How the ECU works

I've used the course section how the ECU works to attempt to create my own base fuel map.

The issue I have is that the injector pulse width calculation I'm coming up with seems incredibly high.

Could someone please run these specs and let me know where I've gone wrong?

4.8 Litre Nissan DOHC Straight 6

Engine CC = 4800 which = 293 CI

380cc Injectors

6 Cylinder Engine

Calculated at 6000 RPM

509 cf/min mass air flow which = 509 X 0.076 (Standard Conditions) = 38.68 lb/min air flow through engine per minute

Mass flow per cylinder = 6.45 lb/min as it is 6 cylinder

Desired AFR @ 6000RPM = 12.5

Therefore Mass fuel flow = 0.516 lb/min required

Injectors 380CC = 36.2 lb/hour

Calculate inj flow per min

36.2/60 = 0.60 lb/min

20 ms Cycle time @ 6000 RPM

Inj Duty cycle = required mass fuel flow / total mass fuel flow

Therefore 0.516/0.60 = 86% Duty Cycle

Inj Pulse width = Cycle time X Duty Cycle = 17.2 ms

This seems really high.

This is using the 380CC Standard injector as fitted to this engine.

When looking at all other Nissan traditional fuel models the master Inj Duration is around 12 ms with the Fuel map entries around 50-60% at the 6000 RPM mark

Any assistance would be great.

Cheers.

Your math all looks pretty much on point, however I think the part you've overlooked though is the calculation you just went through assumes 100% VE. If you instead assume the VE is perhaps 85% at 6000 rpm then the mass airflow becomes 6.45 x .85 = 5.48 lb/min. If you now calculate the required mass of fuel, this becomes 0.438 lb/min. Lastly if we calculate required injector duty cycle, this becomes 73% which gives a required pulse width of 14.6 ms.

I've had nothing to do with the TB48 so I can't comment on typical values sorry, however you can see from the above though that the engines VE makes a massive difference to the required fuel mass. In practice unless you accurately know the engine's VE, calculating required injector pulse width is seldom used to tune the fuel table. The example is simply in the course so you understand the steps that are required.

*EDIT* Just had a quick google of TB48 specs and wiki lists them at 248 hp @ 4800 rpm and 310 ft/lb @ 3600. Given these operating points, it's likely that the VE would have dropped quite dramatically by 6000 rpm.

Thanks Andre,

My goal is to be able to fairly accurately set a base fuel map in traditional mode for a Link/Vipec ECU. I have a VE based table from the Haltech PnP software and also the attached Excel to quickly calculate injection duration. What is the best way to go about setting up a table from the start?

As I understand it the traditional model sets the injection % based on 100 Kpa MAP, so for example if at say 100 Kpa MAP @ 6000 RPM the duration was 50% of a master duration of 20ms this would be 10ms duration. Then at 50K KPA @ 6000RPM the duration was also 50% this would actually be half of the master 20ms and 50% of that being 5ms. Is that correct?