drivable (to a fashion!) now it's time to optimise the Fuel Map

Set up the logging software to record a minimum of 3 conditions, Throttle position, Revs and AFR.

Drive “round the block” and review the log.

Part of the log will look like something below,
Simple log2.jpg
Simple log2.jpg (352.78 KiB) Viewed 448 times
Green line = Revs, White line =TPS, Red line = AFR.

In the above pic of a recorded Log, the engine is accelerating hard and reading the measurements off the central cursor, Revs = 2993, throttle position = 39, AFR = 16.9:1....16.9:1 is very weak for Area 7.....it should be around 12.7:1. So go to the Fuel Map and increase the fuel in the 105/2800 bin by quite a bit.

Note...The log TPS value ( 39 ) on the cursor is not the same as the MegaSquirt TPS value in the Fuel Map! so a “fiddle factor” has to be applied and Log TPS 39 = M.S. Fuel Map 105, hence adjusting the 105/2800 Fuel Map bin.

Go through the whole Log increasing the fuel in the bins where the mixture is weak and decreasing the fuel in the bins where the mixture is rich with reference to the suggested AFR.

As your fuelling get close to correct, you can turn on the Closed Loop Control which will automatically adjust the fuel to the correct AFR.

But firstly, your chosen AFR's need to be entered into your “AFR Target Map” which tells the Closed Loop Control what AFR value is required, also add Closed Loop Control to the Logging conditions.

Time to go out for yet another drive with the logging software running/Closed Loop control switched on and the ECU will adjust the fuel to achieve the target AFR and record the conditions.

Review the log, which will now show what the Closed Loop Control was doing and can be used to speed up adjustments by noting the Closed Loop value and adjusting the Fuel Map Bin by the same %. Below is an example:
log with Closed loop.jpg
log with Closed loop.jpg (376.5 KiB) Viewed 448 times

Green line = Revs, Red line = AFR, White Line = TPS, Yellow Line = Closed loop control

Looking at the values on the Cursor, TPS = 5, Revs = 1685, AFR = 14.33:1 and the Closed Loop Control = 103%.

This indicates that the car is driving steadily at around 30 mph with almost the correct mixture ( closed loop is only adding 3% extra fuel...not bad! ) and therefore no fuel adjustments needed. But....look to the left of the cursor, it can now be seen that the Closed Loop is at 110%, go back to the fuel map TPS/Revs bin and add 10% ( the mixture would have been too weak without this automatic addition )

Do this for the whole log, noting whether Closed Loop Control is adding or subtracting fuel and make the same adjustments to the Fuel Map Bins.

Then go out for another drive with the log recording, review that log and adjust the Fuel Bins, etc.

It will take many runs ( a good excuse to go out for a “Hoon”! ) but soon you'll have a fuel map that will be fairly close to the AFR's you want, I haven't adjusted any bins for probably the last 6 months.

Below is my current Fuel map, the Closed Loop control stays within Plus or Minus 10% under all conditions.
fuel map.jpg
fuel map.jpg (270.08 KiB) Viewed 448 times


The next post will be how to make and use a Knock Sensor necessary for optimising the Ignition Map “on the road”

Happy Davrianing, Charlie
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